Chloramphenicol acetyltransferase structure

The major mechanism of resistance to chloramphenicol is mediated by the chloramphenicol acetyltransferases (CAT enzymes) which transfer one or two acetyl groups to one molecule of chloramphenicol. While the CAT enzymes share a common mechanism, different molecular classes can be discriminated. The corresponding genes are frequently located on integron-like structures and are widely distributed among Gramnegative and - positive bacteria. 

Strategically similar, but structurally distinct, are the chloramphenicol acetyltransferases (CATs). Chloramphenicol binds to the large ribosomal subunit at the nexus of the peptidyltraus-fer ceuter aud the peptide exit muuel (28, 29). CATs are trimeric euzymes with active sites at the iuterface of the monomers... 

Leslie AG, Moody PC, Shaw WV. Structure of chloramphenicol acetyltransferase at 1.75-A resolution. Proc. Natl. Acad. Sci. 

FIGURE 8,8 Catalytic mechanism of chloramphenicol acetyltransferase. The catalytic model features His-195 as the general base initiating the catalysis which involves a tetrahedral intermediate (the structure in parentheses). The oxyanion of the tetrahedral intermediate is thought to be stabilized by two H-bonds one with the OH group of Ser-148 and the other with a water molecule (water 252) bound to Thr-174. 

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