Bacterial ß-aminopeptidases: structural insights and applications for biocatalysis.

ABSTRACT

ß-Aminopeptidases comprise a class of enzymes with functional and structural similarities. All members of the ß-aminopeptidases described to date were isolated from bacterial sources. Uniquely, they catalyze the hydrolysis of ß(3) - and/or ß(2) -amino acid residues from amides and peptides that are otherwise considered proteolytically stable. Due to this unusual reactivity with ß-peptide substrates, ß-aminopeptidases have potential to be used as biocatalysts for ß-peptide synthesis and for the resolution of enantiomerically pure ß-amino acids from racemic substrate mixtures. ß-Aminopeptidases are formed from an inactive precursor by posttranslational autoproteolytic cleavage, exposing the catalytic nucleophile at the N-terminus of the newly formed ß-polypeptide chain. Such an activation step is a characteristic trait of enzymes of the N-terminal nucleophile (Ntn) hydrolase superfamily. However, classical Ntn hydrolases and ß-aminopeptidases differ by the fold of their catalytic cores and are hence likely to originate from distinct evolutionary ancestors. In this contribution, we review the existing literature on ß-aminopeptidases, including biochemical and functional studies, as well as structural investigations that recently allowed insights into the catalytic mechanisms of precursor processing and ß-peptide conversion.