Steered Molecular Dynamics Study of the Age-related Stiffening of the Crystalline Lens

αA-crystallin is a key component of the glassy solution of proteins that constitutes the mammalian lens. It contributes to the refractive and mechanical properties of the lens, and as a member of the small heat shock protein (sHSP) family of chaperones, plays a role in aggregate prevention. Age-dependent L- to D- racemization of amino acids in the sequence of the protein has been implicated in lens stiffening and cataract, and is suspected to interfere with the protein’s basic chaperone activity and structural features. This communication investigates the mechanical properties of bovine αA-crystallin and several of its (point) D-isomerized derivatives by way of Steered Molecular Dynamics simulation. In a series of induced unfolding experiments, an external pulling force is applied to the native protein and, independently, to three D-amino acid variants. A principal component-based technique is applied to extract dominant structural and mechanical features from the system variants. The D-isomerization of a single residue in the structure of αA-crystallin alters the protein’s unfolding pathway, and changes the mechanical properties of its inherent elements of (secondary) protein structure. The location of the D- substituted residue is critical to defining the extent and nature of the observed effects. The latter are expressed as divergence from the typical native induced unfolding pathway and altered structural element stiffnesses.