title: Characterization and mechanism of action of a reactivating factor for adenosylcobalamin-dependent glycerol dehydratase.
abstract: Adenosylcobalamin-dependent glycerol dehydratase undergoes mechanism-based inactivation by its physiological substrate glycerol. We identified two genes (gdrAB) of Klebsiella pneumoniae for a glycerol dehydratase-reactivating factor (Tobimatsu, T., Kajiura, H., Yunoki, M., Azuma, M., and Toraya, T. (1999) J. Bacteriol. 181, 4110-4113). Recombinant GdrA and GdrB proteins formed a tight complex of (GdrA)(2)(GdrB)(2), which is a putative reactivating factor. The purified factor reactivated the glycerol-inactivated and O(2)-inactivated glycerol dehydratases as well as activated the enzyme-cyanocobalamin complex in vitro in the presence of ATP, Mg(2+), and adenosylcobalamin. The factor mediated the exchange of the enzyme-bound, adenine-lacking cobalamins for free, adenine-containing cobalamins in the presence of ATP and Mg(2+) through intermediate formation of apoenzyme. The factor showed extremely low ATP-hydrolyzing activity and formed a tight complex with apoenzyme in the presence of ADP. Incubation of the enzyme-cyanocobalamin complex with the reactivating factor in the presence of ADP brought about release of the enzyme-bound cobalamin. The resulting tight inactive complex of apoenzyme with the factor dissociated upon incubation with ATP, forming functional apoenzyme and a low affinity form of factor. Thus, it was established that the reactivation of the inactivated holoenzymes takes place in two steps: ADP-dependent cobalamin release and ATP-dependent dissociation of the apoenzyme-factor complex. We propose that the glycerol dehydratase-reactivating factor is a molecular chaperone that participates in reactivation of the inactivated enzymes.
authors.affiliation: Department of Bioscience and Biotechnology, Faculty of Engineering, Okayama University, Tsushima-naka, Okayama 700-8530, Japan.
authors.forename: H
authors.initials: H
authors.lastname: Kajiura
authors.forename: K
authors.initials: K
authors.lastname: Mori
authors.forename: T
authors.initials: T
authors.lastname: Tobimatsu
authors.forename: T
authors.initials: T
authors.lastname: Toraya
mesh_terms: D000244:Adenosine Diphosphate / Q000378:metabolism; D000251:Adenosine Triphosphatases / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism; D003038:Cobamides / Q000737:chemistry / Q000378:metabolism*; D004591:Electrophoresis, Polyacrylamide Gel; D004789:Enzyme Activation; D004926:Escherichia coli / Q000201:enzymology; D006836:Hydro-Lyases / Q000737:chemistry* / Q000378:metabolism; D008274:Magnesium / Q000378:metabolism; D008956:Models, Chemical; D010957:Plasmids / Q000378:metabolism; D011485:Protein Binding; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D013997:Time Factors; D014805:Vitamin B 12 / Q000737:chemistry / Q000378:metabolism
chemical_list: D003038:Cobamides; D011994:Recombinant Proteins; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D000251:Adenosine Triphosphatases; D006836:Hydro-Lyases; C020671:glycerol dehydratase; C000913:cobamamide; D008274:Magnesium; D014805:Vitamin B 12