Polycystin-1 is a large transmembrane protein, which, whenmutated, causes autosomal dominant polycystic kidney disease, one of\r\nthe most common life-threatening genetic diseases that is a leading cause of kidney failure.The REJ (receptor for egg lelly) module\r\nis a major component of PC1 ectodomain that extends to about 1000 amino acids. Many missense disease-causing mutations map\r\nto this module; however, very little is known about the structure or function of this region. We used a combination of homology\r\nmolecularmodeling, protein engineering, steered molecular dynamics (SMD) simulations, and single-molecule force spectroscopy\r\n(SMFS) to analyze the conformation and mechanical stability of the first ~420 amino acids of REJ. Homology molecular modeling\r\nanalysis revealed that this regionmay contain structural elements that have an FNIII-like structure, which we named REJd1, REJd2,\r\nREJd3, and REJd4.We found that REJd1 has a higher mechanical stability than REJd2 (~190 pN and 60 pN, resp.). Our data suggest\r\nthat the putative domains REJd3 and REJd4 likely do not form mechanically stable folds. Our experimental approach opens a new\r\nway to systematically study the effects of disease-causing mutations on the structure and mechanical properties of the REJ module\r\nof PC1.
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