title: Beta-lactamase of Bacillus licheniformis 749/C at 2 A resolution.
abstract: Two crystal forms (A and B) of the 29,500 Da Class A beta-lactamase (penicillinase) from Bacillus licheniformis 749/C have been examined crystallographically. The structure of B-form crystals has been solved to 2 A resolution, the starting model for which was a 3.5 A structure obtained from A-form crystals. The beta-lactamase has an alpha + beta structure with 11 helices and 5 beta-strands seen also in a penicillin target DD-peptidase of Streptomyces R61. Atomic parameters of the two molecules in the asymmetric unit were refined by simulated annealing at 2.0 A resolution. The R factor is 0.208 for the 27,330 data greater than 3 sigma (F), with water molecules excluded from the model. The catalytic Ser-70 is at the N-terminus of a helix and is within hydrogen bonding distance of conserved Lys-73. Also interacting with the Lys-73 are Asn-132 and the conserved Glu-166, which is on a potentially flexible helix-containing loop. The structure suggests the binding of beta-lactam substrates is facilitated by interactions with Lys-234, Thr-235, and Ala-237 in a conserved beta-strand peptide, which is antiparallel to the beta-lactam's acylamido linkage; an exposed cavity near Asn-170 exists for acylamido substituents. The reactive double bond of clavulanate-type inhibitors may interact with Arg-244 on the fourth beta-strand. A very similar binding site architecture is seen in the DD-peptidase.
authors.affiliation: Department of Molecular and Cell Biology, University of Connecticut, Storrs 06269.
authors.forename: P C
authors.initials: PC
authors.lastname: Moews
authors.forename: J R
authors.initials: JR
authors.lastname: Knox
authors.forename: O
authors.initials: O
authors.lastname: Dideberg
authors.forename: P
authors.initials: P
authors.lastname: Charlier
authors.forename: J M
authors.initials: JM
authors.lastname: Frère
mesh_terms: D001407:Bacillus / Q000201:enzymology* / Q000235:genetics; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D001665:Binding Sites; D008958:Models, Molecular; D010405:Penicillinase / Q000235:genetics / Q000378:metabolism; D010406:Penicillins / Q000378:metabolism; D011485:Protein Binding; D011487:Protein Conformation; D014961:X-Ray Diffraction
chemical_list: D001426:Bacterial Proteins; D010406:Penicillins; D010405:Penicillinase