1ong
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(New page: 200px<br /><applet load="1ong" size="450" color="white" frame="true" align="right" spinBox="true" caption="1ong, resolution 1.10Å" /> '''SHV-1 beta-lactamase...)
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Revision as of 20:55, 20 November 2007
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SHV-1 beta-lactamase with a penem inhibitor
Overview
A new beta-lactamase inhibitor, a methylidene penem having a, 5,6-dihydro-8H-imidazo[2,1-c][1,4]oxazine heterocyclic substituent at the, C6 position with a Z configuration, irreversibly inhibits both class A and, class C serine beta-lactamases with IC(50) values of 0.4 and 9.0 nM for, TEM-1 and SHV-1 (class A), respectively, and 4.8 nM in AmpC (class C), beta-lactamases. The compound also inhibits irreversibly the class C, extended-spectrum GC1 beta-lactamase (IC(50) = 6.2 nM). High-resolution, crystallographic structures of a reaction intermediate of, (5R)-(6Z)-6-(5,6-dihydro-8H-imidazo[2,1-c][1,4]oxazin-2-ylmethylene)-7-oxo, -4-thia-1-azabicyclo[3.2.0]hept-2-ene-3-carboxylic acid 1 with the SHV-1, beta-lactamase and with the GC1 beta-lactamase have been determined by, X-ray diffraction to resolutions of 1.10 and 1.38 A, respectively. The two, complexes were refined to crystallographic R-factors (R(free)) of 0.141, (0.186) and 0.138 (0.202), respectively. Cryoquenching of the reaction of, 1 with each beta-lactamase crystal produced a common, covalently bound, intermediate. After acylation of the serine, a nucleophilic attack by the, departing thiolate on the C6' atom yielded a novel seven-membered, 1,4-thiazepine ring having R stereochemistry at the new C7 moiety. The, orientation of this ring in each complex differs by a 180 degrees rotation, about the bond to the acylated serine. The acyl ester bond is stabilized, to hydrolysis through resonance stabilization with the dihydrothiazepine, ring and by low occupancy or disorder of hydrolytic water molecules. In, the class A complex, the buried water molecule on the alpha-face of the, ester bond appears to be loosely bound or absent. In the class C complex, a water molecule on the beta-face is disordered and poorly activated for, hydrolysis. Here, the acyl intermediate is unable to assist its own, hydrolysis, as is thought to occur with many class C substrates.
About this Structure
1ONG is a Single protein structure of sequence from Klebsiella pneumoniae with MA4 and WY4 as ligands. Active as Beta-lactamase, with EC number 3.5.2.6 Full crystallographic information is available from OCA.
Reference
Inhibition of class A and class C beta-lactamases by penems: crystallographic structures of a novel 1,4-thiazepine intermediate., Nukaga M, Abe T, Venkatesan AM, Mansour TS, Bonomo RA, Knox JR, Biochemistry. 2003 Nov 18;42(45):13152-9. PMID:14609325
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