Effects of Mutating Trp42 Residue on γD-Crystallin Stability

Oligomerization and aggregation of gamma D-crystallins (H gamma DC) in the eye lens is one of the main causes of cataract development. To date, several congenital mutations related to this protein are known to promote the formation of aggregates. Previous studies have demonstrated that mutations in W42 residue of H gamma DC lead to the generation of partially unfolded intermediates that are more prone to aggregate. To understand the role of W42 in the stability of H gamma DC, we performed alchemical free-energy calculations and all-atom molecular dynamics simulations of different W42 mutant models. Our results suggest that substitution of W42 by small size and/or polar residues promotes H gamma DC denaturation due to the entry of water molecules into the hydrophobic core of the N-terminal domain. Similar behavior was observed in the C-terminal domain of H gamma DC when mutating the W130 residue located in a homologous position. Moreover, the exposure of the hydrophobic core residues could lead to the formation of aggregation-prone partially unfolded species. Overall, this study takes a step toward understanding the role of H gamma DC in cataract development.