Solution-state NMR Assignment and Secondary Structural Propensities of the Full-Length and Minimalistic-Truncated Prefibrillar Monomeric Form of Biofilm-Forming Functional-Amyloid FapC from Pseudomonas aeruginosa

Functional bacterial amyloids provide structural scaffolding to bacterial biofilms. In contrast to the pathological amyloids, they have a role in vivo and are tightly regulated. Their presence is essential to the integrity of the bacterial communities surviving in biofilms and may cause serious health complications. Targeting amyloids in biofilms could be a novel approach to prevent chronic infections. However, structural information is very scarce on them in both soluble monomeric and insoluble fibrillar forms, hindering our molecular understanding and strategies to fight biofilm related diseases. Here, we present solution-state NMR assignment of 250 amino acid long biofilm-forming functional-amyloid FapC from Pseudomonas aeruginosa. We studied the full-length and shorter minimalistic-truncated FapC constructs without signal-sequence that is required for secretion. 91% and 100% backbone NH resonance assignment for FL and short constructs, respectively, indicates that soluble monomeric FapC is predominantly disordered, with sizeable secondary structural propensities mostly as PP2 helices, but also as -helices and {beta}-sheets highlighting hotspots for fibrillation initiation interface. Shorter construct showing almost identical NMR chemical shifts highlights the promise of utilizing it for more demanding solid-state NMR studies that requires methods to alleviate signal redundancy due to almost identical repeat units. This study provides key NMR resonance assignment for future structural studies of soluble, pre-fibrillar and fibrillar forms of FapC.