Identification of peanut agglutinin-binding glycoproteins on lizard lymphocytes

The expression of PNA-binding glycoproteins on lizard lymphocytes was investigated by studying the reactivity of FITC-PNA towards lizard lymphocytes obtained from the different lymphoid organs. Direct immunofluorescence assays have demonstrated that the majority of lizard thymocytes (70%) and only a fraction of lymphocytes in the spleen, peripheral blood and bone marrow were PNA-positive. This positivity was selectively inhibited by galactose as well as lactose, indicating the specificity of binding. Putative PNA receptors were purified from lizard thymocytes and splenocytes by affinity chromatography on a PNA-Sepharose 4B column and resulted in fractions enriched 1,792-fold and 3,141-fold for the PNA-binding component expressed on lizard thymocytes and splenocytes, respectively. Analysis on reducing and non-reducing SDS-PAGE revealed that both thymic and splenic PNA-binding glycoproteins migrated as a single component of 35 KDa, with no evidence for the association into higher multimers in both tissues. Analyses for amino acid and carbohydrate compositions indicated that the thymic and splenic glycoproteins have similar amino acid composition and differed in the content of neutral and amino-sugars as well as sialic acid. The content of the latter residue was relatively higher in the splenic form of the receptor compared to its thymic counterpart, and was inversely correlated with the content of galactosyl residues in both forms of the receptor. The functional significance of PNA-binding glycoproteins during vertebrate evolution is discussed.