Lactose binding to the E. coli symport protein Lac permease

Lac permease is a symport protein which responsible for the active accumulation of lactose in E. coli. The protein utilizes the energy from the downhill translocation of protons to drive uphill accumulation of lactose. This work reports the direct measurement by proton NMR of lactose binding to lac permease of E. coli membrane vesicles. The technique allows the determination of the K_d of lactose binding to lac permease binding sites. The results presented here show that the assay is specific for lac permease binding sites and that the assay can distinguish differences in binding affinity for different site specific mutants of lac permease. Determination of the Kd for lactose binding is important in determining which residues are important for lactose binding.