[Proton migration in a stack of tyrosine molecules induced by Mg(2+) ion and electric field. Mathematical model]

Quantum chemistry methods (ab initio, RHF + MP2(FULL), 6-31G** basis set) were used to study proton migration in tyrosine stacks mimicking the proton channel in tubulin and other proteins. When bound to guanosine-5'-triphosphate, Mg2+ favors the dissociation of water in its first coordination shell, thus initiating subsequent proton shifts in the tyrosine chain composed of spatially remote tyrosine residues of tubulin. The process appears to be thermodynamically allowed, delta G298 < 0, with a potential barrier along the proton shift of no more than 0.75 kcal/mol. The exposure to external electrical field of low intensity, which simulates the electric properties of tubulin, promotes proton migration over long distances.