The acylation mechanism of CTX-M β-lactamase at 0.88 Å resolution

The apo crystal structure of CTX-M-9 beta-lactamase has been determined to 0.88 A at pH 8.8. This unusually clear picture of proton positions and residue interactions supports the role of Glu166 as the general base for the controversial acylation step of class A beta-lactamase catalysis. The ability to distinguish low-energy conformations sampled by the enzyme allows us to link the two conformations of Lys73 to different protonation states of Glu166.