NDLI: What is the trigger mechanism for the reversal of electron flow in oxygen-tolerant [NiFe] hydrogenases?

Content Provider	Royal Society of Chemistry (RSC)
Author	Dance, Ian
Copyright Year	2015
Abstract	The [NiFe] hydrogenases use an electron transfer relay of three FeS clusters – proximal, medial and distal – to release the electrons from the principal reaction, H2 → 2H+ + 2e−, that occurs at the Ni–Fe catalytic site. This site is normally inactivated by O2, but the subclass of O2-tolerant [NiFe] hydrogenases are able to counter this inactivation through the agency of an unusual and unprecedented proximal cluster, with composition [Fe4S3(Scys)6], that is able to transfer two electrons back to the Ni–Fe site and effect crucial reduction of O2-derived species and thereby reactivate the Ni–Fe site. This proximal cluster gates both the direction and the number of electrons flowing through it, and can reverse the normal flow during O2 attack. The unusual structures and redox potentials of the proximal cluster are known: a structural change in the proximal cluster causes changes in its electron-transfer potentials. Using protein structure analysis and density functional simulations, this paper identifies a closed protonic system comprising the proximal cluster, some contiguous residues, and a proton reservoir, and proposes that it is activated by O2-induced conformational change at the Ni–Fe site. This change is linked to a key histidine residue which then causes protonation of the proximal cluster, and migration of this proton to a key μ3-S atom. The resulting SH group causes the required structural change at the proximal cluster, modifying its redox potentials, and leads to the reversed electron flow back to the Ni–Fe site. This cycle is reversible, and the protons involved are independent of those used or produced in reactions at the active site. Existing experimental support for this model is cited, and new testing experiments are suggested.
Starting Page	1433
Ending Page	1443
Page Count	11
File Format	HTM / HTML PDF
ISSN	20416520
Volume Number	6
Issue Number	2
Journal	Chemical Science
DOI	10.1039/c4sc03223c
Language	English
Publisher	Royal Society of Chemistry
Access Restriction	Subscribed
Subject Keyword	Oxygen Histidine Active site Redox Proton Pressure vessel Scys Protein structure
Content Type	Text
Resource Type	Article
Subject	Chemistry

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