Hemophilic interaction of junctional adhesion molecule

Junctional adhesion molecule (JAM) is an integral membrane protein that bel ongs to the immunoglobulin superfamily, localizes at tight junctions, and r egulates both paracellular permeability and leukocyte transmigration. To in vestigate molecular determinants of JAM function, the extracellular domain of murine JAM was produced as a recombinant soluble protein (rsJAM) in inse ct cells, rsJAM consisted in large part of noncovalent homodimers, as asses sed by analytical ultracentrifugation, JAM dimers were also detected at the surface of Chinese hamster ovary cells transfected with murine JAM, as eva luated by cross-linking and immunoprecipitation. Furthermore, fluid-phase r sJAM bound dose-dependently solid-phase rsJAM, and such hemophilic binding was inhibited by anti-JAM Fab BV11, but not by Fab BV12, Interestingly, Fab BV11 exclusively bound rsJAM dimers (but not monomers) in solution, wherea s Fab BV12 bound both dimers and monomers, Finally, we mapped the BV11 and BV12 epitopes to a largely overlapping sequence in proximity of the extrace llular amino terminus of JAM, me hypothesize that rsJAM dimerization induce s a BV11-positive conformation which in turn is critical for rsJAM hemophil ic interactions. Dimerization and hemophilic binding may contribute to both adhesive function and junctional organization of JAM.