THE LECTIN JACALIN TRIGGERS CD4-MEDIATED LYMPHOCYTE SIGNALING BY BINDING CD4 THROUGH A PROTEIN-PROTEIN INTERACTION

The lectin jacalin specifically stimulates lymphocytes expressing the CD4 antigen, Recent studies have also demonstrated that this lectin in teracts with CD4, inhibits in vitro HIV infection, and triggers cell s ignaling directly via CD4, Jacalin as a lectin was suggested to trigge r CD4-mediated cell signaling by interacting with the oligosaccharide side chains of CD4 located on Asn(271) and Asn(300), Such a hypothesis was of importance because it implied that the glycosylated chains cou ld represent a functional domain directly involved in CD4-related cell activation, We analyzed this possibility by studying the effect of ha pten sugars on jacalin-induced CD4 cell signaling and jacalin/CD4 inte raction, and by studying the binding capacities of the lectin toward g lycosylated, deglycosylated, and unglycosylated CD4, The results prese nted in this study provide evidence that jacalin does not recognize th e CD4 oligosaccharide chains and actually binds CD4 through a specific protein-protein interaction; as a consequence these results rule out the involvement of the CD4 saccharide moieties in CD4-mediated cell si gnaling triggered by the lectin.