Tuning Catalytic Bias of Hydrogen Gas Producing Hydrogenases

Abstract

Hydrogenases display a wide range of catalytic rates and biases in reversible hydrogen gas oxidation catalysis. The interactions of the iron−sulfur-containing catalytic site with the local protein environment are thought to contribute to differences in catalytic reactivity, but this has not been demonstrated. The microbe Clostridium pasteurianum produces three [FeFe]-hydrogenases that differ in "catalytic bias" by exerting a disproportionate rate acceleration in one direction or the other that spans a remarkable 6 orders of magnitude. The combination of high-resolution structural work, biochemical analyses, and computational modeling indicates that protein secondary interactions directly influence the relative stabilization/destabilization of different oxidation states of the active site metal cluster. This selective stabilization or destabilization of oxidation states can preferentially promote hydrogen oxidation or proton reduction and represents a simple yet elegant model by which a protein catalytic site can confer catalytic bias.

The Hydricity and Reactivity Relationship in [ FeFe ]-hydrogenases

“…7,8 Transition metals are critical to biological energy transformation reactions and are found in many enzyme active sites, including the FeMo cofactor in nitrogenase, leading to reduction of dinitrogen to ammonia, 9 the tungsten-or molybdenum-containing formate dehydrogenases, which reversibly reduce CO 2 to formate, 10 methyl coenzyme reductase, 11 which catalyzes the reduction of CH 3 -S-CoM to methane, and hydrogenases, which catalyze reversible H 2 activation chemistry. 12,13 For the latter, striking differences in preferences for H 2 oxidation or H 2 production reactivity for a series of three unique [FeFe]hydrogenases from Clostridium pasteurianum has been shown. 12,14 Each [FeFe]-hydrogenase incorporates a organometallic, iron-sulfur rich H cluster ( Fig.…”

“…12,13 For the latter, striking differences in preferences for H 2 oxidation or H 2 production reactivity for a series of three unique [FeFe]hydrogenases from Clostridium pasteurianum has been shown. 12,14 Each [FeFe]-hydrogenase incorporates a organometallic, iron-sulfur rich H cluster ( Fig. 1), with additional iron-sulfur clusters, or F clusters, that can provide electron transfer functions.…”

New Approaches to an Old Problem: Original Techniques in [FeFe]-hydrogenase Research

“…Here, the difference between Fe(II)-Fe(I) in Hox and Fe(I)-Fe(I) in Hsred is ~50 cm -1 29. It should be mentioned that a similar low frequency peak has been assigned to Hox in CpII 47. Infrared signature of Hox for different Group A [FeFe]-hydrogenases.…”

“…At the [4Fe-4S] cluster, amino acid exchanges 45 and protonation differences 46 have been shown to affect the electrochemical properties of the H-cluster, and a similar effect was discussed for the orientation of a conserved serine (S2 in Figure 4). 47 Finally, a methionine residue below the Hcluster was suggested to promote the release of µCO into a semi-bridging or terminal position upon reduction of the diiron site (M1 in Figure 4). 29 The conservation of this methionine is a key difference between groups A/B and C/D and has important implications for the catalytic mechanism (Chapter 4).…”

“…[122][123][124] This is in agreement with a recent study by Artz et al comparing cryogenic CpI crystal structures solved with both synchrotron radiation and the free electron laser (XFEL) light source at Stanford. 47 The authors were able to quantify the extent of photoreduction suggesting that in the presence of strong reductant up to 50% of CpI was found in a "more reduced conformation" featuring the H-cluster in a µCO geometry. The influence of temperature is discussed in the next chapter.…”