Biophysical characterization of the human K0513 protein

Glioblastoma multiforme (GBM) is an aggressive grade IV primary malignant tumour which accounts for 78 % of all brain tumours. K0513 is a GBM biomarker that is upregulated in the invasive phenotype. K0513 is expressed ubiquitously and is reportedly enriched in the cerebral cortex of the brain. K0513 is further implicated in signalling pathways involving neuroplasticity, cytoskeletal regulation and apoptosis. The protein encoded by K0513 is a prospective biomarker for pancreatic cancer prognosis. However, the gene product of K0153 is not well characterised. This study focused on structure-function characterisation of human K0513 protein. To this end, we employed bioinformatics analysis and biophysical approaches to characterize the protein. In silico structural characterisation of the human K0513 protein suggests the presence of a SET binding factor 2 (SBF2) domain and a transmembrane region. The SBF2 domain is found in the Myotubularin-related protein 13 (MTMR13), which may function as a nucleotide exchange factor for the RAS-associated GTPase, Rab28. K0513 was predicted to interact with RAS-associated GTPase, Rab3a. Secondary structure prediction revealed K0513 to be predominantly -helical in nature. The predicted three-dimensional model of K0513 showed a globular fold, suggesting that the protein is water-soluble. K0513 was heterologously expressed in E. coli XL1-Blue cells and subsequent purification yielded 80 % soluble protein. Biophysical characterisation using tryptophan-based fluorescence spectroscopy and limited proteolysis showed the conformation of K0513 is mostly unperturbed in the presence of nucleotides. Interestingly, K0513 was detected in lung carcinoma, fibrosarcoma and cervical adenocarcinoma cells, supporting its possible role in cancer signalling pathways.