Effects of capping on the non-ionic detergent solubility of rat thymocyte glycoproteins

The non-ionic detergent solubility of surface antigens during capping, following their cross-linking by specific antibodies, was investigated for three rat thymocyte glycoproteins, the leucocyte-common antigen (L-CA), the leucocyte sialoglycoprotein (LSGP) and Thy-1, using a combination of immunofluorescence microscopy, covalent surface radiolabeling and quantitative analysis using a radiolabeled antibody. Prior to the addition of cross-linking antibody, both L-CA and LSGP were soluble in the non-ionic detergent Triton X-100, while Thy-1 was largely insoluble. Addition of sufficient antibody to induce capping led to a significant reduction in the solubility of L-CA and LSGP, even prior to warming to induce capping of the antigen under investigation. Subsequent capping did not increase the amount of insoluble antigen, suggesting that ligand binding, rather than the process of capping itself, is sufficient to cause this partial Triton insolubility. These results indicate the formation of an association between these liganded glycoproteins and the cell's detergent-insoluble cytoskeleton. In contrast, the Thy-1 antigen became progressively more extractable by Triton X-100 as the antigen was capped, suggesting that the insertion of the Thy-1 lipid tail into the plasma membrane was progressively more easily perturbed by the non-ionic detergent during the capping process. The reciprocal maintenance of solubility of either LSGP or L-CA during the capping of the other shows that the majority of the 180 kDa thymocyte L-CA molecules play no role in the mechanism of capping of LSGP. Furthermore, immunoprecipitates of solubilized L-CA contained no detectable amounts of the cytoskeletal protein fodrin.(ABSTRACT TRUNCATED AT 250 WORDS)