Biochimie

The insulin superfamily proteins (ISPs), in particular, insulin, IGFs and relaxins are key modulators of animal physiology. They are known to have evolved from the same ancestral gene and have diverged into proteins with varied sequences and distinct functions, but maintain a similar structural architecture stabilized by highly conserved disulphide bridges. A recent surge of sequence data and the structures of these proteins prompted a need for a comprehensive analysis which connects the evolution of these sequences in the light of available functional and structural information and their interaction with cognate receptors. This study reveals a) unusually high sequence conservation of IGFs (>90%), which has never been reported before. In fact, it was interesting to observe that the functional domains (excluding signal peptide) of human, horse, pig and Ords kangaroo rat are 100% identical. (b) an updated definition of the signature motif of the relaxin family (c) a non-canonical C-peptide cleavage site in a few killifish insulin sequences and so on. We also provide a structure-based rationale for such conservation by introducing a concept called binding partners imposed evolutionary constraints. Furthermore, the high conservation of IGFs appears to represent a classic case of resistance to sequence diversity exerted by physiologically important interactions with multiple partners. Furthermore, we propose a probable mechanism for C-peptide cleavage in killifish insulin sequences.

A neuropeptide (Sco-CHH-L), belonging to the crustacean hyperglycemic hormone (CHH) superfamily and preferentially expressed in the pericardial organs (POs) of the mud crab Scylla olivacea, was functionally and structurally studied. Its expression levels were significantly higher than the alternative splice form (Sco-CHH) in the POs and increased significantly after animals were subjected to a hypo-osmotic stress. Sco-CHH-L, but not Sco-CHH, significantly stimulated in vitro the Na+, K+-ATPase activity in the posterior (6th) gills. Furthermore, solution structure of Sco-CHH-L was resolved using nuclear magnetic resonance spectroscopy revealing that it has an N-terminal tail, three -helices (2, Gly9-Asn28; 3, His34-Gly38; 5, Glu62-Arg72), and a {pi}-helix ({pi}4, Cys43-Tyr53) and is structurally constrained by a pattern of disulfide bonds (Cys7-Cys43, Cys23-Cys39, Cys26-Cys52), which is characteristic of the CHH superfamily-peptides. Sco-CHH-L is topologically most similar to the molt-inhibiting hormone from the Kuruma prawn Marsupenaeus japonicus with a backbone root-mean-square-deviation of 3.12 [A]. Ten residues of Sco-CHH-L were chosen for alanine-substituted and the resulting mutants were functionally tested using the gill Na+, K+-ATPase activity assay, showing that the functionally important residues (I2, F3, E45, D69, I71, G73) are located at either end of the sequence, which are sterically close to each other and presumably constitutes the receptor binding sites. Sco-CHH-L was compared with other members of the superfamily revealing a molecular architecture, which is suggested to be common for the crustacean members of the superfamily, with the properties of the residues constituting the presumed receptor binding sites being the major factors dictating the ligand-receptor binding specificity.

There was a huge variability in the pharmacokinetics of drugs between species, which means in the way it will be transformed, degraded and eliminated, as well as the variation in drug absorption, plasma concentration over time, half-life, bioavailability, volume of distribution, metabolism rate, and routes of excretion. To understand the reasons of such a variability between species, we have studied here the evolution of genes encoding drug-metabolizing enzymes, i.e. the 9 key genes that are known to play a principal role in this process: UGT1A6, UGT1A, CYP2B, CYP2C, CYP2D, UGT2B, CYP3A, NAT1, GSTP1. We show here that a lot of these genes have been lost during evolution in several vertebrate species: UGT1A6 in gorilla, cat dog, ruminants, pig, UGT1A in artiodactyla, UGT2B in all vertebrate species except human and gorilla, CYP2C in all vertebrate species except primates and mouse. Several of these genes have duplicated such as UGT1A in human (4 copies), CYP3A in most of vertebrate species studied here except the cat, CYP2D in the mouse (9 copies). Furthermore, several of these genes undergone evolution by positive selection such as CYP2D6, UGT1A, CYP2C (particularly in squirrel), UGT1A. Overall, this study shows that the evolution by gene death, gene duplication, and positive selection is partly responsible for the great variability in the ability of vertebrate species to metabolize drugs.

