Carbohydrate Complexity of the Mouse Thymocyte Thy‐1 Glycoprotein as Demonstrated by Lectin Affinity and Isoelectric Focusing

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Abstract
The Thy-1 glycoprotein of mouse thymocytes was analyzed with regard to the properties of its cabohydrate part. Of the different lectins tested, partial binding of Thy-1 from membrane extracts was found to Lens culinaris agglutinin (.apprx. 50%) and wheat germ agglutinin (.apprx. 25%). Concanavalin A bound all Thy-1. There is considerable microheterogeneity in the oligosaccharide 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 6 charge variants (isoelectric points ranging from 5-9). These variants were isolated, treated with neuraminidase and tested for lectin binding and isoelectric point. The charge heterogeneity was due to different amounts of sialic acid; even the most basic form contained at least 1 sialic acid residue. The degree of siaylation was apparently not correlatd to the lectin-binding properties. Analysis of Thy-1 from surface 125I-labeled 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.