Conformational dynamics study on human γS-crystallin as an efficient route to childhood blindness

Single point mutants of human γS-crystallin cause dominant congenital cataracts, a recent one of which involves the substitution of highly conserved glycine at 57th position with a bulkier tryptophan. Our high-resolution 3D structure of this G57W mutant (abbreviated hereafter as γS-G57W), reported recently revealed site-specific structural perturbations with higher aggregation and lower stability compared to its wild-type; a structural feature associated with important functional and therapeutic consequences. In this communication, we report for the first time, residue resolved conformational dynamics in both γS-WT and γS-G57W using solution NMR spectroscopy, and suggest how these differences could crucially affect the biochemistry of the mutant. Guided by our critical structural investigations, extensive conformational dynamics and biophysical studies presented here show that loss of structural stability arises from enhanced dynamics in Greek key motif 2 inducing flexibility in the N-terminal domain as opposed to its structurally unperturbed C-terminal counterpart. NMR spectral density correlations and internal dynamics comparisons with the wild-type suggest that the overall thermodynamic instability propagates from the mutated N-terminal β4-β5 loop providing a residue level understanding of the structural changes associated with this early onset of lens opacification. Our results highlight the vital role of conserved Greek key motifs in conferring structural stability to crystallins and provide crucial molecular insights into crystallin aggregation in the eye lens, which triggers cataract formation in children. Overall, this critical study provides a residue level understanding of how conformational changes affect the structure and function of crystallins in particular and proteins in general, during health and disease.