Structural and functional characterization of D109H and R69C mutant versions of human αB-crystallin: The biochemical pathomechanism underlying cataract and myopathy development

In human alpha B-crystallin (alpha B-Cry), the highly conserved residues arginine 69 (R69) and aspartate 109 (D109) are located within a critical motif of alpha-crystallin domain (ACD), contributing to the subunit interactions and oligomeric assembly. Recently, two missense mutations (R69C and D109H) in human alpha B-Cry have been reported to cause congenital cataract and myopathy disorders. We used various spectroscopic techniques, dynamic light scattering (DLS), small-angle X-ray scattering (SAXS), gel electrophoresis and transmission electron microscopy (TEM) to show how these mutations cause significant changes in structure, amyloidogenic feature and biological function of human alpha B-Cry. These pathogenic mutations resulted in the important alterations of the secondary, tertiary and oligomeric (quaternary) structures of human alpha B-Cry. The missense mutations were also capable to significantly increase the amyloidogenic propensity of human alpha B-Cry and to diminish the chaperone-like activity of this protein. The above mentioned changes were observed more noticeably after D109H mutation. The detrimental effects of D109H mutation may be due to the loss of salt bridge with R120 in the dimeric interface, flagging the anti-aggregation ability of alpha B-Cry chaperone. In conclusion, the R69C and D109H mutations displayed a significant damaging effect on the structure and chaperone function of human alpha B-Cry which could be considered as their biochemical pathomechanisms in development of congenital cataract and myopathy disorders. (C) 2019 Elsevier B.V. All rights reserved.