PMID:15489436

Citation	Handrick, R, Reinhardt, S, Kimmig, P and Jendrossek, D (2004) The "intracellular" poly(3-hydroxybutyrate) (PHB) depolymerase of Rhodospirillum rubrum is a periplasm-located protein with specificity for native PHB and with structural similarity to extracellular PHB depolymerases. J. Bacteriol. 186:7243-53
Abstract	Rhodospirillum rubrum possesses a putative intracellular poly(3-hydroxybutyrate) (PHB) depolymerase system consisting of a soluble PHB depolymerase, a heat-stable activator, and a 3-hydroxybutyrate dimer hydrolase (J. M. Merrick and M. Doudoroff, J. Bacteriol. 88:60-71, 1964). In this study we reinvestigated the soluble R. rubrum PHB depolymerase (PhaZ1). It turned out that PhaZ1 is a novel type of PHB depolymerase with unique properties. Purified PhaZ1 was specific for amorphous short-chain-length polyhydroxyalkanoates (PHA) such as native PHB, artificial PHB, and oligomer esters of (R)-3-hydroxybutyrate with 3 or more 3-hydroxybutyrate units. Atactic PHB, (S)-3-hydroxybutyrate oligomers, medium-chain-length PHA, and lipase substrates (triolein, tributyrin) were not hydrolyzed. The PHB depolymerase structural gene (phaZ1) was cloned. Its deduced amino acid sequence (37,704 Da) had no significant similarity to those of intracellular PHB depolymerases of Wautersia eutropha or of other PHB-accumulating bacteria. PhaZ1 was found to have strong amino acid homology with type-II catalytic domains of extracellular PHB depolymerases, and Ser(42), Asp(138), and His(178) were identified as catalytic-triad amino acids, with Ser(42) as the putative active site. Surprisingly, the first 23 amino acids of the PHB depolymerase previously assumed to be intracellular revealed features of classical signal peptides, and Edman sequencing of purified PhaZ1 confirmed the functionality of the predicted cleavage site. Extracellular PHB depolymerase activity was absent, and analysis of cell fractions unequivocally showed that PhaZ1 is a periplasm-located enzyme. The previously assumed intracellular activator/depolymerase system is unlikely to have a physiological function in PHB mobilization in vivo. A second gene, encoding the putative true intracellular PHB depolymerase (PhaZ2), was identified in the genome sequence of R. rubrum.
Links	PubMed PMC523223 Online version:10.1128/JB.186.21.7243-7253.2004
Keywords	Amino Acid Sequence; Carboxylic Ester Hydrolases/antagonists & inhibitors; Carboxylic Ester Hydrolases/chemistry; Carboxylic Ester Hydrolases/genetics; Carboxylic Ester Hydrolases/metabolism; Hydroxybutyrates/metabolism; Molecular Sequence Data; Periplasm/enzymology; Polyesters/metabolism; Rhodospirillum rubrum/enzymology; Rhodospirillum rubrum/genetics; Rhodospirillum rubrum/growth & development; Solubility; Substrate Specificity
edit table

Annotations

Gene product	Qualifier	GO Term	Evidence Code	with/from	Aspect	Extension	Notes	Status
RHORU:Q6YNP7		GO:0050526: poly(3-hydroxybutyrate) depolymerase activity	ECO:0000314:		F		Table 3 shows substrate specificity of PHB depolymerase PhaZ1	complete CACAO 3343
RHORU:Q6YNP7	enables	GO:0050526: poly(3-hydroxybutyrate) depolymerase activity	ECO:0000314: direct assay evidence used in manual assertion		F		Seeded From UniProt	complete

References

See Help:References for how to manage references in GONUTS.