Antibody-Mediated Modification of the Binding Properties of a Protein Related to Galactose Transport

A galactose-binding protein related to themglP transport system ofEscherichia coli increases its affinity and binding capacity for the substrate when exposed to bothd -galactose and specific antibodies. For this increase to occur, the binding protein has to be in contact withd -galactose for at least 2 min prior to the addition of the antibodies. This reaction was used to show that other substrates of themglP transport system compete with galactose for a site(s) of the binding protein and that the degree of competition is comparable to that observed in vivo. A model for substrate translocation is presented postulating a cellular component that can induce conformational changes in the galactose-binding protein similar to those caused by antibodies.