Identification of peanut agglutinin-binding glycoproteins on immature human thymocytes

Previous studies in our laboratory have shown that peanut agglutinin (PNA), a lectin specific for the disaccharide Galβ3GalNAc, binds to immature (cortical) thymocytes of mouse and man and not to the mature (medullary) cells. Using lectin overlay of protein blots and lectin-affinity chromatography, we have found that the major PNA-binding glycoproteins on total as well as on immature (PNA⁺) human thymocytes correspond to two bands of M_r 170,000 and 180,000. Another glycoprotein, of M_r 110,000, also binds PNA but to a lesser extent. All three glycoproteins contain sialic acid as demonstrated by cell surface labeling with NaIO₄NaB³H₄, binding of wheat germ agglutinin, and reaction with alkaline phosphatase-hydrazide. After treatment with sialidase, binding of PNA to these glycoproteins is significantly enhanced.