Molecular characterization of the 1,3-propanediol (1,3-PD) operon of Clostridium butyricum

Abstract

The genes encoding the 1,3-propanediol (1,3-PD) operon of Clostridium butyricum VPI1718 were characterized from a molecular and a biochemical point of view. This operon is composed of three genes, dhaB1, dhaB2, and dhaT. When grown in a vitamin B12-free mineral medium with glycerol as carbon source, Escherichia coli expressing dhaB1, dhaB2, and dhaT produces 1,3-PD and high glycerol dehydratase and 1,3-PD dehydrogenase activities. dhaB1 and dhaB2 encode, respectively, a new type of glycerol dehydratase and its activator protein. The deduced proteins DhaB1 and DhaB2, with calculated molecular masses of 88,074 and 34,149 Da, respectively, showed no homology with the known glycerol dehydratases that are all B12 dependent but significant similarity with the pyruvate formate lyases and pyruvate formate lyases activating enzymes and their homologues. The 1,158-bp dhaT gene codes for a 1,3-PD dehydrogenase with a calculated molecular mass of 41,558 Da, revealing a high level of identity with other DhaT proteins from natural 1,3-PD producers. The expression of the 1,3-PD operon in C. butyricum is regulated at the transcriptional level, and this regulation seems to involve a two-component signal transduction system DhaAS͞DhaA, which may have a similar function to DhaR, a transcriptional regulator found in other natural 1,3-PD producers. The discovery of a glycerol dehydratase, coenzyme B12 independent, should significantly influence the development of an economical vitamin B12-free biological process for the production of 1,3-PD from renewable resources.

Pyruvate Formate-lyase and a Novel Route of Eukaryotic ATP Synthesis in Chlamydomonas Mitochondria

“…The inferred PFL amino acid sequence shares extensive similarity with glycyl radical enzymes, an emerging class of anaerobic enzymes. These enzymes use a radical chemistry for carbon-carbon bond formation or cleavage (33)(34)(35). Fig.…”

Structural basis for glycyl radical formation by pyruvate formate-lyase activating enzyme

“…Because of their oxygen-sensitive nature, GREs (11)(12)(13)(14) are proposed to have evolved before the appearance of oxygen in the atmosphere, and some speculate that class III RNR may be a truly ancient enzyme (15) because the ancestral RNR was likely involved in the conversion of RNA-to DNA-based life (16). Unlike RNR, which converts ribonucleotides to deoxyribonucleotides, PFL is a central metabolic enzyme that converts pyruvate and CoA to acetyl-CoA and formate (17).…”

1,2-Propanediol Dehydration in Roseburia inulinivorans

“…At the present time the only structural information available for any GRE-type dehydratase is that of the glycerol dehydratase from Clostridium butyricum (CbGD) (3,16) . The presence of a homologous 1,2-propandiol dehydratase in Roseburia inulinivorans was proposed based on genomic and metabolic analyses of the organism (17).…”