Ultrahigh-resolution study on Pyrococcus abyssi rubredoxin: II. Introduction of an O-H...Sgamma-Fe hydrogen bond increased the reduction potential by 65 mV.

The effect of D-H...S(gamma)-Fe hydrogen bonding on the reduction potential of rubredoxin was investigated by the introduction of an O-H...S(gamma)-Fe hydrogen bond on the surface of Pyrococcus abyssi rubredoxin. The formation of a weak hydrogen bond between Ser44-O(gamma) and Cys42-S(gamma) in mutant W4L/R5S/A44S increased the reduction potential by 56 mV. When side effects of the mutation were taken into account, the contribution of the additional cluster hydrogen bond to the reduction potential was estimated to be +65 mV. The structural analysis was based on ultrahigh-resolution structures of oxidized P. abyssi rubredoxin W4L/R5S and W4L/R5S/A44S refined to 0.69 and 0.86 A, respectively.