Practice question

lacA encodes beta-galactoside transacetylase, 203-amino-acid enzyme transferring acetyl group from acetyl-CoA donor to C6 hydroxyl acceptor of thiogalactosides and non-metabolizable lactose analogs. Crystallographic analysis reveals left-handed beta-helix fold assembled as trimer with active sites at subunit interfaces. Physiological role appears detoxification rather than primary catabolism: acetylation prevents accumulation of disulfide-forming thiogalactosides or other potentially toxic beta-galactosides that could irreversibly modify cellular proteins or glutathione, promoting their efflux via other transporters. Deletion mutants remain fully viable on lactose because hydrolysis by beta-galactosidase suffices, indicating auxiliary protective role rather than central catabolic requirement.