Density Functional Theory Calculations to Investigate the Role Played by an Aspartate Dyad in Hsp60-Catalyzed ATP Hydrolysis

Adenosine 5′-triphosphate
(ATP) hydrolysis is one of the
most significant reactions in biochemistry. In chaperone proteins,
energy released by hydrolysis enables them to carry out their function
and help other proteins (called “clients”) to fold into
their functional form. Here, we run Density Functional Theory calculations
on three cluster models of the Hsp60 active site extracted from our
previous molecular dynamics simulations of the 14-meric Hsp60 double-ring
complex: our aim is to qualitatively investigate the mechanisms of
ATP hydrolysis in different scenarios where the chaperone closes a
dyad composed of catalytic aspartates Asp50 and Asp397. Since dyad
closure raises Asp pKa values and increases
likelihood of protonation, we modeled the active site both in the
presence and absence of a proton. Comparison of reaction barriers
suggests that hydrolysis is favored when aspartates become deprotonated,
explaining increased ATPase activity observed in V72I mutant Hsp60
(known to favor dyad closure).