View source for 1axb

[[Image:1axb.gif|left|200px]]<br /><applet load="1axb" size="350" color="white" frame="true" align="right" spinBox="true" 
caption="1axb, resolution 2.0&Aring;" />
'''TEM-1 BETA-LACTAMASE FROM ESCHERICHIA COLI INHIBITED WITH AN ACYLATION TRANSITION STATE ANALOG'''<br />

==Overview==
The crystal structure of a phosphonate complex of the class A TEM-1 beta-lactamase has been determined to a resolution of 2.0 A. The phosphonate appears stoichiometrically at the active site, bound covalently to Ser70Ogamma, with one phosphonyl oxygen in the oxyanion hole. Although the overall structure is very similar to that of the native enzyme (rms difference 0.37 A for all heavy atoms), changes have occurred in the position of active site functional groups. The active site is also not in the conformation observed in the complex of another class A beta-lactamase, that of Staphylococcus aureus PC1, with the same phosphonate [Chen, C. C. H., et al. (1993) J. Mol. Biol. 234,165-178]. Both phosphonate structures, however, can be seen to represent models of acylation transition-states since in each the deacylating water molecule appears firmly bound to the Glu166 carboxylate group. The major difference between the structures lies in the positioning of Lys73Nzeta and Ser130Ogamma. In the S. aureus structure, the closest interaction of these functional groups is between Lys73Nzeta and Ser70Ogamma (2.8 A), while in the TEM-1 structure it is between Ser130Ogamma and the second phosphonyl oxygen of the bound inhibitor (2.8 A). The former structure therefore may resemble a transition state for formation of the tetrahedral species in acylation by nucleophilic attack on the substrate, where Lys73Nzeta presumably catalyzes the reaction as a general base. The TEM-1 structure can then be seen as an analogue of the transition state for breakdown of the tetrahedral species, where Ser130Ogamma is acting as a general acid, assisting the departure of the leaving group. The class A beta-lactamase crystal structures now available lead to a self-consistent proposal for a mechanism of catalysis by these enzymes.

==About this Structure==
1AXB is a [http://en.wikipedia.org/wiki/Single_protein Single protein] structure of sequence from [http://en.wikipedia.org/wiki/Escherichia_coli Escherichia coli] with <scene name='pdbligand=FOS:'>FOS</scene> as [http://en.wikipedia.org/wiki/ligand ligand]. Active as [http://en.wikipedia.org/wiki/Beta-lactamase Beta-lactamase], with EC number [http://www.brenda-enzymes.info/php/result_flat.php4?ecno=3.5.2.6 3.5.2.6] Full crystallographic information is available from [http://oca.weizmann.ac.il/oca-bin/ocashort?id=1AXB OCA]. 

==Reference==
Crystal structure of an acylation transition-state analog of the TEM-1 beta-lactamase. Mechanistic implications for class A beta-lactamases., Maveyraud L, Pratt RF, Samama JP, Biochemistry. 1998 Feb 24;37(8):2622-8. PMID:[http://ispc.weizmann.ac.il//pmbin/getpm?pmid=9485412 9485412]
[[Category: Beta-lactamase]]
[[Category: Escherichia coli]]
[[Category: Single protein]]
[[Category: Maveyraud, L.]]
[[Category: Pratt, R F.]]
[[Category: Samama, J P.]]
[[Category: FOS]]
[[Category: antibiotic resistance]]
[[Category: beta-lactamase]]
[[Category: hydrolase]]

''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Thu Feb 21 11:49:13 2008''