Kinesin ATP Hydrolysis Requires Proton Tunneling within the Zundel Cation and a Second Proton Transfer

Occurring between hydrogen-bonded networks of polar residues and water molecules, proton transfer reactions are essential in energy conversion, transduction, storage biological systems. Here, we determine the contribution to acceleration ATP hydrolysis kinesins. A novel two-water cluster, or a Zundel cation, was observed be salt bridge kinesin motor protein active site. Solvent kinetic isotope experiments showed abstraction from cluster commits catalysis. The magnitude positive effect (KIE) Arrhenius temperature dependence confirmed unanticipated, non-classical description involving cation Site-directed mutants verified that salt-bridge required for solvent KIE detection. Lastly, by examining varying 1H2O:2H2O ratio on catalysis, our inventory data quantified two transfers rate-limiting step hydrolysis. These support model mechanotransduction accounts reactions. first transfer, waters allow nucleophilic attack γ-phosphate ATP, has tunneling component. Experimental determination quantum mechanical event, which particle through reaction barrier, offers an alternate explanation classical transition-state second measured is likely separated molecules bridge. We conclude proteins can involve tunneling, control coordinate, strong anharmonic couplings many degrees freedom mechanotransduction.