Properties and substrate specificity of RppA, a chalcone synthase-related polyketide synthase in Streptomyces griseus.
RppA, a chalcone synthase-related polyketide synthase (type III polyketide synthase) in the bacterium Streptomyces griseus, catalyzes the formation of 1,3,6,8-tetrahydroxynaphthalene (THN) from five molecules of malonyl-CoA. The K(m) value for malonyl-CoA and the k(cat) value for THN synthesis were determined to be 0.93 +/- 0.1 microm and 0.77 +/- 0.04 min(-1), respectively. RppA accepted aliphatic acyl-CoAs with the carbon lengths from C(4) to C(8) as starter substrates and catalyzed sequential condensation of malonyl-CoA to yield alpha-pyrones and phloroglucinols. In addition, RppA yielded a hexaketide, 4-hydroxy-6-(2',4',6'-trioxotridecyl)-2-pyrone, from octanoyl-CoA and five molecules of malonyl-CoA, suggesting that the size of the active site cavity of RppA is larger than any other chalcone synthase-related enzymes found so far in plants and bacteria. RppA was also found to synthesize a C-methylated pyrone, 3,6-dimethyl-4-hydroxy-2-pyrone, by using acetoacetyl-CoA as the starter and methylmalonyl-CoA as an extender. Thus, the broad substrate specificity of RppA yields a wide variety of products.
Funa
Nobutaka
N
Department of Biotechnology, Graduate School of Agriculture and Life Sciences, University of Tokyo, Bunkyo-ku, Tokyo, Japan.
Ohnishi
Yasuo
Y
Ebizuka
Yutaka
Y
Horinouchi
Sueharu
S
D000217:Acyltransferases / Q000737:chemistry* / Q000378:metabolism*; D002851:Chromatography, High Pressure Liquid; D007202:Indicators and Reagents / Q000737:chemistry; D007700:Kinetics; D008956:Models, Chemical; D009097:Multienzyme Complexes / Q000737:chemistry*; D009284:Naphthols / Q000737:chemistry; D010696:Phloroglucinol / Q000737:chemistry; D013053:Spectrophotometry; D013305:Streptomyces griseus / Q000201:enzymology*; D013379:Substrate Specificity; D013997:Time Factors
C121288:1,3,6,8-tetrahydroxynaphthalene; D007202:Indicators and Reagents; D009097:Multienzyme Complexes; D009284:Naphthols; D010696:Phloroglucinol; D000217:Acyltransferases; C020141:flavanone synthetase