Hydrogen bonding affects the [NiFe] active site of Desulfovibrio vulgaris Miyazaki F hydrogenase: a hyperfine sublevel correlation spectroscopy and density functional theory study

Pulse electron paramagnetic resonance and hyperfine sublevel correlation spectroscopy have been used to investigate nitrogen coordination of the active site of NiFe] hydrogenase of Desulfovibrio vulgaris Miyazaki F in its oxidized "ready" state. The obtained (14)N hyperfine (A = +1.32, +1.32, +2.07] MHz) and nuclear quadrupole (e(2)qQ/h = -1.9 MHz, eta = 0.37) coupling constants were assigned to the N(epsilon) of a highly conserved histidine (His88) by studying a hydrogenase preparation in which the histidines were (15)N labeled. The histidine is hydrogen-bonded via its N(epsilon)-H to the nickel-coordinating sulfur of a cysteine (Cys549) that carries an appreciable amount of spin density. Through the hydrogen bond a small fraction of the spin density ( approximately 1%) is delocalized onto the histidine ring giving rise to an isotropic (14)N hyperfine coupling constant of about 1.6 MHz. These conclusions are supported by density functional calculations. The measured (14)N quadrupole coupling constants are related to the polarization of the N(epsilon)-H bond, and the respective hydrogen bond can be classified as being weak.