The unprocessed preprotein form IATC103S of the isopenicillin N acyltransferase is transported inside peroxisomes and regulates its self-processing

Previous studies in Penicillium chrysogenum and Aspergillus nidulans suggested that self-processing of the isopenicillin N acyltransferase (IAT) is an important differential factor in these fungi. Expression of a mutant penDEC103S gene in P. chrysogenum gave rise to an unprocessed inactive variant of IAT (IATC103S) located inside peroxisomes, which indicates that transport of the proIAT inside these organelles is not dependent on the processing state of the protein. Co-expression of the penDEC103S and wild-type penDE genes in P. chrysogenum (Wis54-DEC103S strain) led to a decrease in benzylpenicillin levels. Changes in the wild-type IAT processing profile (β subunit formation) were observed in the Wis54-DEC103S strain, suggesting a regulatory role of the unprocessed IATC103S in the processing of the wild-type IAT. This was confirmed in Escherichia coli, where a delay in the processing of IAT in presence of the unprocessable IATC103S was observed. Our results indicate that IAT is post-translationally regulated by its preprotein, which interferes with the self-processing.