The CaV1 and CaV2 families of voltage-dependent calcium channels play a crucial role in neurotransmitter release, excitation-contraction and many other cellular processes. Comprised of the membrane pore-forming 1, intracellular {beta} and extracellular 2{delta} subunits, these channels have been targets for pharmacological intervention for decades. Physiological functions of CaV channels are attenuated by either constitutively or transiently bounds proteins in the cellular environment. The RGK (Rad, Gem, Rem, and Rem2) G-protein family potently inhibits CaV1 and CaV2 function in heterologous expression systems. RGK proteins bind to CaV{beta} and inhibit channel localization and activity by forming a ternary complex with CaV1. Here, we evaluated the influence of RGK proteins on CaV2.2 channels heterologously expressed in Xenopus oocytes. Both Gem and Rad showed no nucleotide dependency on its inhibitory function on CaV2.2. The G-domain and C-terminus could inhibit the CaV2.2 channel independently when co-expressed with channel subunits. Our results demonstrated that structural determinants in Gem, crucial for channel inhibition, lie within the 222-296 amino acid region containing both the partial G-domain and C-terminus as determined from chimeric CaV{beta}-Gem constructs. We expanded our mapping efforts and prepared various chimeras of Drosophila melanogaster (Dm) RGK sequences fused to CaV{beta} and showed that 22 residues in RGK2t and RGK3L C-terminal imparted complete CaV2.2 inhibition. Point mutations in the DmRGK C-terminus, conserved in mammalian RGK proteins, abrogated the CaV2.2 inhibition to a significant extent, pointing to a hot region in the extreme C-terminus for inhibition of CaV channels. Since RGK homologs are now recognized as physiological modulators in {beta}-adrenergic regulation of CaV channels, the relevance of this curious G-protein family deserves close examination.

The gastric peptide ghrelin and its receptor GHSR have important functions in energy metabolism. Recently, liver-expressed antimicrobial peptide 2 (LEAP2) was identified as an endogenous antagonist for GHSR. Ghrelin, LEAP2, and GHSR are ubiquitously present from fishes to mammals and are highly conserved in evolution. However, our recent study suggested that GHSRs from the Actinopterygii fish Danio rerio (zebrafish) and Larimichthys crocea (large yellow croaker) have lost their binding to ghrelin, despite binding normally to LEAP2. Do these fish GHSRs use another peptide as their agonist? To answer this question, in the present study, we tested to two fish motilins that are closely related to ghrelin. In ligand binding and activation assays, the fish GHSRs from D. rerio and L. crocea displayed no detectable or very low binding to all tested motilins; however, the GHSR from the Sarcopterygii fish Latimeria chalumnae (coelacanth) bound to its motilin with high affinity and was efficiently activated by it. Therefore, it seemed that motilin is not a ligand for GHSR in D. rerio and L. crocea, but is an efficient agonist for GHSR in L. chalumnae, which is known as a living fossil and is believed to be one of the closest fish ancestors of tetrapods. The results of present study suggested that in ancient fishes, GHSR had two efficient agonists, ghrelin and motilin; however, this feature might be only preserved in some extant fishes with ancient evolutionary origins. Our present work shed new light on the ligand usage of GHSR in different fish species and in evolution.

