• DOI:10.1042/BST0160939
• Corpus ID: 20488545

Tinkering with antibiotic resistance: chloramphenicol acetyltransferase and its substrates.

@article{Shaw1988TinkeringWA,
  title={Tinkering with antibiotic resistance: chloramphenicol acetyltransferase and its substrates.},
  author={William V. Shaw and Philip J. Day and Ann Lewendon and Iain A. Murray},
  journal={Biochemical Society transactions},
  year={1988},
  volume={16 6},
  pages={
          939-42
        }
}

• W. V. Shaw, P. Day, +1 author I. Murray
• Published 1 December 1988
• Chemistry, Biology
• Biochemical Society transactions

Chloraniphcnicol acctyltransfcrase ( C A T ) ( E C 7.3.1.78) catalyses the 0-acetylation and inactivation of the antibiotic, using acetyl-CoA a s the acyl donor. T h e structural gene for CAT in chlor~rmphenicol-resistant bacteria may be chromosomal. hut in most genera has been observed t o be plasmidborne. All known variants have similar subunit molecular masses ( 75 k l h ) and a high degree o f sequence homology, indicative of a common tertiary structure (Shaw & Leslie, I YSS). The so-called type I enzyme. associated with transposon TnO and ;I variety o f F-like R plasmids, is the most frequently encountered natural CAT variant in Gram-negative bnctcria. A less commonly observed member of the entcric C'AY family. a type 111 variant. has proved t o he a particularly iiseful model system for protein engineering and the study of determinants o f molecular recognition (Murray ct (11.. I988). The tertiary structure o f a type 111 CAT has been determined by X-ray diffraction and shown it t o he a trinier o f identical subunits. with the active sites located at the three subunit interfaces ( lxsl ie ct d . 19881. T h e slructure o f the native trimcr and its binary complex with chloramphenicol are known at 0.1 75 nm resolution. and the structure o f CAT with CoA hound has been refined ;it 0.24 nm resolution. Since ('AT hinds chloramphenicol with the same specificity ;IS the pcptidyl transferase centre o f prokaryotic ribosomes, the elusive target for the antibiotic's action, there is a sense in which CAT may be seen ;IS ii 'siirrogate' receptor for ligandbinding studies (ShaN. 198.3). T h e results o f steady-state kinetic studies had previously suggested that the mechanism of CAT is likely t o be a sequential one. wherein ;I ternary complex o f CAT. chloramphenicol. and acetyl-CoA is formed by thc random order o f addition o f substrates (Kleanthous & Shaw. 1984). The reaction was shown to be freely reversible, although the forward reaction is favoured because of the difference in free energies o f hydrolysis o f acetyl-CoA and acctyl chloramphenicol: Chloramphenicol + acetyl-S-CoA = 3-0-acetyl chloramphenicol + CoASH ( 1 )