During the biosynthesis of most ansamycin antibiotics such as rifamycins, streptovaricins, naphthomycins, and chaxamycins, the activity is catalysed by the loading domain of the respective polyketide synthase (PKS), which transfers the substrate to the acyl-carrier protein domain of the first extension module of the PKS. During the biosynthesis of the mitomycins the reaction is catalysed by the MitE protein, which transfers the substrate to a dedicated acyl-carrier protein (MmcB).
The enzyme appears in viruses and cellular organisms
During the biosynthesis of most ansamycin antibiotics such as rifamycins, streptovaricins, naphthomycins, and chaxamycins, the activity is catalysed by the loading domain of the respective polyketide synthase (PKS), which transfers the substrate to the acyl-carrier protein domain of the first extension module of the PKS. During the biosynthesis of the mitomycins the reaction is catalysed by the MitE protein, which transfers the substrate to a dedicated acyl-carrier protein (MmcB).
Substrates: less than 5% of the activity with 3-amino-5-hydroxybenzoate: 3,5-dihydroxybenzoate, 3-chlorobenzoate, 3-bromobenzoate, benzoate Products: -
the loading module (LM) of Rif synthetase activates 3-amino-5-hydroxybenzoate (AHB) as AHB-AMP and links it to the phosphopantetheine arm of its thiolation domain (T1). AHB is then transferred across the non-ribosomal peptide synthase interface to the active-site cysteine of the ketosynthase domain of PKS module 1 (M1), and this second intermediate reacts with a methylmalonyl moiety to form an aryl ketide covalently bound to the M1 thiolation domain (T2). Occupancy of the T2 domain of LM-M1 by a methylmalonyl moiety triggers intermodular transfer of benzoate from the T1 domain to the KS domain, and this transthiolation event is fast relative to the initial loading of benzoate onto the T1 domain
rifamycin synthetase is primed with a 3-amino-5-hydroxybenzoate starter unit by a loading module that contains domains homologous to the adenylation and thiolation domains of nonribosomal peptide synthetases. The thiolation domain requires covalent attachment of the 4'-phosphopantetheine moiety of CoA to a conserved serine to be active. The catalytic models for the mechanism of the adenylation and thiolation didomain involve activation of 3-amino-5-hydroxybenzoate as the aryl-adenylate by the adenylation domain, followed by eventual formation of a covalent aryl thioester enzyme intermediate from attack of either aryl-CoA or the aryl-adenylate by the thiol nucleophile of the phosphopantetheine cofactor of the thiolation domain
during biosynthesis of mitomycin C, MitE catalyzes the reaction between aminohydroxybenzoate-AMP and MmcB to provide an aminohydroxybenzoate-ACP conjugate
preparation of several potential substrates believed to be early biosynthetic intermediates to FR900482 and the mitomycins to reveal the biochemical production of mitomycin C and FR900482
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