The renin-angiotensin system (RAS) comprises a biochemical cascade that hydrolyzes angiotensinogen into several different bioactive peptides, which can activate different receptors promoting plenty of specific effects. The aim of this study was to evaluate the presence of the putative product of alamandine, the pentapeptide alamandine-(1-5) in the circulation and its biological activity. To accomplish this we have used mass spectrometry (MALDI/TOF/TOF, LC-MS/MS) and several methodologies including isolated blood vessels, isolated perfused hearts, isolated cardiomyocytes, blood pressure recording in freely-moving normotensive and hypertensive rats (SHR), high resolution echocardiography (VEVO 2100), central administration (ICV infusion and microinjection in the insular cortex), cell culture (endothelial cells and GPCR-transfected CHO cells) and wild type and Mas, MrgD or AT2R deficient mice. Our results show that alamandine-(1-5) circulates in the human and rodent blood and promotes many biological central and peripheral actions. More importantly, its plasma concentration is increased in pediatric nephropathic patients. A major role for plasma ACE activity in the formation of alamandine-(1-5) from alamandine was observed using plasma samples from Angiotensinogen-KO mice. Alamandine-(1-5) increased Baroreflex sensitivity and produced a long-lasting ([~]6 hours) anti-hypertensive effect in SHR, associated with a significant reduction in cardiac output. A particularly important effect of this pentapeptide was observed in isolated perfused heart and cardiomyocyte contractility (reduced inotropism). It was capable of stimulating NO production through all receptors from the renin-angiotensin protective arm, (MAS, MrgD and AT2R) in CHO-transfected cells. Our data shows that Alamandine-(1-5) exhibits selective actions that set it apart from traditional concepts of the vasodilatory axis of the RAS and that are possibly intricately linked to a complex interplay between Mas, MrgD and AT2 receptors. This novel finding suggests that RAS may possess a complexity that surpasses our current understanding.

Fibroblast growth factor 19 (FGF19) is a hormone with pleiotropic metabolic functions, leading to ongoing development of analogues for the treatment of metabolic disorders. On the other hand, FGF19 is overexpressed in a sub-group of hepatocellular carcinoma (HCC) patients and has oncogenic properties. It is therefore crucial to precisely define FGF19 effects, notably chronic exposure to elevated concentrations of the hormone. We used hydrodynamic gene transfer approach to generate a transgenic mouse model with long-term FGF19 hepatic overexpression. Here we describe a novel effect of FGF19, namely stimulation of water intake. This phenotype, lasting at least over a 6-month period, depends on signaling in the central nervous system and is independent of FGF21, although it mimics some of its features. We further show that HCC patients with high levels of circulating FGF19 have a reduced natremia, indicating dispogenic features. The present study provides evidence of a new activity for FGF19, which could be clinically relevant in the context of FGF19 overexpressing cancers and treatment of metabolic disorders by FGF19 analogues.

Nuclear receptors (NRs) are important transcriptional modulators in metazoans. Typical NRs possess a conserved DNA binding domain (DBD) and a ligand binding domain (LBD). Since we discovered a type of novel NRs each of them has two DBDs and single LBD (2DBD-NRs) more than decade ago, there has been very few studies about 2DBD-NRs. Recently, 2DBD-NRs have been only reported in Platyhelminths and Mollusca and are thought to be specific NRs to lophotrochozoan. In this study, we searched different databases and identified 2DBD-NRs in different animals from both protostomes and deuterostomes. Phylogenetic analysis shows that at least two ancient 2DBD-NR genes were present in the urbilaterian, a common ancestor of protostomes and deuterostomes. 2DBD-NRs underwent gene duplication and loss after the split of different animal phyla, most of them in a certain animal phylum as paralogues, rather than orthologues, of that in another animal phylum. Amino acid sequence analysis shows that the conserved motifs in typical NRs are also present in 2DBD-NRs and they are gene specific. From our phylogenetic analysis of 2DBD-NRs and following the rule of Nomenclature System for the Nuclear Receptors, a nomenclature for 2DBD-NRs is proposed.

26RFa (QRFP) is a biologically active peptide that regulates glucose homeostasis by acting as an incretin and by increasing insulin sensitivity at the periphery. 26RFa is also produced by a neuronal population localized in the hypothalamus. In the present study, we have investigated whether the 26RFa neurons may be involved in the hypothalamic regulation of glucose homeostasis. Our data indicate that 26RFa, i.c.v. injected, induces a robust antihyperglycemic effect associated with an increase of insulin production by the pancreatic islets. In addition, we found that insulin strongly stimulates 26RFa expression and secretion by the hypothalamus. RNAscope experiments revealed that neurons expressing 26RFa in the lateral hypothalamic area and the ventromedial hypothalamic nucleus also express the insulin receptor and that insulin induces the expression of 26RFa in these neurons. Concurrently, we show that the central antihyperglycemic effect of insulin is abolished in presence of a 26RFa receptor (GPR103) antagonist as well as in mice deficient for 26RFa. Finally, our data indicate that the hypothalamic 26RFa neurons are not involved in the central inhibitory effect of insulin on hepatic glucose production, but mediate the central effects of the hormone on its own peripheral production. To conclude, in the present study we have identified a novel actor of the hypothalamic regulation of glucose homeostasis, the 26RFa/GPR103 system and we provide the evidence that this neuronal peptidergic system is a key relay for the central regulation of glucose metabolism by insulin.

