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.