Alonso_1996_Microbiology_142_2951

The pip gene coding for the proline iminopeptidase (Pip) of Xanthomonas campestris pv. citri was cloned in an Escherichia coli leuB strain using a selective medium containing the dipeptide D-Ala-L-Leu as the sole source of L-leucine. Nucleotide sequencing of this gene revealed a 939 bp open reading frame encoding a 312 amino acid protein (35 126 Da). The deduced amino acid sequence showed 47% identity with the Pip from Neisseria gonorrhoeae. A lacZ-pip fusion gene was overexpressed in E. coli under the control of the Plac promoter. The Pip of X. campestris hydrolysed L-prolyl-p-nitroanilide with the highest efficiency, but was also able to hydrolyse L-alanyl-p-nitroanilide and D-alanyl-p-nitroanilide. The molecular mass of Pip was found to be 35 kDa by SDS-PAGE and 120 kDa by gel filtration, suggesting that the active enzyme is a multimer.