Title : A single N-linked glycosylation
site is implicated in the regulation of ligand recognition by the I-type lectins
CD22 and
CD33
Abstract :
- CD22 is an immunoglobulin superfamily B lymphocyte-specific adhesion receptor and a member of the recently identified I-type class of lectins
- Recent work has shown that CD22 specifically recognizes sialic acid linked alpha2,6 to terminal N-linked oligosaccharides on selected cell surface glycoproteins
- CD22-ligand interaction is regulated by the activity of a beta-galactoside alpha2 , 6-sialyltransferase that can inactivate CD22-mediated binding by sialylating the CD22 receptor itself
- These observations suggest that N-linked glycosylation sites on the CD22 molecule may play a role in the regulation of CD22-mediated adhesion
- In this work we have performed site-specific mutagenesis of potential N-linked glycosylation sites on CD22 in an effort to determine whether they might be involved in ligand recognition
- We show that mutation of a single potential N-linked glycosylation site in the first immunoglobulin domain of CD22 completely abrogates ligand recognition
- Interestingly, this site is characterized by the sequence NCT, where the cysteine is thought to be involved in an intra chain disulfide bond
- Site-directed mutagenesis of similar NC(T/S) motifs in the first or second Ig domains of the I-type lectins myelin-associated glycoprotein , and sialoadhesin did not disrupt their ability to mediate sialic acid binding.
- In contrast, mutation of a NCS motif in the first Ig domain of the I-type lectin CD33 unmasked its sialic acid binding activity.
- These observations suggest that a single N-linked glycosylation site located at a similar position in the CD22 and CD33 glycoproteins is critical for regulating ligand recognition by both receptors