Analysis of a conserved arginine R281L in catalysis in Cephalosporium acremonium isopenicillin N synthase

Abstract

Isopenicillin N synthase is essential for the catalytic transformation of a linear tripeptide substrate δ-(L-α-aminoadipyl)-Lcysteinyl-D-valine to isopenicillin N in the biosynthesis of β-lactam antibiotics. The recent Aspergillus nidulans isopenicillin N synthase crystal structure proposed that a conserved arginine, R279, has a role in substrate binding. This study, the first site-directed mutagenesis experiment on arginine in isopenicillin N synthase, was carried out to ascertain the role of the similarly conserved and corresponding arginine residue R281 on catalysis in the fungal Cephalosporium acremonium isopenicillin N synthase. Replacement of the arginine residue with leucine to generate the mutant R281L Cephalosporium isopenicillin N synthase resulted in undetectable activity as shown by enzyme bioassays. It is possible that the mutant's substrate binding capability was eliminated, thus preventing the catalytic reaction. Further investigation into the corresponding arginine residues in isopenicillin N synthase of other species is warranted.