Structure of the lac operon galactoside acetyltransferase.
The galactoside acetyltransferase (thiogalactoside transacetylase) of Escherichia coli (GAT, LacA, EC 2.3.1.18) is a gene product of the classical lac operon. GAT may assist cellular detoxification by acetylating nonmetabolizable pyranosides, thereby preventing their reentry into the cell. The structure of GAT has been solved in binary complexes with acetyl-CoA or CoA and in ternary complexes with CoA and the nonphysiological acceptor substrates isopropyl beta-D-thiogalactoside (IPTG) or p-nitrophenyl beta-D-galactopyranoside (PNPbetaGal). A hydrophobic cleft that binds the thioisopropyl and p-nitrophenyl aglycones of IPTG and PNPbetaGal may discriminate against substrates with hydrophilic substituents at this position, such as lactose, or inducers of the lac operon. An extended loop projecting from the left-handed parallel beta helix domain contributes His115, which is in position to facilitate attack of the C6-hydroxyl group of the substrate on the thioester.
Wang
Xing-Guo
XG
Department of Biochemistry, Albert Einstein College of Medicine, 1300 Morris Park Avenue, Bronx, NY 10461, USA.
Olsen
Laurence R
LR
Roderick
Steven L
SL
D000123:Acetyltransferases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D001665:Binding Sites; D018360:Crystallography, X-Ray; D004926:Escherichia coli / Q000201:enzymology; D007763:Lac Operon; D046911:Macromolecular Substances; D008958:Models, Molecular; D017434:Protein Structure, Tertiary; D016415:Sequence Alignment
D001426:Bacterial Proteins; D046911:Macromolecular Substances; D000123:Acetyltransferases; C022770:galactoside acetyltransferase