ATP hidrolizinin HSP70 şaperon proteini tarafından katalizlenmesi

Molecular chaperone proteins assist the newly synthesized proteins to fold into the native structure. Many chaperone proteins are also heat shock proteins, which assists refolding of the proteins denatured under stress conditions, with Hsp70 being one of them. In this study, the ATP hydrolysis mechanism of Hsp70 has been investigated using the QM/MM ONIOM method with M06-2X for the QM part and the AMBER force field for the MM part. Two main models were created depending on the protonation states of D201. Particular attention has been paid to the role of K70 because this residue is crucial for ATP hydrolysis. In addition, the possibility that K70 is involved in acid catalysis has been investigated. Other candidates for acid catalysis were D194 and a water molecule between Mg2+ and K+ and E171 is used as a base candidate. In the crystallographic structure, a Mg2+ ion is coordinated to the beta-phosphate group. It is suggested that shift of Mg2+ to a position between the beta- and gamma-phosphate groups. This mechanism is also tested. Our results showed that proton transfer to ATP occurs with nucleophilic water directly attacking the ATP and acid-base catalysis seems unlikely. Suggested mechanism about the shift of Mg2+ is also unlikely. In the models with a deprotonated D201, Pi tends to donate a proton to a nearby water or E171, which suggests that E171 can accept a proton after product formation. And when a proton is deleted on Pi, Mg2+ shift between the two phosphate groups is energetically favorable.