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).