The βγ-crystallins: Native state stability and pathways to aggregation

Wild-type Human γD-crystallin Promotes Aggregation of Its Oxidation-mimicking, Misfolding-prone W42Q Mutant

“…Domain Swapping Models of Aggregation-Molecular dynamics simulations have suggested a swapping pathway via exchange of full globular domains in H␥D (46); however, genetic evidence suggests swapping at the N-terminal ␤-strands instead (14), and such a domain-swap mechanism is consistent with recent force spectroscopy measurements on an H␥D polyprotein. 3 That relatively high concentrations of WT are required to promote W42Q aggregation may be due to a relatively weak WT/mutant interaction or to only a small fraction of WT being "active" at any given time.…”

“…Weak attractive protein-protein interactions in WT ␥D crystallin have been inferred from dynamic light scattering (49). Although the aggregates themselves are likely to involve misfolding of the N-td, we note that the C-td of H␥D facilitates N-td folding (14). The N-td/C-td interaction contributes ϳ4.2 kcal/mol to the stability of the N-td in the WT protein (32).…”

“…The result is progressive increase in light scattering (lens turbidity) caused by aggregation; this is the basis of cataract disease, a major cause of blindness worldwide (12,13). No long range structure has been found in the cataractous aggregates (14), but disulfides and other covalent modifications are common (15,16). Reducing capacity of the lens core cytosol is lost during cataractogenesis (17).…”

“…The ␤-sheet rich H␥D monomer has a melting temperature of 82°C and aggregates only under nonphysiological conditions (20). More than 20 point mutations in conserved ␥-crystallin residues, particularly near the N-terminal ␤-strands, are linked to congenital cataract (14). Such mutations can generate conformational intermediates leading to aggregation (8,(21)(22)(23).…”

An Internal Disulfide Locks a Misfolded Aggregation-Prone Intermediate in Cataract-Linked Mutants of Human Gamma-D Crystallin

“…Passive chaperones, the α-crystallins, are present in lens, but their capacity declines with age, even as their substrates, the βγ-crystallins, accumulate destabilizing chemical modifications (13) due to a variety of environmental damage (17). The result is generation of partially unfolded intermediate conformational states and progressive increase in light scattering (lens turbidity) due to aggregation (18)(19)(20)(21). No long-range structure, amyloid or otherwise, has been found in the cataractous aggregates (22,23), except in certain rare congenital cases (24,25), but disulfide bonds and other covalent modifications are common (13,(26)(27)(28)(29).…”