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Publication Abstract from PubMed

Isopenicillin N synthase (IPNS) catalyses the synthesis of isopenicillin N (IPN), the biosynthetic precursor to penicillin and cephalosporin antibiotics. IPNS is a non-heme iron(II) oxidase that mediates the oxidative cyclisation of the tripeptide delta-L-alpha-aminoadipoyl-L-cysteinyl-D-valine (ACV) to IPN with a concomitant reduction of molecular oxygen to water. Solution-phase incubation experiments have shown that, although IPNS can turn over analogues with a diverse range of hydrocarbon side chains in the third (valinyl) position of its substrate, the enzyme is much less tolerant of polar residues in this position. Thus, although IPNS converts delta-L-alpha-aminoadipoyl-L-cysteinyl-D-isoleucine (ACI) and AC-D-allo-isoleucine (ACaI) to penam products, the isosteric sulfur-containing peptides AC-D-thiaisoleucine (ACtI) and AC-D-thia-allo-isoleucine (ACtaI) are not turned over. To determine why these peptides are not substrates, we crystallized ACtaI with IPNS. We report the synthesis of ACtaI and the crystal structure of the IPNS:Fe(II) :ACtaI complex to 1.79 A resolution. This structure reveals direct ligation of the thioether side chain to iron: the sulfide sulfur sits 2.66 A from the metal, squarely in the oxygen binding site. This result articulates a structural basis for the failure of IPNS to turn over these substrates.

Isopenicillin N Synthase Binds delta-(L-alpha-Aminoadipoyl)-L-Cysteinyl-D-Thia-allo-Isoleucine through both Sulfur Atoms.,Clifton IJ, Ge W, Adlington RM, Baldwin JE, Rutledge PJ Chembiochem. 2011 Aug 16;12(12):1881-5. doi: 10.1002/cbic.201100149. Epub, 2011 Jun 15. PMID:21678539^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.