The nicotinic acetylcholine receptors (nAChR) belong to a large family of ligand-gated ion channels and are involved in the mediation of fast synaptic transmission. Each receptor is made up of five subunits that arrange symmetrically around a central pore. Despite the similarity in their sequences and structures, the properties of these subunits vary significantly. Thus, identifying the function-related sites specific to each subunit is essential for understanding the characteristics of the subunits and the receptors assembled by them. In this study, we examined the sequence features of the nine neuronal nAChRs subunits from twelve representative vertebrate species. Analysis revealed that all the subunits were subject to strong purifying selection in evolution, and each was under a unique pattern of selection pressures. At the same time, the functional constraints were not uniform within each subunit, with different domains in the molecule being subject to different selection pressures. Via evolutionary analyses, we also detected potential positive selection events in the subunits or subunit clusters, and identified the sites might be associated with the function specificity of each subunit. Furthermore, positive selection at some domains might contributed to the diversity of subunit function; for example, the {beta}9 strand might be related to the agonist specificity of subunit in heteromeric receptor and {beta}4-{beta}5 linker could be involved in Ca2+ permeability. Subunits 7, 4 and {beta}2 subunits possess a strong adaptability in vertebrates. Our results highlighted the importance of tracking functional differentiation in protein sequence underlying functional properties of nAChRs. In summary, our work may provide clues on understanding the diversity and the function specificity of the nAChR subunits, as well as the receptors co-assembled by them.

Obesity is a medical condition associated with serious medical and psycho-social consequences and an augmented body fat mass. Several compounds were suggested to counteract obesity and fat accumulation with variable degrees of success. Searching for a safe and effective anti-adipogenic substance, we found that cuminaldehyde-rich essential oil extracted from Calligonum comosum potentially mediate activities. The results showed that C. comosum essential oil and its major component cuminaldehyde, selectively caused significant reduction in the viability of 3T3-L1 cells when compared to fibroblasts. Furthermore, cuminaldehyde caused significant reduction in the lipid content, glucose uptake and levels of both triglycerides and cholesterol in adipocytes. Moreover, the formation of 3D-adipocyte pellets in the presence of cuminaldeyde was affected. Adipocytes matured in the presence of cuminaldehyde have significant reduction in the expression of adipocyte-specific transcripts, CAAT-enhancer binding protein alpha (CEBPa) and Peroxisome proliferator-activated receptor gamma (PPARg). Taken together, these results demonstrate a potential inhibitory role of cuminaldehyde extracted from C. comosum oil on lipid accumulation. Consequently, cuminaldeyde can be considered as a new potential anti-adipogenic agent for prevention and treatment of obesity.

