Characterization of the laminin binding domains of the Lutheran blood group glycoprotein

Lutheran (Lu) blood group antigens and the basal cell adhesion molecule ant igen reside on two glycoproteins that belong to the Ig superfamily (IgSF) a nd carry five Ig-like extracellular domains. These glycoproteins act as wid ely expressed adhesion molecules and represent the unique receptors for lam inin-10/11 in erythroid cells. Here, we report the mapping of IgSF domains responsible for binding to laminin, In plasmonic resonance surface experime nts, only recombinant Lu proteins containing the N-terminal IgSF domains 1- 3 were able to bind laminin-10/11 and to inhibit binding of laminin to Lu-e xpressing K562 cells. Mutant recombinant proteins containing only IgSF doma in 1, domains 1 + 2, domains 1 + 3, domains 2 + 3, domain 3, domain 4, doma in 5, and domains 4 + 5 failed to bind laminin as well as a construct conta ining all of the extracellular domains except domain 3, Altogether, these r esults indicate that IgSF domains 1-3 are involved in laminin binding and t hat a specific spatial arrangement of these three first domains is most pro bably necessary for interaction. Nei ther the RGD nor the N-glycosylation m otifs present in IgSF domain 3 were involved in laminin binding.