Enzymatic Degradation of β‐ and Mixed α,β‐Oligopeptides

One of the main and most astonishing characteristics of peptides comprised of β‐amino acids with proteinogenic side chains is their extraordinarily high stability towards enzymatic degradation. So far, only certain microbial enzymes have been shown to cleave N‐terminal β3‐homoamino acid residues from peptides. In this work, the L‐aminopeptidase‐D‐amidase/esterase (DmpA) from Ochrobactrum anthropi LMG7991 is compared to two closely related β‐peptidyl aminopeptidases (BapA), which originate from Sphingosinicella strains, and to microsomal leucine aminopeptidase (LAP) as a reference. All four enzymes are aminopeptidases cleaving N‐terminal amino acids from small peptides. Degradation experiments reveal that DmpA and both BapA enzymes exhibit unique, but clearly distinct substrate specificities and preferences. DmpA also cleaves β‐ and mixed α,β‐peptides and amides, but a short side chain of the N‐terminal β‐amino acid residue seems to be a prerequisite, since only peptides carrying N‐terminal βhGly and β3hAla are hydrolyzed with good efficiencies. Both β‐peptidyl aminopeptidases cleave β‐amino acids from a variety of β‐peptides and mixed α,β‐peptides, but they do not accept α‐amino acids in the N‐terminal position. Astonishingly, DmpA exhibited much higher catalytical rates for the mixed dipeptide carnosine (H‐βhGly‐His‐OH) than for any other substrate described until now.