Differential galactosylation of neuronal and haematopoietic signal regulatory protein-alpha determines its cellular binding-specificity

Signal regulatory protein-alpha (SIRP alpha) is a member of the Ig superfam ily selectively expressed by neuronal and myeloid cells, The molecule media tes functional interactions with CD47/integrin-associated protein, Here we provide evidence for the tissue-specific glycosylation of neuronal and haem atopoietic SIRP alpha. We demonstrate a major difference in the galactosyla tion of N-linked glycans isolated from neuronal (i.e. brain-derived) SIRP a lpha as compared to myeloid (i.e. spleen-derived) SIRP alpha, with neuronal SIRP alpha almost completely lacking galactose, beta4-galactosyltransferas e assays demonstrated that this is most likely due to a tow galactosylation capacity of the brain, In order to investigate the role of galactosylation of SIRP alpha in cellular Interactions, soluble recombinant SIRP alpha gly coforms containing galactose (SIRP alpha -Fc) or lacking galactose (SIRP al pha(Delta Gal)-Fc) were produced, Binding studies demonstrated superior bin ding of SIRP alpha(Delta Gal)Fc to cerebellar neurons and isolated lymphocy tes. In contrast, SIRP alpha -Fc bound relatively strong to macrophages, Th ese data show that the galactosylation of SIRP alpha determines its cellula r binding specificity.