Simultaneous accumulation and degradation of polyhydroxyalkanoates: futile cycle or clever regulation?
The regulation of medium-chain-length polyhydroxyalkanoates (mcl-PHA) metabolism in Pseudomonas putida GPo1 was studied by analysis of enzymes bound to PHA granules and enzymes involved in fatty acid oxidation. N-terminal sequencing of granule-bound enzymes revealed the presence of PHA polymerase (PhaC) and PHA depolymerase (PhaZ) and an acyl-CoA synthetase (ACS1), which recently was found to be associated with PHA granules by in vivo study. The acs1 knockout mutant accumulated 30-50% less PHA than its parental strain, confirming the involvement of ACS1 in PHA metabolism. Isolated PHA granules showed both PhaC and PhaZ activities. PhaC activity was found to be sensitive to the ratio of [R-3-hydroxyacyl-CoA]/[CoA] in which free CoA was a mild competitive inhibitor. Fatty acid oxidation was regulated by the [acetyl-CoA]/[CoA] and [NADH]/[NAD] ratios, with high ratios resulting in accumulation and low ratios leading to rapid oxidation of 3-hydroxyacyl-CoA. These results suggest that PHA metabolism is likely to be controlled by the [acetyl-CoA]/[CoA] and [NADH]/[NAD] ratios. The physiological roles of simultaneous PHA accumulation and degradation are also discussed.
Ren
Qun
Q
Laboratory of Biomaterials, Swiss Federal Laboratories for Materials Testing and Research (Empa), CH-9014 St. Gallen, Switzerland. qun.ren@empa.ch
de Roo
Guy
G
Ruth
Katinka
K
Witholt
Bernard
B
Zinn
Manfred
M
Thöny-Meyer
Linda
L
D000105:Acetyl Coenzyme A / Q000378:metabolism; D000217:Acyltransferases / Q000378:metabolism*; D001426:Bacterial Proteins / Q000378:metabolism*; D002210:Caprylates / Q000378:metabolism; D002265:Carboxylic Ester Hydrolases / Q000378:metabolism*; D002849:Chromatography, Gas; D003066:Coenzyme A Ligases / Q000502:physiology*; D003594:Cytoplasmic Granules; D005227:Fatty Acids / Q000737:chemistry / Q000378:metabolism*; D017353:Gene Deletion; D015971:Gene Expression Regulation, Enzymologic; D055786:Gene Knockout Techniques; D013058:Mass Spectrometry; D009154:Mutation / Q000235:genetics; D009243:NAD / Q000378:metabolism; D010084:Oxidation-Reduction; D054813:Polyhydroxyalkanoates / Q000378:metabolism*; D011401:Promoter Regions, Genetic / Q000235:genetics; D016958:Pseudomonas putida / Q000201:enzymology; D015219:Substrate Cycling
D001426:Bacterial Proteins; D002210:Caprylates; D005227:Fatty Acids; D054813:Polyhydroxyalkanoates; D009243:NAD; D000105:Acetyl Coenzyme A; C101940:3-hydroxyoctanoic acid; D000217:Acyltransferases; C067032:poly(3-hydroxyalkenoate)polymerase; D002265:Carboxylic Ester Hydrolases; C077226:poly(3-hydroxyalkanoic acid) depolymerase; D003066:Coenzyme A Ligases; C561832:Acsl1 protein, rat