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.