1n9b
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Ultrahigh resolution structure of a class A beta-lactamase: On the mechanism and specificity of the extended-spectrum SHV-2 enzyme
OverviewOverview
Bacterial beta-lactamases hydrolyze beta-lactam antibiotics such as, penicillins and cephalosporins. The TEM-type class A beta-lactamase SHV-2, is a natural variant that exhibits activity against third-generation, cephalosporins normally resistant to hydrolysis by class A enzymes. SHV-2, contains a single Gly238Ser change relative to the wild-type enzyme SHV-1., Crystallographic refinement of a model including hydrogen atoms gave R and, R(free) of 12.4% and 15.0% for data to 0.91 A resolution. The hydrogen, atom on the O(gamma) atom of the reactive Ser70 is clearly seen for the, first time, bridging to the water molecule activated by Glu166. Though, hydrogen atoms on the nearby Lys73 are not seen, this observation of the, Ser70 hydrogen atom and the hydrogen bonding pattern around Lys73 indicate, that Lys73 is protonated. These findings support a role for the, Glu166-water couple, rather than Lys73, as the general base in the, deprotonation of Ser70 in the acylation process of class A, beta-lactamases. Overlay of SHV-2 with SHV-1 shows a significant 1-3 A, displacement in the 238-242 beta-strand-turn segment, making the, beta-lactam binding site more open to newer cephalosporins with large C7, substituents and thereby expanding the substrate spectrum of the variant, enzyme. The OH group of the buried Ser238 side-chain hydrogen bonds to the, main-chain CO of Asn170 on the Omega loop, that is unaltered in position, relative to SHV-1. This structural role for Ser238 in protein-protein, binding makes less likely its hydrogen bonding to oximino cephalosporins, such as cefotaxime or ceftazidime.
About this StructureAbout this Structure
1N9B is a Single protein structure of sequence from Klebsiella pneumoniae with MA4, EPE and MPD as ligands. Active as Beta-lactamase, with EC number 3.5.2.6 Full crystallographic information is available from OCA.
ReferenceReference
Ultrahigh resolution structure of a class A beta-lactamase: on the mechanism and specificity of the extended-spectrum SHV-2 enzyme., Nukaga M, Mayama K, Hujer AM, Bonomo RA, Knox JR, J Mol Biol. 2003 Apr 18;328(1):289-301. PMID:12684014
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