Unique binding of a non-natural l,l,l-substrate by isopenicillin N synthase

Isopenicillin N synthase (IPNS) is a non-haem iron oxidase that catalyses the formation of isopenicillin N from the tripeptide δ-(l-α-aminoadipoyl)-l-cysteinyl-d-valine. In this report, we describe the crystal structure of the enzyme with a non-natural l,l,l-tripeptide substrate, δ-(l-α-aminoadipoyl)-l-cysteinyl-l-3,3,3,3′,3′,3′-hexafluorovaline. This structure reveals a strong binding interaction of the tripeptide within the active site and a unique conformation for the non-natural l,l,l-diastereomer. Taken together, these findings provide a possible rationale for the previously observed inhibitory effects of l,l,l-tripeptide substrates on IPNS activity.