Journal
PROTEIN SCIENCE
Volume 19, Issue 1, Pages 131-140Publisher
WILEY
DOI: 10.1002/pro.296
Keywords
non-native interaction; eye cataracts; molecular dynamics; beta-sheet protein folding
Categories
Funding
- NIH [GM17980, EY015834]
- NATIONAL EYE INSTITUTE [R01EY015834] Funding Source: NIH RePORTER
- NATIONAL INSTITUTE OF GENERAL MEDICAL SCIENCES [R37GM017980, R01GM017980] Funding Source: NIH RePORTER
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Human age-onset cataracts are believed to be caused by the aggregation of partially unfolded or covalently damaged lens crystallin proteins; however, the exact molecular mechanism remains largely unknown. We have used microseconds of molecular dynamics simulations with explicit solvent to investigate the unfolding process of human lens gamma D-crystallin protein and its isolated domains. A partially unfolded folding intermediate of gamma D-crystallin is detected in simulations with its C-terminal domain (C-td) folded and N-terminal domain (N-td) unstructured, in excellent agreement with biochemical experiments. Our simulations strongly indicate that the stability and the folding mechanism of the N-td are regulated by the interdomain interactions, consistent with experimental observations. A hydrophobic folding core was identified within the C-td that is comprised of a and b strands from the Greek key motif 4, the one near the domain interface. Detailed analyses reveal a surprising non-native surface salt-bridge between Glu135 and Arg142 located at the end of the ab folded hairpin turn playing a critical role in stabilizing the folding core. On the other hand, an in silico single E135A substitution that disrupts this non-native Glu135-Arg142 salt-bridge causes significant destabilization to the folding core of the isolated C-td, which, in turn, induces unfolding of the N-td interface. These findings indicate that certain highly conserved charged residues, that is, Glu135 and Arg142, of gamma D-crystallin are crucial for stabilizing its hydrophobic domain interface in native conformation, and disruption of charges on the gamma D-crystallin surface might lead to unfolding and subsequent aggregation.
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