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PubMed1998

Molecular cloning, sequencing and characterization of the genes for adenosylcobalamin-dependent diol dehydratase of Klebsiella pneumoniae.

Klebsiella pneumoniae and some of the other Enterobacteriaceae form both diol dehydratase and glycerol dehydratase in response to growth substrates. To compare these enzymes produced by the same bacterium, the pdd genes of K. pneumoniae encoding adenosylcobalamin-dependent diol dehydratase were cloned and sequenced. The sequential three open reading frames (pddA, pddB, and pddC genes) encoded polypeptides of 554, 228, and 174 amino acid residues with predicted molecular weights of 60,379(alpha), 24,401(beta), and 19,489(gamma), respectively. The deduced amino acid sequences of the subunits were 84-100% and 54-71% identical with those reported for diol dehydratases and glycerol dehydratases, respectively.

Amino Acid Sequence↗
PubMed2005

The N-terminal regions of beta and gamma subunits lower the solubility of adenosylcobalamin-dependent diol dehydratase.

Adenosylcobalamin-dependent diol dehydratase is one of essential components of carboxysome-like polyhedral bodies. It exists as a heterohexamer (alphabetagamma)(2), and its activity is recovered in a precipitant fraction of Klebsiella oxytoca and overexpressing Escherichia coli cells. Limited proteolysis of the enzyme with trypsin converted the enzyme into a highly soluble form without loss of enzyme activity. The N-terminal amino acid sequencing of the enzyme thus solubilized indicated that the N-terminal 20 and 16 amino acid residues had been removed from the beta and gamma subunits, respectively. Mutant enzymes with the same N-terminal truncations of either or both of the beta and gamma subunits were expressed on a high level in E. coli cells. All the mutant enzymes obtained were expressed in a soluble, active form. These results indicate that the N-terminal regions of the beta and gamma subunits lower the solubility of diol dehydratase. The mutant enzyme with the N-terminal truncations of both beta and gamma subunits was essentially indistinguishable in catalytic properties from recombinant wild-type enzyme or the enzyme purified from K. oxytoca in a soluble form.

Amino Acid Sequence↗
PubMed1987

Re-investigation of the protein structure of coenzyme B12-dependent diol dehydrase.

We have purified diol dehydrase, an adenosylcobalamin-dependent enzyme, from Klebsiella pneumoniae by two different procedures to re-investigate its protein structure; one including its extraction with detergent from the membrane fraction, and the other consisting of only chromatographic separations of the soluble fraction. The enzyme preparations obtained by these two methods were different in the subunit structure, but both are identical in molecular weight, and in-enzymological and immunochemical properties. In addition, the enzyme preparation obtained from the membrane fraction dissociated reversibly into two dissimilar protein components (F and S) in the absence of substrate, as did the preparation from the soluble fraction. Although the subunit multiplicity of component S might be partly due to proteolytic cleavage during the enzyme purification as revealed by limited digestion with trypsin, component F is not a product of proteolytic cleavage of component S, but a primordial and essential constituent of the enzyme.

Cell Membrane↗
PubMed1982

The mechanism of in sutu reactivation of glycerol-inactivated coenzyme B12-dependent enzymes, glycerol dehydratase and diol dehydratase.

In the previous paper (S. Honda, T. Toraya, and S. Fukui, J. Bacteriol., 143, 1458-1465 (1980)), we reported that the glycerol-inactivated holoenzymes of adenosylcobalamin-dependent glycerol dehydratase and diol dehydratase are rapidly and continually reactivated in toluene-treated cells (in situ) by adenosine 5'-triphosphate (ATP) and divalent metal ions in the presence of free adenosylcobalamin. To elucidate the mechanism of this in situ reactivation, the nature of the binding of various irreversible cobalamin inhibitors to the dehydratases in situ was investigated. In the presence of ATP and Mn2+, enzyme-bound hydroxocobalamin, cyanocobalamin and methylcobalamin were rapidly displaced by added adenosylcobalamin. Without ATP and Mn2+, such displacement did not take place. In contrast, enzyme-bound adeninylbutylcobalamin and adenosylethylcobalamin were essentially not displaceable by the free coenzyme even in the presence of ATP and Mn2+. Inosylcobalamin was a very weak inhibitor irrespective of the presence of ATP and Mn2+. These results indicate that the relative affinity of the enzymes in situ for the cobalamins with simple Co beta ligands was markedly lowered in the presence of ATP and Mn2+, whereas that for the cobalamins with adenine-containing ligands was not. When the glycerol-inactivated holoenzymes in situ were dialyzed against a buffer containing ATP and Mg2+, the inactivated coenzyme moiety dissociated from the enzymes leaving apoproteins. Kinetic evidence was also obtained with the dehydratases in situ that continual displacement of the inactivated coenzyme moiety by adenosylcobalamin takes place during the glycerol dehydration reaction in the presence of ATP and Mn2+. Since the adenosyl group of the bound coenzyme is irreversibly removed from the cobalamin moiety during inactivation by glycerol, all of these data constitute clear evidence that the inactivated holo-dehydratases are reactivated in situ in the presence of ATP and Mn2+ by displacement of the modified coenzyme moiety by free intact adenosylcobalamin (i.e. selective B12-exchange mechanism).

Adenosine Triphosphate↗
PubMed1993

Importance of the nucleotide loop moiety coordinated to the cobalt atom of adenosylcobalamin for coenzymic function in the diol dehydrase reaction.

Three analogs of adenosylcobalamin were synthesized and their coenzymic properties in the diol dehydrase reaction were studied. Neither adenosylcobinamide nor adenosylcobinamide phosphate was active as coenzyme and showed very low affinity for apoenzyme, irrespective of the presence of nucleotide loop fragments, such as 5,6-dimethylbenzimidazole, alpha-D-ribazole, or alpha-D-ribazole-3'-phosphate. The coordination of pyridine to the cobalt atom neither confers the coenzymic function upon adenosylcobinamide nor strengthens the inhibitory effect of cyanoaquacobinamide and methylcobinamide significantly. The analog of adenosylcobalamin in which the N-3 position of 5,6-dimethylbenz-imidazole is methylated was also not active as coenzyme and showed very low affinity for apoenzyme. Since 3,5,6-trimethylbenzimidazole in this analog is no longer coordinated to the cobalt atom, these results show that at least a part of the nucleotide loop moiety coordinated to the cobalt atom of adenosylcobalamin is essential for tight binding to the apoenzyme and therefore for manifestation of coenzymic function.

Binding Sites↗