1Members of the parvalbumin (PV) family of calcium binding proteins are found in a variety of vertebrates, where can they influence neural functions, muscle contraction and immune responses. It was reported that the -parvalbumin (PV)s AB domain comprising two -helices, dramatically increases the proteins calcium (Ca2+) affinity by {approx}10 kcal/mol. To understand the structural basis of this effect, we conducted all-atom molecular dynamics (MD) simulations of WT PV and truncated -parvalbumin ({Delta}PV) constructs. Additionally, we also examined the binding of magnesium (Mg2+) to these isoforms, which is much weaker than Ca2+ (Mg2+ actually does not bind to the {Delta}PV). Our key finding is that reorganization energies (RE) assessed using molecular mechanics generalized Born approximation (MM/GBSA) correctly rank-order the variants according to their published Ca2+ and Mg2+ affinities. The [Formula] of the {Delta}PV compared to the wild-type (WT) is 415.57{+/-}0.55 kcal/mol, indicating that forming a holo state of {Delta}PV in the presence of Ca2+ incurs a greater reorganization penalty than the WT. This is consistent with the {Delta}PV exhibiting lesser Ca2+ affinity than the WT ({approx}9.5 kcal/mol). Similar trend was observed for Mg2+ bound variants as well. Further, we screened for metrics such as oxygen coordination of EF hand residues with ions and found that the total oxygen coordination number (16 vs. 12 in WT:Ca2+ and {Delta}PV:Ca2+) correlate with the reported ion affinities (-22 vs. -12.6 kcal/mol in WT:Ca2+ and {Delta}PV:Ca2+), which indicates that AB domain is required for the protein to coordinate with maximal efficiency with the binding ions. To our surprise, no significant differences were observed between the Mg2+ bound WT and {Delta}PV isoforms. Additionally, we have screened for factors such as total number of waters, hydrogen bonds, protein helicity and {beta}-content for the entire protein, which enables us to understand the impact of lack of AB domain on the entire structure and not just binding sites. Our data indicate that AB improves the overall helicity ({approx}5%) in apo as well as holo forms. Particularly, AB increases -helicity in the D-helix residues (i.e., 60-65) upon ion binding by {approx}35% (90% vs. 55% in the Ca2+ bound WT and {Delta}PV, 60% vs. 20% in the Mg2+ bound WT and {Delta}PV), which likely contributes to high Ca2+ binding affinity. On the contrary, no significant effect on the overall {beta}-content was observed. Similarly, increased dehydration ({approx}50) and increase in total number of hydrogen bonds ({approx}7) were observed upon ion binding in both the WT and {Delta}PV systems, however, no significant differences were observed between the WT and {Delta}PV variants and also between Ca2+ and Mg2+ isoforms. We speculate that this is due to the partially folded apo state that was captured in our MD simulations, which might not be physiologically relevant as suggested by NMR experiments [1]. Also, we have identified seven different interactions that might play a key role in binding the AB domain with the CDEF helices, particularly the D22(AB)-S78(CDEF) hydrogen bond. Overall, this study indicates that local (i.e., the EF hands) as well as global factors play a role in improved ion binding due to AB domain.

India confines more than 17% of the worlds population and has a diverse genetic makeup with several clinically relevant rare mutations belonging to many sub-group which are undervalued in global sequencing datasets like the 1000 Genome data (1KG) containing limited samples for Indian ethnicity. Such databases are critical for the pharmaceutical and drug development industry where the diversity plays a crucial role in identifying genetic disposition towards adverse drug reactions. A qualitative and comparative sequence and structural study utilizing variant information present in the recently published, largest curated Indian genome database (IndiGen) and the 1000 Genome data was performed for variants belonging to the kinase coding genes,the second most targeted group of drug targets. The sequence level analysis identified similarities and differences among different populations based on the nsSNVs and amino acid exchange frequencies whereas comparative structural analysis of IndiGen variants was performed with pathogenic variants reported in UniProtKB Humsavar data. The influence of these variations on structural features of the protein, such as structural stability, solvent accessibility, hydrophobicity, and the hydrogen-bond network were investigated. In-silico screening of the known drugs to these Indian variation-containing proteins reveal critical differences imparted in the strength of binding due to the variations present in the Indian population. In conclusion, this study constitutes a comprehensive investigation into the understanding of common variations present in the second largest population in the world, and investigating its implications in the sequence, structural and pharmacogenomic landscape. The preliminary investigation reported in this paper, supporting the screening and detection of ADRs specific to the Indian population could aid in the development of techniques for pre-clinical and post-market screening of drug-related adverse events in the Indian population.

Bioactive fractions or compounds obtained from medicinal plants have been used for the treatment of multiple diseases. This effect could be due to common pathways underlying these conditions that are targeted by such medicines. In this study, we explored the molecular basis of action of one such herbal formulation Cissampelos pareira, used for the treatment of female hormone disorders and fever. Genome-wide expression studies on MCF7 cell lines treated with Cipa extract were carried out using Affymetrix arrays. Transcriptome analysis revealed a downregulation of signatures of estrogen response governed by estrogen receptor (ER). Molecular docking analysis identified 38 constituent molecules in Cipa that potentially bind ({Delta}G< -7.5) with ER at the same site as estrogen. Cipa transcriptome signatures show high positive connectivity (https://clue.io/) scores with protein translation inhibitors such as emetine (score: 99.61) and knockdown signatures of genes linked to the antiviral response such as ribosomal protein RPL7 (score: 99.92), which is also an ER coactivator. Cipa exhibits antiviral activity in dengue infected MCF7 cells that is decreased upon ESR1 (estrogen receptor 1) gene knockdown. This approach reveals a novel pathway involving ESR1-RPL7 axis that could be a potential target in dengue viral infection.

