title: Transacylase-like structure and its role in substrate channeling of 6-hydroxymellein synthase, a multifunctional polyketide biosynthetic enzyme in carrot cell extracts.
abstract: 6-Hydroxymellein synthase, a multifunctional polyketide biosynthetic enzyme of carrot, lost the binding ability toward its co-substrates, acetyl- and malonyl-CoAs, by the treatment with the blocking reagents for serine-OH. In contrast, the enzyme retained the binding ability even when the two SH groups at the reaction center (cysteine-SH of the condensation enzyme and cysteamine-SH of acyl carrier protein) were blocked, and one substrate bound to the SH-blocked enzyme was readily replaced by the other. It appeared that the cysteine-SH accepted only acetyl moiety while cysteamine-SH was preferentially malonylated in the presence of both of the substrates. These results suggest that transacylase-like domain is involved in the structure of 6-hydroxymellein synthase as a common primary binding site of its co-substrates, and acetyl and malonyl moieties are properly channeled from their CoA esters to cysteine-SH and acyl carrier protein-SH via this domain, respectively.
authors.affiliation: Cell Biology Laboratory, Faculty of Pharmaceutical Sciences, Toyama Medical and Pharmaceutical University, Japan.
authors.forename: F
authors.initials: F
authors.lastname: Kurosaki
mesh_terms: D000105:Acetyl Coenzyme A / Q000737:chemistry / Q000378:metabolism; D000213:Acyl Carrier Protein / Q000737:chemistry / Q000378:metabolism; D000217:Acyltransferases / Q000037:antagonists & inhibitors / Q000737:chemistry* / Q000378:metabolism*; D001665:Binding Sites; D003545:Cysteine / Q000737:chemistry / Q000378:metabolism; D018552:Daucus carota / Q000201:enzymology; D008025:Ligases / Q000037:antagonists & inhibitors / Q000737:chemistry* / Q000378:metabolism*; D008316:Malonyl Coenzyme A / Q000737:chemistry / Q000378:metabolism; D015394:Molecular Structure; D009097:Multienzyme Complexes / Q000037:antagonists & inhibitors / Q000737:chemistry* / Q000378:metabolism*; D010088:Oxidoreductases / Q000037:antagonists & inhibitors / Q000737:chemistry* / Q000378:metabolism*; D013379:Substrate Specificity; D013438:Sulfhydryl Compounds / Q000737:chemistry / Q000378:metabolism; D013439:Sulfhydryl Reagents / Q000494:pharmacology; D013450:Sulfones / Q000494:pharmacology
chemical_list: D000213:Acyl Carrier Protein; D009097:Multienzyme Complexes; D013438:Sulfhydryl Compounds; D013439:Sulfhydryl Reagents; D013450:Sulfones; C002010:4-(2-aminoethyl)benzenesulfonylfluoride; D008316:Malonyl Coenzyme A; D000105:Acetyl Coenzyme A; D010088:Oxidoreductases; D000217:Acyltransferases; C070623:6-hydroxymellein synthetase; D008025:Ligases; D003545:Cysteine