Abstract
The functional consequences of glycan structural changes associated with cellular differentiation are ill defined. Herein, we investigate the role of glycan adducts to the O-glycosylated polypeptide stalk tethering the CD8αβ coreceptor to the thymocyte surface. We show that immature CD4+CD8+ double-positive thymocytes bind MHCI tetramers more avidly than mature CD8 single-positive thymocytes, and that this differential binding is governed by developmentally programmed O-glycan modification controlled by the ST3Gal-I sialyltransferase. ST3Gal-I induction and attendant core 1 sialic acid addition to CD8β on mature thymocytes decreases CD8αβ-MHCI avidity by altering CD8αβ domain-domain association and/or orientation. Hence, glycans on the CD8β stalk appear to modulate the ability of the distal binding surface of the dimeric CD8 globular head domains to clamp MHCI.
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