| Description | Chloramphenicol acetyltransferase (CAT) ( ) [ ] catalyzes the acetyl-CoA dependent acetylation of chloramphenicol (Cm), an antibiotic which inhibits prokaryotic peptidyltransferase activity. Acetylation of Cm by CAT inactivates the antibiotic. The pattern signature for this entry contains the histidine residue, located in the C-terminal section of the enzyme, that plays a central role in its catalytic mechanism.There is a second family of CAT [ ], evolutionary unrelated to the main family described above. These CAT belong to the bacterial hexapeptide-repeat containing-transferases family (see ). The crystal structure of the type III enzyme from Escherichia coli with chloramphenicol bound has been determined. CAT is a trimer of identical subunits (monomer Mr 25,000) and the trimeric structure is stabilised by a number of hydrogen bonds, some of which result in the extension of a β-sheet across the subunit interface. Chloramphenicol binds in a deep pocket located at the boundary between adjacent subunits of the trimer, such that the majority of residues forming the binding pocket belong to one subunit while the catalytically essential histidine belongs to the adjacent subunit. His195 is appropriately positioned to act as a general base catalyst in the reaction, and the required tautomeric stabilisation is provided by an unusual interaction with a main-chain carbonyl oxygen [ ].This signature pattern covers the region surrounding an active site histidine residue located in the C-terminal section of the enzyme; this residue plays a central role in its catalytic mechanism. | Name | Chloramphenicol acetyltransferase, active site |
| Short Name | Chloramphenicol_AcTrfase_AS | Type | Active_site |
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