1es4
|
C98N mutant of streptomyces K15 DD-transpeptidase
OverviewOverview
The Streptomyces K15 penicillin-binding DD-transpeptidase is presumed to, be involved in peptide cross-linking during bacterial cell wall, peptidoglycan assembly. To gain insight into the catalytic mechanism, the, roles of residues Lys38, Ser96, and Cys98, belonging to the structural, elements defining the active site cleft, have been investigated by, site-directed mutagenesis, biochemical studies, and X-ray diffraction, analysis. The Lys38His and Ser96Ala mutations almost completely abolished, the penicillin binding and severely impaired the transpeptidase activities, while the geometry of the active site was essentially the same as in the, wild-type enzyme. It is proposed that Lys38 acts as the catalytic base, that abstracts a proton from the active serine Ser35 during nucleophilic, attack and that Ser96 is a key intermediate in the proton transfer from, the Ogamma of Ser35 to the substrate leaving group nitrogen. The role of, these two residues should be conserved among penicillin-binding proteins, containing the Ser-Xaa-Asn/Cys sequence in motif 2. Conversion of Cys98, into Asn decreased the transpeptidase activity and increased hydrolysis of, the thiolester substrate and the acylation rate with most beta-lactam, antibiotics. Cys98 is proposed to play the same role as Asn in motif 2 of, other penicilloyl serine transferases in properly positioning the, substrate for the catalytic process.
About this StructureAbout this Structure
1ES4 is a Single protein structure of sequence from Streptomyces sp.. Active as Serine-type D-Ala-D-Ala carboxypeptidase, with EC number 3.4.16.4 Full crystallographic information is available from OCA.
ReferenceReference
Catalytic mechanism of the Streptomyces K15 DD-transpeptidase/penicillin-binding protein probed by site-directed mutagenesis and structural analysis., Rhazi N, Charlier P, Dehareng D, Engher D, Vermeire M, Frere JM, Nguyen-Disteche M, Fonze E, Biochemistry. 2003 Mar 18;42(10):2895-906. PMID:12627955
Page seeded by OCA on Tue Nov 20 14:15:55 2007