Outer-sphere effects on the O₂ sensitivity, catalytic bias and catalytic reversibility of hydrogenases

Abstract

The comparison of homologous metalloenzymes, in which the same inorganic active site is surrounded by a variable protein matrix, has demonstrated that residues that are remote from the active site...

Catalytic Bias and Redox-Driven Inactivation of the Group B FeFe Hydrogenase CpIII

“…22 These three prototypical enzymes have been the focus of most of the biophysical studies of FeFe hydrogenases, but atypical hydrogenases have recently been characterized, and unexpected features have emerged. 13 For example, the group A "CbA5H″ FeFe hydrogenase from Clostridium beijerinckii (Cb) is protected from oxygen damage by the binding to the distal Fe ion of the conserved cysteine that is the first proton relay; this binding can occur because nonconserved residues that are remote from the active site make the protein loop that bears the cysteine residue more flexible than in other hydrogenases. 4,12,14 In the group D FeFe hydrogenase from Thermoanaerobacter mathranii, protons are transferred along a pathway that is entirely distinct from that of prototypical hydrogenases, 15,16 and catalysis is 'irreversible', that is, H 2 oxidation and production only occur at the price of a large thermodynamic driving force.…”

“…An earlier, structural classification is based on the number of accessory FeS clusters: zero (M1), two (M2), or four clusters (M3), as exemplified by the three group A1 enzymes from Chlamydomonas reinhardtii (Cr HydA1), Desulfovibrio desulfuricans, and Clostridium pasteurianum (CpI), respectively . These three prototypical enzymes have been the focus of most of the biophysical studies of FeFe hydrogenases, but atypical hydrogenases have recently been characterized, and unexpected features have emerged …”