STRUCTURAL CHARACTERIZATION OF A LOW-MOLECULAR-WEIGHT RECEPTOR FOR PEANUT AGGLUTININ IN MURINE LYMPHOCYTES

A novel low molecular weight (LMW) receptor for the lectin peanut aggl utinin (PNA) was characterized and purified from murine thymocytes and peripheral lymphocytes in the spleen. Preliminary binding assays with the fluoresceinated lectin demonstrated that the majority of cortical thymocytes, and only a fraction of lymphocytes in the splenic white p ulp, as well as other peripheral lymphoid organs were PNA-positive. Th is positivity was selectively inhibited by the preferred PNA disacchar ide ligand (Gal beta 1,3GalNAc), indicating the specificity of the bin ding. PNA receptors were purified from thymocytes and splenocytes by a ffinity chromatography on a PNA-agarose column, and their structural c haracteristics assessed by treatments with endoglycosidases and alkali ne borohydride and analysis by two-dimensional (2-D) gels. Comparisons based on 2-D gels of glycosylated and deglycosylated forms were consi stent with the thymic and splenic receptors, sharing a common 21 kDa p olypeptide backbone, which is subjected to differential post-translati onal N-linked glycosylations with one (thymic PNA receptor) or two and /or three (splenic PNA receptor) complex-type glycan units of distinct structures. Analyses of amino acid and carbohydrate compositions of t he intact receptors confirmed these observations and revealed a compar atively high level of sialic acid residues in the splenic PNA receptor .