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 interacts with CD4, inhibits in vitro HIV infection, and triggers cell signaling directly via CD4. Jacalin as a lectin was suggested to trigger CD4-mediated cell signaling by interacting with the oligosaccharide side chains of CD4 located on Asn271 and Asn3OO. Such a hypothesis was of importance because it implied that the glycosylated chains could represent a functional domain directly involved in CD4-related cell activation. We analyzed this possibility by studying the effect of hapten sugars on jacalin-induced CD4 cell signaling and jacalin/CD4 interaction, and by studying the binding capacities of the lectin toward glycosylated, deglycosylated, and unglycosylated CD4. The results presented in this study provide evidence that jacalin does not recognize the 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 signaling triggered by the lectin.