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[摘要]：OxyB catalyzes the first oxidative phenol coupling reaction in vancomycin biosynthesis. OxyB is a P450 hemoprotein whose activity is strictly dependent upon the presence of molecular oxygen. Here, it was shown that label from O-18(2) is not incorporated into the monocyclic product during catalysis by OxyB. In addition, it was shown that OxyB can convert a model hexapeptide substrate containing (R)-Tyr6, instead of (S)-Tyr6, covalently linked as a C-terminal thioester to a peptidyl carrier protein (PCP-7S) derived from the vancomycin non-ribosomal peptide synthetase (NRPS), into the corresponding epimeric monocyclic product. The binding of this epimeric hexapeptide-PCP conjugate to the Fe(III) form of OxyB, as monitored by UV-vis spectroscopy, revealed a K-d = 35 +/- 5 mu M. Thus, the enzyme reveals a surprising lack of stereospecificity in the binding and transformation of these epimeric substrates. (c) 2007 Elsevier Ltd. All rights reserved. |
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