Production of a fully functional, permuted single-chain penicillin G acylase

Penicillin G acylase (PGA) is a heterodimeric enzyme synthesized as a single-polypeptide precursor that undergoes an autocatalytic processing to remove an internal spacer peptide to produce the active enzyme. We constructed a single-chain PGA not dependent on autoproteolytic processing. The mature sequence of the beta-domain was expressed as the N terminus of a new polypeptide, connected by a random tetra-peptide to the alpha-domain, to afford a permuted protein. We found several active enzymes among variants differing in their linker peptides. Protein expression analysis showed that the functional single-chain variants were produced when using a Sec-dependent leader peptide, or when expressed inside the bacterial cytoplasm. Active-site titration experiments showed that the single-chain proteins displayed similar k(cat) values to the ones obtained with the wild-type enzyme. Interestingly, the single-chain proteins also displayed close to 100% of functional active sites compared to 40% to 70% functional yield usually obtained with the heterodimeric protein.