Conserved structural modules and bonding networks in isopenicillin N synthase related non-haem iron-dependent oxygenases and oxidases

Analyses of attainable primary amino acid sequences, assigned secondary structures and superimposed tertiary structures of 142 isopenicillin N synthase (IPNS) related non-haem iron-dependent oxygenases and oxidases (designated as NHIDOX) were examined in this study. Despite having low sequence homologies (∼20%), these enzymes were found to possess conserved structural domains (delineated as modules I and II) that fold into jelly-roll motifs, juxtaposed by adjacent stabilizing elements. The seven highly conserved residues, corresponding to His214, Asp216 and His270 in Aspergillus nidulans IPNS (IPNS_AN) for iron binding, Arg279 and Ser281 for substrate/co-substrate binding, as well as Gly40 and Gly254 with yet undetermined functions, are arrayed closely within these conserved modules. Complex hydrogen bonding interactions of these conserved residues with residues found in specific α-helices and β-strands of the conserved core motif are apparently involved in stabilizing these structures. Although the NHIDOX enzymes appear to share conserved active center architecture, differences in their hydrogen bonding networks were observed, particularly those involving the substrate/co-substrate binding ligands and the two conserved glycines. These may modulate functional versatilities, relative sizes of the jelly-roll motifs, and the specific amino acid residues involved in stabilization and folding of the active center.