Coordinated binding of sugar, calcium, and antibody to macrophage C-type lectin.
Mouse macrophage galactose/N-acetylgalactosamine-specific C-type lectin (MMGL) is a type II transmembrane glycoprotein belonging to the C-type lectin family. Our development of monoclonal antibodies led us to discover that a calcium-dependent conformational change is detected by an antibody (termed mAb LOM-11) and that the antibody's binding to the respective site locks the lectin in an active conformation. These findings correspond to the divalent cation-mediated regulatory mechanisms in a family of cell adhesion molecule integrins that have gained much attention. We now provide direct evidence that mAb LOM-11 increases the affinity of the lectin for calcium ions as a mechanism for the conformational lock using a soluble recombinant form of MMGL (rML) produced in bacteria. Furthermore, we discovered by using an enzyme-linked immunosorbent assay that specific monosaccharides induced a binding site for mAb LOM-11 on the immobilized rML under low calcium environments. We also demonstrated that cell surface MMGL on a transfectant cell line underwent a conformational change upon addition of calcium or ligands, as detected by the binding of mAb LOM-11. These properties are reminiscent of ligand-induced binding sites defined for integrins. The present results suggest a possibility that the mAb LOM-11 binding site on the lectin may be a site at which protein-protein interaction helps to fine tune the specificity of the C-type lectins by means of coordinated recognition mechanisms.
Hosoi
T
T
Laboratory of Cancer Biology and Molecular Immunology, Graduate School of Pharmaceutical Sciences, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan.
Imai
Y
Y
Irimura
T
T
D000818:Animals; D000911:Antibodies, Monoclonal / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism*; D002460:Cell Line; D000939:Epitopes / Q000378:metabolism; D037102:Lectins / Q000276:immunology / Q000378:metabolism*; D037181:Lectins, C-Type; D008565:Membrane Proteins / Q000276:immunology / Q000378:metabolism*; D051379:Mice; D009005:Monosaccharides / Q000378:metabolism*; D051381:Rats
D000911:Antibodies, Monoclonal; C113583:Clecsf8 protein, mouse; D000939:Epitopes; D037102:Lectins; D037181:Lectins, C-Type; D008565:Membrane Proteins; D009005:Monosaccharides; D002118:Calcium