Identification and Characterization of Oxalate Oxidoreductase, a Novel Thiamine Pyrophosphate-dependent 2-Oxoacid Oxidoreductase That Enables Anaerobic Growth on Oxalate

Elizabeth Pierce,Donald F Becker,Stephen W Ragsdale

doi:10.1074/jbc.m110.155739

Elizabeth Pierce, Donald F Becker + Show 1 more

Open Access

https://doi.org/10.1074/jbc.m110.155739

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Abstract

Moorella thermoacetica is an anaerobic acetogen, a class of bacteria that is found in the soil, the animal gastrointestinal tract, and the rumen. This organism engages the Wood-Ljungdahl pathway of anaerobic CO(2) fixation for heterotrophic or autotrophic growth. This paper describes a novel enzyme, oxalate oxidoreductase (OOR), that enables M. thermoacetica to grow on oxalate, which is produced in soil and is a common component of kidney stones. Exposure to oxalate leads to the induction of three proteins that are subunits of OOR, which oxidizes oxalate coupled to the production of two electrons and CO(2) or bicarbonate. Like other members of the 2-oxoacid:ferredoxin oxidoreductase family, OOR contains thiamine pyrophosphate and three [Fe(4)S(4)] clusters. However, unlike previously characterized members of this family, OOR does not use coenzyme A as a substrate. Oxalate is oxidized with a k(cat) of 0.09 s(-1) and a K(m) of 58 μM at pH 8. OOR also oxidizes a few other 2-oxoacids (which do not induce OOR) also without any requirement for CoA. The enzyme transfers its reducing equivalents to a broad range of electron acceptors, including ferredoxin and the nickel-dependent carbon monoxide dehydrogenase. In conjunction with the well characterized Wood-Ljungdahl pathway, OOR should be sufficient for oxalate metabolism by M. thermoacetica, and it constitutes a novel pathway for oxalate metabolism.

Highlights

Moorella thermoacetica is a strictly anaerobic Gram-positive acetogenic bacterium
This paper describes the characterization of the oxalateinduced enzyme, oxalate oxidoreductase (OOR)2 and demonstrates that it, unlike all previously characterized members of the thiamine pyrophosphate (TPP)-dependent 2-oxoacid: ferredoxin oxidoreductase family, does not require coenzyme A
Oxalate is an important metabolite that is produced in the soil and in the animal gastrointestinal tract, with elevated levels causing kidney stones

Summary

Introduction

Moorella thermoacetica is a strictly anaerobic Gram-positive acetogenic bacterium. Acetogens are commonly found in the soil, animal gastrointestinal tract, and the rumen and grow heterotrophically or autotrophically on many different electron donors. Daniel et al [14] found that oxalate-grown cells metabolize oxalate much more quickly than cells that had been grown on glucose, which is consistent with an oxalate induction mechanism [15] They showed that cell extracts from oxalate-grown cells could catalyze oxalate-dependent benzyl viologen reduction, that this activity was only slightly stimulated by coenzyme A, and that the electron acceptor specificity of oxalate oxidation was different than that of formate oxidation. They concluded that M. thermoacetica catabolizes oxalate by a CoA-independent mechanism that does not use formate as an intermediate. Coupling OOR to the Wood-Ljungdahl pathway allows anaerobic bacteria to generate energy by converting oxalate to acetyl-CoA

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