Monoclonal antibody 4B1 influences the pK of Glu325 in lactose permease (LacY) from Escherichia coli: evidence from SEIRAS.

The monoclonal antibody 4B1 binds to a conformational epitope on the periplasmic side of lactose permease (LacY) of Escherichia coli and inhibits H /lactose symport and lactose efflux under nonenergized conditions. At the same time, ligand binding and translocation reactions that do not involve net H translocation remain unaffected by 4B1. In this study, surface-enhanced infrared absorption spectroscopy applied to the immobilized LacY was used to study the pH-dependent changes in LacY and to access in situ the effect of the 4B1 antibody on the pK of Glu325, the primary functional H -binding site in LacY. A small shift of the pK value from 10.5 to 9.5 was identified that can be corroborated with the inactivation of LacY upon 4B1 binding.