A study of the interactions of an immunoglobulin light chain with artificial and B-lymphocyte membranes

The binding of an immunoglobulin lambda light chain (IgLC) to synthetic and biological membranes was monitored in real-time using a recently developed, time-resolved fluorescence technique. Lambda IgLC purified from the urine of patients with multiple myeloma, were used in studies of protein-membrane interactions. The association of the lambda IgLC dimer with B-lymphocytes was shown to be stabilised predominantly by non-polar interactions. Furthermore, it was found that following binding to synthetic phospholipid membranes, a reorientation of the light chain occurred which resulted in a change in the distribution of charged residues at the lipid-water interface. The rate constants associated with the binding event were calculated, and appear to comprise both temperature insensitive and sensitive components. The calculated activation energies of the binding and reorientation events were found to be 13.53 KJmol(-1) and 87.89 KJmol(-1), respectively. The large activation energy associated with the reorientation phase suggests the movement of large protein domains, possibly involving a whole immunoglobulin domain. The binding and reorganisation of the IgLC upon the phospholipid membrane may confer novel biological functions to the bound protein and potentially contribute to such phenomenon as myeloma-associated immuno-suppression.