4ua9

CTX-M-14 Class A Beta-Lactamase in Complex with a Boronic Acid Acylation Transition State Analog at Sub-Angstrom Resolution

spinqualitylabelsall models 4ua9, resolution 0.84Å Show:Asymmetric Unit Biological Assembly Drag the structure with the mouse to rotate   Export Animated Image   Print3D Structural highlights 4ua9 is a 2 chain structure with sequence from Escherichia coli. Full crystallographic information is available from OCA. For a guided tour on the structure components use FirstGlance. Method: X-ray diffraction, Resolution 0.84Å Ligands: CB4, PCA, PO4 Resources: FirstGlance, OCA, PDBe, RCSB, PDBsum, ProSAT Function H6UQI0_ECOLX Publication Abstract from PubMed Ligand binding can change the pKa of protein residues and influence enzyme catalysis. Herein, we report three ultrahigh resolution X-ray crystal structures of CTX-M beta-lactamase, directly visualizing protonation state changes along the enzymatic pathway: apo protein at 0.79 A, precovalent complex with nonelectrophilic ligand at 0.89 A, and acylation transition state (TS) analogue at 0.84 A. Binding of the noncovalent ligand induces a proton transfer from the catalytic Ser70 to the negatively charged Glu166, and the formation of a low-barrier hydrogen bond (LBHB) between Ser70 and Lys73, with a length of 2.53 A and the shared hydrogen equidistant from the heteroatoms. QM/MM reaction path calculations determined the proton transfer barrier to be 1.53 kcal/mol. The LBHB is absent in the other two structures although Glu166 remains neutral in the covalent complex. Our data represents the first X-ray crystallographic example of a hydrogen engaged in an enzymatic LBHB, and demonstrates that desolvation of the active site by ligand binding can provide a protein microenvironment conducive to LBHB formation. It also suggests that LBHBs may contribute to stabilization of the TS in general acid/base catalysis together with other preorganized features of enzyme active sites. These structures reconcile previous experimental results suggesting alternatively Glu166 or Lys73 as the general base for acylation, and underline the importance of considering residue protonation state change when modeling protein-ligand interactions. Additionally, the observation of another LBHB (2.47 A) between two conserved residues, Asp233 and Asp246, suggests that LBHBs may potentially play a special structural role in proteins. Ligand-Induced Proton Transfer and Low-Barrier Hydrogen Bond Revealed by X-ray Crystallography.,Nichols DA, Hargis JC, Sanishvili R, Jaishankar P, Defrees K, Smith EW, Wang KK, Prati F, Renslo AR, Woodcock HL, Chen Y J Am Chem Soc. 2015 Jun 22. PMID:26057252 From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See Also Beta-lactamase 3D structures

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