This is the N-terminal domain of Streptomyces clavuligerus ORF 12 gene product, which is directly involved in biosynthesis of Clavulanic acid (CA). The N-terminal domain consists of one four-stranded antiparallel beta-sheet surrounded by four alpha-helices and folds similarly to steroid isomerases and polyketide cyclases (PKTC). However, the N-terminal domain has no apparent polar-lined active-site pocket or conserved catalytic residues analogous to those of either the steroid isomerases or PKTCs. ORF 12 has 2 binding sites, CA is able to bind both to an active site and between the two domains. The active site pocket is lined by residues from both the N- and the C-terminal domains (His88, Ser173, Thr209, Ser234, Ser278, Met383, Phe374, Ala376 and Phe385). The C-2 carboxylate of CA is positioned deep in the pocket, making electrostatic interactions with Lys375, Arg418 and Lys89. Lys89 is located in strand beta-2 of the N-terminal domain and may also be involved in the beta-lactam core-binding region, including the residues Lys89 as well as Arg418 [1].

1: Structural and mechanistic studies of the orf12 gene product from the clavulanic acid biosynthesis pathway. Valegard K, Iqbal A, Kershaw NJ, Ivison D, Genereux C, Dubus A, Blikstad C, Demetriades M, Hopkinson RJ, Lloyd AJ, Roper DI, Schofield CJ, Andersson I, McDonough MA; Acta Crystallogr D Biol Crystallogr. 2013;69:1567-1579. PMID:23897479