The mechanism for isopenicillin N synthase from density-functional modeling highlights the similarities with other enzymes in the 2-his-1-carboxylate family
2008 (English)In: Biochemistry, ISSN 0006-2960, E-ISSN 1520-4995, Vol. 47, no 3, 1031-1042 p.Article in journal (Refereed) Published
Isopenicillin N synthase (IPNS) catalyzes a key step in the biosynthesis of the important P-lactam antibiotics penicillins and cephalosporins. Density-functional calculations with the B3LYP functional are used to propose a detailed mechanism for this reaction. The results support the general scheme outlined from experimental observations, with formation of a four-membered beta-lactam ring followed by formation of a five-membered thiazolidine ring. However, an alternative mechanism for the heterolytic O-O bond cleavage and beta-lactam ring formation steps is proposed. The former part involves protonation of the distal oxygen by an iron-bound water ligand. This mechanism highlights the strong similarities that exist between IPNS and other enzymes of the 2-histidine-1-carboxylate family, especially pterin-dependent amino acid hydroxylases and alpha-keto acid-dependent dioxygenases. Both activation of the cysteine beta-C-H bond by an iron-bound superoxo radical and activation of the valine beta-C-H bond by a ferryl-oxo species show reaction barriers close to the experimentally measured one. These results are in agreement with kinetic isotope experiments that suggest both C-H bond activation steps to be partially rate limiting. The ring formation sequence is determined by the relative strengths of the two C-H bonds. Only the ferryl-oxo intermediate is capable of activating the stronger valine beta-C-H bond.
Place, publisher, year, edition, pages
2008. Vol. 47, no 3, 1031-1042 p.
IdentifiersURN: urn:nbn:se:uu:diva-145473DOI: 10.1021/bi701577qPubMedID: 18163649OAI: oai:DiVA.org:uu-145473DiVA: diva2:396502