title: Substrate specificity of a peptidyl-aminoacyl-L/D-isomerase from frog skin.
abstract: In the skin of fire-bellied toads (Bombina species), an aminoacyl-L/D-isomerase activity is present which catalyses the post-translational isomerization of the L- to the D-form of the second residue of its substrate peptides. Previously, this new type of enzyme was studied in some detail and genes potentially coding for similar polypeptides were found to exist in several vertebrate species including man. Here, we present our studies to the substrate specificity of this isomerase using fluorescence-labeled variants of the natural substrate bombinin H with different amino acids at positions 1, 2 or 3. Surprisingly, this enzyme has a rather low selectivity for residues at position 2 where the change of chirality at the alpha-carbon takes place. In contrast, a hydrophobic amino acid at position 1 and a small one at position 3 of the substrate are essential. Interestingly, some peptides containing a Phe at position 3 also were substrates. Furthermore, we investigated the role of the amino-terminus for substrate recognition. In view of the rather broad specificity of the frog isomerase, we made a databank search for potential substrates of such an enzyme. Indeed, numerous peptides of amphibia and mammals were found which fulfill the requirements determined in this study. Expression of isomerases with similar characteristics in other species can therefore be expected to catalyze the formation of peptides containing D-amino acids.
authors.affiliation: Institute of Organic Chemistry, Johannes Kepler University Linz, Altenberger Str. 69, 4040, Linz, Austria. alex.jilek@gmx.at
authors.forename: Alexander
authors.initials: A
authors.lastname: Jilek
authors.forename: Christa
authors.initials: C
authors.lastname: Mollay
authors.forename: Karl
authors.initials: K
authors.lastname: Lohner
authors.forename: Günther
authors.initials: G
authors.lastname: Kreil
mesh_terms: D000591:Amino Acid Isomerases / Q000737:chemistry* / Q000302:isolation & purification; D019943:Amino Acid Substitution; D000596:Amino Acids / Q000737:chemistry*; D000818:Animals; D023181:Antimicrobial Cationic Peptides / Q000737:chemistry; D001001:Anura; D008297:Male; D010455:Peptides / Q000737:chemistry* / Q000378:metabolism; D011499:Protein Processing, Post-Translational; D012867:Skin / Q000737:chemistry / Q000201:enzymology*; D013237:Stereoisomerism; D013379:Substrate Specificity
chemical_list: D000596:Amino Acids; D023181:Antimicrobial Cationic Peptides; D010455:Peptides; C510197:bombinin H2; D000591:Amino Acid Isomerases