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J. Bacteriol. doi:10.1128/JB.01621-07
Copyright (c) 2007, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Mesaconyl-Coenzyme A Hydratase, a New Enzyme of Two Central Carbon Metabolic Pathways in Bacteria

Mikrobiologie, Fakultät für Biologie, Universität Freiburg, Freiburg, Germany, and Pharmazeutische und Medizinische Chemie, Fakultät für Chemie, Pharmazie und Geowissenschaften, Universität Freiburg, Freiburg, Germany

^* To whom correspondence should be addressed. Email: georg.fuchs{at}biologie.uni-freiburg.de.

	Abstract

The coenzyme A (CoA) activated C₅-dicarboxylic acids mesaconyl-CoA and -methylmalyl-CoA play a role in two as yet not completely resolved central carbon metabolic pathways in bacteria. First, these compounds are intermediates in the 3-hydroxypropionate cycle for autotrophic CO₂ fixation in Chloroflexus aurantiacus, a phototrophic green non-sulfur bacterium. Second, mesaconyl-CoA and -methylmalyl-CoA are intermediates in the ethylmalonyl-CoA pathway for acetate assimilation in various bacteria, e.g. in Rhodobacter sphaeroides, Methylobacterium extorquens, or Streptomyces species. In both cases mesaconyl-CoA hydratase was postulated to catalyze the interconversion of mesaconyl-CoA and -methylmalyl-CoA.

The putative genes coding for this enzyme in C. aurantiacus and R. sphaeroides were cloned, heterologously expressed in Escherichia coli, and the proteins were purified and studied. The recombinant homodimeric 80 kDa proteins catalyzed the reversible dehydration of erythro--methylmalyl-CoA to mesaconyl-CoA with rates of 1,300 µmol min^-1 (mg protein)^-1. Genes coding for similar enzymes with two (R)-enoyl-CoA hydratase domains are present in the genomes of Roseiflexus, Methylobacterium, Hyphomonas, Rhodospirillum, Xanthobacter, Caulobacter, Magnetospirillum, Jannaschia, Sagittula, Parvibaculum, Stappia, Oceanicola, Loktanella, Silicibacter, Roseobacter, Roseovarius, Dinoroseobacter, Sulfitobacter, Paracoccus, and Ralstonia species. A similar, yet distinct class of enzymes containing only one hydratase domain was found in various other bacteria such as Streptomyces species. The role of this widely distributed new enzyme is discussed.