The Role of Glycosylation on the Spatiotemporal Organization and Function of B-cell Co-receptor CD22

An important inhibitory co-receptor on B-cells is CD22, a sialic-acid binding protein. CD22 is highly glycosylated with six glycans located in the first two extracellular domains. The cytosolic domain contains ITIMs that upon phosphorylation lead to recruitment of inhibitory phosphatase SHP-1. Proximity of CD22 to B cell receptor (BCR) is required for dephosphorylation of signalling molecules leading to signal attenuation; however, we do not understand what mediates CD22 organization and association to BCRs. Since glycans on CD22 can be terminally sialylated, we hypothesize these glycans facilitate homotypic CD22 interactions, and therefore affect CD22 heterotypic interaction with BCRs. Here, we utilized a N-terminal glycosylation mutant (5Q-CD22) and, using super-resolution imaging, we demonstrate that 5Q-CD22 displays increased clustering and closer association to IgM BCR compared to WT-CD22. Importantly, abrogation of these glycans leads to loss of CD22 function, as ITIM phosphorylation upon B-cell activation is decreased and consequently BCR signalling is enhanced.M.Sc