Intracellular D-(-)-3-hydroxybutyrate oligomer hydrolase (also known as 3HB-oligomer hydrolase 3HBOH) functions in the degradation of poly-3-hydroxybutyrate (PHB). It catalyses the hydrolysis of D(-)-3-hydroxybutyrate oligomers (3HB-oligomers) into 3HB-monomers.
Title: Roles of poly(3-hydroxybutyrate) depolymerase and 3HB-oligomer hydrolase in bacterial PHB metabolism Sugiyama A, Kobayashi T, Shiraki M, Saito T Ref: Curr Microbiol, 48:424, 2004 : PubMed
Many poly-3-hydroxybutyrate (PHB)-degrading enzymes have been studied. But biological roles of 3HB-oligomer hydrolases (3HBOHs) and how PHB depolymerases (PHBDPs) and 3HBOHs cooperate in PHB metabolism are not fully elucidated. In this study, several PHBDPs and 3HBOHs from three types of bacteria were purified, and their substrate specificity, kinetic properties, and degradation products were investigated. From the results, PHBDP and 3HBOH seemed to play a role in PHB metabolism in three types of bacteria, as follows: (A) In Ralstonia pickettii T1, an extracellular PHBDP degrades extracellular PHB to various-sized 3HB-oligomers, which an extracellular 3HBOH hydrolyzes to 3HB-monomers. (B) In Acidovorax sp. SA1, an extracellular PHBDP hydrolyzes extracellular PHB to small 3HB-oligomers (dimer and trimer), which an intracellular 3HBOH efficiently degrades to 3HB in the cell. (C) In Ralstonia eutropha H16, an intracellular 3HBOH helps in the degradation of intracellular PHB inclusions by PHBDP.
Title: Cloning of an intracellular D(-)-3-hydroxybutyrate-oligomer hydrolase gene from Ralstonia eutropha H16 and identification of the active site serine residue by site-directed mutagenesis Saegusa H, Shiraki M, Saito T Ref: J Biosci Bioeng, 94:106, 2002 : PubMed
An intracellular D(-)-3-hydroxybutyrate (3HB)-oligomer hydrolase gene from Ralstonia eutropha (formerly Alcaligenes eutrophus) H16 was cloned, sequenced, and characterized. As a hybridization probe to screen restriction digests of chromosomal DNA, an extracellular 3HB-oligomer hydrolase gene from Ralstonia pickettii strain (formerly Pseudomonas sp. strain) A1 was used. A specific hybridization signal was obtained and a 6.5-kbp SmaI fragment was cloned in an Escherichia coli phagemid vector. The crude extract from E. coli with this plasmid showed 3HB-trimer hydrolase activity. The subcloned 3.2-kbp fragment still showed 3HB-trimer hydrolase activity in E. coli and expressed an approximately 78-kDa protein in an in vitro transcription-translation system. Nucleotide sequence analysis of the 3.2-kbp fragment showed an open reading frame that encodes a polypeptide with a deduced molecular weight of 78,510. The putative amino acid sequence showed 54% identity with that of the oligomer hydrolase from R. pickettii A1. By site-directed mutagenesis, a novel amino acid sequence (S-V-S*-N-G) containing an essential serine residue in the catalytic center of the enzyme was determined. The gene product was found in PHB-rich cells of R. eutropha by immunodetection. The expressed 3HB-oligomer hydrolase localized both in the supernatant fraction and the PHB granules of the cells.
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Genes Proteins in OHBut_olig_hydro_put family (238)
Fragments of genes in OHBut_olig_hydro_put family (1)