Cocaine- and amphetamine-regulated transcript (Cart) is a pleiotropic neuropeptide involved in the regulation of stress and anxiety, depression, reproduction and circadian functions, yet it is mainly known for its metabolic regulation of body weight and appetite. While mammals possess a single cart gene, the genomes of birds may contain up to two carts and fish may possess up to ten cart genes. Furthermore, in some fish species the number of cart paralogues exceeds the number expected according to whole-genome duplication events in actinopterygians, suggesting a species-specific diversification of the cart system. In the current study, we identified multiple cart genes in two fish species with global importance -Nile tilapia and gilthead seabream. Bioinformatics analysis revealed seven cart genes in the tilapia genome and six cart genes in the seabream genome, all of which show high homology with carts of other vertebrates. Additionally, the predicted mature cart peptide sequences contain all the cysteines known to stabilize the tertiary peptide structure in other vertebrates. Nevertheless, protein structure modeling suggested that some carts lost part or all of the cysteine-based disulfide bridges. Quantitative-PCR analyses of all cart genes cloned in this research demonstrated that while all carts are mainly expressed in the brain, some cart genes show wider tissue distribution with significant expression in peripheral tissues including the kidney and gonads. Taken together, these findings emphasize the complexity of the piscine cart system.

N-Carbamoyl-{beta}-Alanine Amidohydrolase (C{beta}AA) constitute one of the most important groups of industrially relevant enzymes used in production of optically pure amino acids and derivatives. In this study, a N-carbamoyl-{beta}-alanine amidohydrolase encoding gene from Rhizobium radiobacter MDC 8606 was cloned and overexpressed in Escherichia coli. The purified recombinant enzyme (RrC{beta}AA) showed a specific activity of 14 U/mg using N-carbamoyl-{beta}-alanine as a substrate with an optimum activity of 55{degrees}C at pH 8.0. In this work, we report also the first prokaryotic N-carbamoyl-{beta}-alanine amidohydrolases structure at a resolution of 2.0 [A]. A discontinuous catalytic domain and a dimerization domain attached through a flexible hinge region at the domain interface has been revealed. We have found that the ligand is interacting with a conserved glutamic acid (Glu131), histidine (H385) and arginine (Arg291) residues. Studies let us to explain the preference on the enzyme for linear carbamoyl substrates as large carbamoyl substrates cannot fit in the active site of the enzyme. This work envisages the use of RrC{beta}AA from the Rhizobium radiobacter MDC 8606 for the industrial production of L--, L-{beta}-, and L-{gamma} - amino acids. The structural analysis provides new insights on enzyme-substrate interaction, which shed light on engineering of N-carbamoyl-{beta}-alanine amidohydrolases for high catalytic activity and broad substrate specificity.

Adipokines are key factors in regulating energy homeostasis. We identified a novel adipokine; we named it Leptolin. In humans, leptolin levels in white adipose tissue were positively corrected with exercise, and negatively associated with body mass index. Leptolin levels were positively correlated with lipolysis-promoting gene expression. Elevated leptolin in plasma of athletes, whereas lowered leptolin in plasma of obese individuals were observed. Leptolin gene-knockout mice exhibited increased adiposity and body weight, and decreased energy expenditure. Leptolin gene-overexpression mice showed obesity-resistant phenotypes. Treatment with leptolin promoted fat mobilization and energy expenditure, and reduced body weight, without affecting food-intake and motor activity. Together, leptolin, a novel adipokine with a capacity to improve metabolic status, may serve as a new therapeutic agent for obesity and metabolic disorders.

