Carbohydrate complexity of the mouse thymocyte Thy-1 glycoprotein as demonstrated by lectin affinity and isoelectric focusing.

The Thy-1 glycoprotein of mouse thymocytes was analysed with regard to the properties of its carbohydrate part. Of the different lectins tested, partial binding of Thy-1 from membrane extracts was found to Lens culinaris agglutinin (approximately 50%) and wheat germ agglutinin (approximately 25%). In contrast, concanavalin A bound all Thy-1. The results indicate that there is considerable microheterogeneity in the oligosaccaride chains within the Thy-1 population. Thy-1 was purified from thymocyte membrane extracts by concanavalin A affinity chromatography and gel filtration. The purified preparation revealed, on analysis by isoelectric focusing, at least six charge variants (isoelectric points ranging from approximately 5-9). These variants were isolated, treated with neuraminidase and tested for lectin binding and isoelectric point. It was shown that the charge heterogeneity was due to different amounts of sialic acid; even the most basic form contained at least one sialic acid residue. Furthermore, it was concluded that the degree of sialylation was not correlated to the lectin-binding properties. Analysis of Thy-1 from surface 125I-labelled thymocytes showed that the purified preparation was representative in its complexity of the Thy-1 glycoprotein exposed on the surface membrane. The possible biological implications of the findings are discussed.