title: Crystal structures of BapA complexes with β-lactam-derived inhibitors illustrate substrate specificity and enantioselectivity of β-aminopeptidases.
abstract: β-Aminopeptidases have exclusive biocatalytic potential because they react with peptides composed of β-amino acids, which serve as building blocks for the design of non-natural peptidomimetics. We have identified the β-lactam antibiotic ampicillin and the ampicillin-derived penicilloic acid as novel inhibitors of the β-aminopeptidase BapA from Sphingosinicella xenopeptidilytica (K(i)  values of 0.69 and 0.74 mM, respectively). We report high-resolution crystal structures of BapA in noncovalent complexes with these inhibitors and with the serine protease inhibitor 4-(2-aminoethyl)benzenesulfonyl fluoride. All three inhibitors showed similar binding characteristics; the aromatic moiety extended into a hydrophobic binding pocket of the active site, and the free amino group formed a salt bridge with Glu133 of BapA. The exact position of the inhibitors and structural details of the ligand binding pocket illustrate the specificity and the enantioselectivity of BapA-catalyzed reactions with β-peptide substrates.
authors.affiliation: Eawag, Swiss Federal Institute of Aquatic Science and Technology, Department of Environmental Microbiology, Überlandstrasse 133, 8600 Dübendorf, Switzerland.
authors.forename: Tobias
authors.initials: T
authors.lastname: Heck
authors.forename: Tobias
authors.initials: T
authors.lastname: Merz
authors.forename: Artur
authors.initials: A
authors.lastname: Reimer
authors.forename: Dieter
authors.initials: D
authors.lastname: Seebach
authors.forename: Daniel
authors.initials: D
authors.lastname: Rentsch
authors.forename: Christophe
authors.initials: C
authors.lastname: Briand
authors.forename: Markus G
authors.initials: MG
authors.lastname: Grütter
authors.forename: Hans-Peter E
authors.initials: HP
authors.lastname: Kohler
authors.forename: Birgit
authors.initials: B
authors.lastname: Geueke
mesh_terms: D000626:Aminopeptidases / Q000737:chemistry / Q000378:metabolism*; D000900:Anti-Bacterial Agents / Q000737:chemistry; D001426:Bacterial Proteins / Q000737:chemistry / Q000378:metabolism*; D001665:Binding Sites; D055162:Biocatalysis; D018360:Crystallography, X-Ray; D017434:Protein Structure, Tertiary; D015842:Serine Proteinase Inhibitors / Q000737:chemistry*; D042301:Sphingomonadaceae / Q000201:enzymology; D013237:Stereoisomerism; D013379:Substrate Specificity; D013450:Sulfones / Q000737:chemistry; D047090:beta-Lactams / Q000737:chemistry*
chemical_list: D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D015842:Serine Proteinase Inhibitors; D013450:Sulfones; D047090:beta-Lactams; C002010:4-(2-aminoethyl)benzenesulfonylfluoride; D000626:Aminopeptidases