G protein-coupled receptor 83 (GPR83) is primarily expressed in the brain and is implicated in the regulation of energy metabolism and some behaviors. Recently, the PCSK1N/proSAAS-derived peptide PEN, the procholecystokinin-derived peptide proCCK56-63, and family with sequence similarity 237 member A (FAM237A) were all reported as agonists of GPR83. However, these results have not yet been reproduced by other laboratories and thus GPR83 is still officially an orphan receptor. The PEN and proCCK56-63 share sequence similarity; however, they are completely different from FAM237A, raising doubts that all of them are ligands of GPR83. To identify its actual ligand(s), in the present study we developed a NanoLuc Binary Technology (NanoBiT)-based ligand-binding assay, fluorescent ligand-based visualization, and a NanoBiT-based {beta}-arrestin recruitment assay for human GPR83. Using these assays, we demonstrated that mature human FAM237A could bind to GPR83 with nanomolar range affinity, which activated this receptor and induced its internalization in transfected human embryonic kidney 293T cells. However, we did not detect any interaction of PEN and proCCK56-63 with GPR83 using these assays. Thus, the results confirmed that FAM237A is an agonist of GPR83, but did not support PEN and proCCK56-63 as ligands of this receptor. Clarification of its actual endogenous agonist will pave the way for further functional studies of this brain-specific receptor. The present study also provided an efficient approach for the preparation of mature FAM237A, which would facilitate further functional studies of this difficult-to-make peptide in the future.

Here we report proteolysis of synthetic acylated human ghrelin by recombinant human insulin-degrading enzyme (IDE). Kinetic parameters and sites of proteolytic cleavage were evaluated. Ghrelin proteolysis by IDE was inhibited by ethylenediaminetetraacetate (EDTA), a metal chelating agent. Ghrelin proteolysis appears at least somewhat specific to M16 family proteases such as IDE, as the M13 protease neprilysin (NEP) did not exhibit ghrelin proteolysis in this study. A quenched fluorogenic peptide substrate comprising the primary sites of IDE-mediated ghrelin proteolysis (Mca-QRVQQRKESKK(Dnp)-OH; Mca: 7-methoxycoumarin-3-carboxylic acid; Dnp: 2,4-dinitrophenyl) was developed and used to evaluate enzyme specificity and kinetic parameters of proteolysis. Like acyl ghrelin, Mca-QRVQQRKESKK(Dnp)-OH was efficiently cleaved by IDE central to the target sequence. We anticipate that this quenched fluorogenic peptide substrate will be of value to future studies of ghrelin proteolysis by IDE and potentially other peptidases.

The calcium-sensing receptor (CaSR) is responsible for sustaining a stable blood calcium concentration. Consequently, genetic and acquired changes in this G protein-coupled receptor can give rise to various calcium homeostasis disorders. Synthetic positive allosteric modulators targeting CaSR are currently used to treat hypercalcemia, but their usage is highly limited due to the high risk of severe hypocalcemia and gastrointestinal intolerance. In this study, we aimed to generate pharmacologically active CaSR-specific nanobodies that could be employed as a new generation of pharmacological tools to investigate the receptor function and potentially serve as a new drug modality for effective treatment of CaSR-related disorders. Nanobodies were generated by immunization of a llama with CHO cells recombinantly overexpressing a myc-epitope-tagged human CaSR. Following construction of a phage display library representing the repertoire of nanobody genes, nanobodies binding to the CaSR were isolated by FACS of whole HEK293 cells recombinantly overexpressing HA-epitope-tagged human CaSR. Based on sequence comparison, 37 nanobodies from 25 different sequence families were purified and subsequent characterized in vitro for modulation of CaSR signaling. The nanobodies were screened for agonist, as well as positive and negative allosteric modulators activity in in vitro cellular assays downstream of CaSR activation. We identified eight pharmacologically active nanobodies acting as positive allosteric modulators that could be divided into five main families based on their sequence identity. The most potent nanobody (Nb4) binding to the extracellular domain of CaSR was slightly more potent than the reference small molecule PAM NPS R-568. This study describes the discovery and pharmacological characterization of nanobodies acting as potent CaSR positive allosteric modulators. These nanobodies are a new class of pharmacological research tools for the CaSR, which potentially can be developed into new therapeutics in the treatment of CaSR-related disorders.