2xlb

ACETYL XYLAN ESTERASE FROM BACILLUS PUMILUS WITHOUT LIGANDS

spinqualitylabelsall models 2xlb, resolution 1.90Å Show:Asymmetric Unit Biological Assembly Drag the structure with the mouse to rotate   Export Animated Image   Print3D Structural highlights 2xlb is a 12 chain structure with sequence from Bacillus pumilus. Full crystallographic information is available from OCA. For a guided tour on the structure components use FirstGlance. Related: 2xlc Activity: Acetylxylan esterase, with EC number 3.1.1.72 Resources: FirstGlance, OCA, RCSB, PDBsum Publication Abstract from PubMed Organophosphorus insecticides and nerve agents irreversibly inhibit serine hydrolase superfamily enzymes. One enzyme of this superfamily, the industrially important (for beta-lactam antibiotic synthesis) AXE/CAH (acetyl xylan esterase/cephalosporin acetyl hydrolase) from the biotechnologically valuable organism Bacillus pumilus, exhibits low sensitivity to the organophosphate paraoxon (diethyl-p-nitrophenyl phosphate, also called paraoxon-ethyl), reflected in a high Ki for it (~5 mM) and in a slow formation (t(1/2)~1 min) of the covalent adduct of the enzyme and for DEP (E-DEP, enzyme-diethyl phosphate, i.e. enzyme-paraoxon). The crystal structure of the E-DEP complex determined at 2.7 A resolution (1 A=0.1 nm) reveals strain in the active Ser181-bound organophosphate as a likely cause for the limited paraoxon sensitivity. The strain results from active-site-size limitation imposed by bulky conserved aromatic residues that may exclude as substrates esters having acyl groups larger than acetate. Interestingly, in the doughnut-like homohexamer of the enzyme, the six active sites are confined within a central chamber formed between two 60 degrees -staggered trimers. The exclusive access to this chamber through a hole around the three-fold axis possibly limits the size of the xylan natural substrates. The enzyme provides a rigid scaffold for catalysis, as reflected in the lack of movement associated with paraoxon adduct formation, as revealed by comparing this adduct structure with that also determined in the present study at 1.9 A resolution for the paraoxon-free enzyme. The crystal structure of the cephalosporin deacetylating enzyme acetyl xylan esterase bound to paraoxon explains the low sensitivity of this serine hydrolase to organophosphate inactivation.,Montoro-Garcia S, Gil-Ortiz F, Garcia-Carmona F, Polo LM, Rubio V, Sanchez-Ferrer A Biochem J. 2011 Jun 1;436(2):321-30. PMID:21382014 From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See Also Acetylxylan esterase

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