Cataract-Associated New Mutants S175G/H181Q of beta Beta 2-Crystallin and P24S/S31G of gamma D-Crystallin Are Involved in Protein Aggregation by Structural Changes

Abstract

beta/gamma-Crystallins, the main structural protein in human lenses, have highly stable structure for keeping the lens transparent. Their mutations have been linked to cataracts. In this study, we identified 10 new mutations of beta/gamma-crystallins in lens proteomic dataset of cataract patients using bioinformatics tools. Of these, two double mutants, S175G/H181Q of beta Beta 2-crystallin and P24S/S31G of gamma D-crystallin, were found mutations occurred in the largest loop linking the distant beta-sheets in the Greek key motif. We selected these double mutants for identifying the properties of these mutations, employing biochemical assay, the identification of protein modifications with nanoUPLC-ESI-TOF tandem MS and examining their structural dynamics with hydrogen/deuterium exchange-mass spectrometry (HDX-MS). We found that both double mutations decrease protein stability and induce the aggregation of beta/gamma-crystallin, possibly causing cataracts. This finding suggests that both the double mutants can serve as biomarkers of cataracts.