Crystal Structure of Quinohemoprotein Alcohol Dehydrogenase from Comamonas testosteroni: STRUCTURAL BASIS FOR SUBSTRATE OXIDATION AND ELECTRON TRANSFER

Arthur Oubrie,Henriëtte J Rozeboom,Kor H Kalk,Eric G Huizinga,Bauke W Dijkstra

doi:10.1074/jbc.m109403200

Arthur Oubrie, Henriëtte J Rozeboom + Show 3 more

Open Access

https://doi.org/10.1074/jbc.m109403200

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Abstract

Quinoprotein alcohol dehydrogenases are redox enzymes that participate in distinctive catabolic pathways that enable bacteria to grow on various alcohols as the sole source of carbon and energy. The x-ray structure of the quinohemoprotein alcohol dehydrogenase from Comamonas testosteroni has been determined at 1.44 A resolution. It comprises two domains. The N-terminal domain has a beta-propeller fold and binds one pyrroloquinoline quinone cofactor and one calcium ion in the active site. A tetrahydrofuran-2-carboxylic acid molecule is present in the substrate-binding cleft. The position of this oxidation product provides valuable information on the amino acid residues involved in the reaction mechanism and their function. The C-terminal domain is an alpha-helical type I cytochrome c with His(608) and Met(647) as heme-iron ligands. This is the first reported structure of an electron transfer system between a quinoprotein alcohol dehydrogenase and cytochrome c. The shortest distance between pyrroloquinoline quinone and heme c is 12.9 A, one of the longest physiological edge-to-edge distances yet determined between two redox centers. A highly unusual disulfide bond between two adjacent cysteines bridges the redox centers. It appears essential for electron transfer. A water channel delineates a possible pathway for proton transfer from the active site to the solvent.

Highlights

Quinoprotein alcohol dehydrogenases are redox enzymes that participate in distinctive catabolic pathways that enable bacteria to grow on various alcohols as the sole source of carbon and energy
Several x-ray structures have been reported of type I quinoprotein alcohol dehydrogenases (ADHs) (20 –24) and a soluble quinoprotein glucose dehydrogenase [25]. sGDH-inhibitor [26] and sGDHsubstrate [27] complexes have provided detailed insights into the dehydrogenation reaction
These data have clearly shown how sGDH and methanol dehydrogenases (MDHs) react with their substrates and, no information has so far been available to substantiate this hypothesis, it has been argued that the same mechanism operates in the other quinoprotein ADHs [29]

Summary

STRUCTURAL BASIS FOR SUBSTRATE OXIDATION AND ELECTRON TRANSFER*

The C-terminal domain is an ␣-helical type I cytochrome c with His608 and Met647 as heme-iron ligands This is the first reported structure of an electron transfer system between a quinoprotein alcohol dehydrogenase and cytochrome c. Quinoproteins are oxidoreductases that possess one of four different quinone compounds instead of nicotinamide or flavin cofactors (4 –7) They oxidize a wide variety of alcoholand amine-containing substrates to the corresponding aldehydes or ketones. A recent MDH structure revealed the presence of a PQQ intermediate in the catalytic mechanism [28] These data have clearly shown how sGDH and MDH react with their substrates and, no information has so far been available to substantiate this hypothesis, it has been argued that the same mechanism operates in the other quinoprotein ADHs [29].

RMS deviations from ideal geometry

EXPERIMENTAL PROCEDURES

RESULTS AND DISCUSSION