期刊
CHEMISTRY-A EUROPEAN JOURNAL
卷 23, 期 52, 页码 12815-12824出版社
WILEY-V C H VERLAG GMBH
DOI: 10.1002/chem.201701592
关键词
biosynthesis; enzymes; metalloenzymes; non-heme oxygenase; oxidoreductases; penicillin
资金
- BBSRC
- EPSRC
- Wellcome Trust
- Deutscher Akademischer Austauschdienst
Isopenicillin N synthase (IPNS) catalyses the four-electron oxidation of a tripeptide, L-delta(-aminoadipoyl)-l-cysteinyl-d-valine (ACV), to give isopenicillin N (IPN), the first-formed beta-lactam in penicillin and cephalosporin biosynthesis. IPNS catalysis is dependent upon an iron(II) cofactor and oxygen as a co-substrate. In the absence of substrate, the carbonyl oxygen of the side-chain amide of the penultimate residue, Gln330, co-ordinates to the active-site metal iron. Substrate binding ablates the interaction between Gln330 and the metal, triggering rearrangement of seven C-terminal residues, which move to take up a conformation that extends the final alpha-helix and encloses ACV in the active site. Mutagenesis studies are reported, which probe the role of the C-terminal and other aspects of the substrate binding pocket in IPNS. The hydrophobic nature of amino acid side-chains around the ACV binding pocket is important in catalysis. Deletion of seven C-terminal residues exposes the active site and leads to formation of a new type of thiol oxidation product. The isolated product is shown by LC-MS and NMR analyses to be the ene-thiol tautomer of a dithioester, made up from two molecules of ACV linked between the thiol sulfur of one tripeptide and the oxidised cysteinyl beta-carbon of the other. A mechanism for its formation is proposed, supported by an X-ray crystal structure, which shows the substrate ACV bound at the active site, its cysteinyl beta-carbon exposed to attack by a second molecule of substrate, adjacent. Formation of this product constitutes a new mode of reaction for IPNS and non-heme iron oxidases in general.
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