Transporter structure and mechanism.

During the past several decades, lac permease has assumed almost tutelary proportions as a model for cotransporters. This archetypical membrane protein now exerts its influence by the most dramatic means possible: its structure is solved. This article describes the configuration and implied transport mechanism of the bacterial lactose transporter and compares its structure and function with those of other transporters and those of ion channels. This juxtaposition of transporters and channels is likely to be helpful because LacY is the first cotransporter with known structure and exclusive carrier properties, and it shares topology with neurotransmitter transporters with unknown structure and channel properties.