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 lym phocytes obtained from the different lymphoid organs. Direct immunoflu orescence assays have demonstrated that the majority of lizard thymocy tes (70%) and only a fraction of lymphocytes in the spleen, peripheral blood and bone marrow were PNA-positive. This positivity was selectiv ely inhibited by galactose as well as lactose, indicating the specific ity of binding. Putative PNA receptors were purified from lizard thymo cytes and splenocytes by affinity chromatography on a PNA-Sepharose 4B column and resulted in fractions enriched 1,792-fold and 3,141-fold f or the PNA-binding component expressed on lizard thymocytes and spleno cytes, respectively. Analysis on reducing and non-reducing SDS-PAGE re vealed 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 ca rbohydrate compositions indicated that the thymic and splenic glycopro teins 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 recep tor compared to its thymic counterpart, and was inversely correlated w ith the content of galactosyl residues in both forms of the receptor. The functional significance of PNA-binding glycoproteins during verteb rate evolution is discussed.