p24 and p26, structurally related cell surface molecules identified by monoclonal antibody BA-2

This paper describes additional structural analyses of the p24 cell surface molecule recognized by monoclonal antibody BA-2. Since BA-2 is broadly reactive with a variety of normal and malignant lymphohematopoietic and nonlymphohematopoietic cells, we examined the structure of p24 expressed on different cell types. Tryptic peptide mapping and 2-dimensional gel electrophoresis of p24 isolated from colon carcinoma cells, fresh leukemic cells, leukemic cell lines, and activated T-cells indicated that p24 exhibits no structural polymorphism within the cells examined. As has recently been demonstrated with several other cell surface molecules, p24 is shown to possess a covalently-attached fatty acid, based on the incorporation of [3H]palmitate. We have also identified an additional protein, designated p26, that is coprecipitated with p24. The p26 molecule is not disulfide-linked to p24, and can be immunoprecipitated from a variety of 125I- or [35S]methionine-labeled cells. V8 protease peptide mapping indicated that p24 and p26 are structurally homologous. Pulse-chase analysis using [35S]methionine and digestion with endoglycosidase-F indicated that p24 and p26 are probably derived from a p23 precursor, but no precursor-product relationship exists between p24 and p26. Based on this data we propose that p24 and p26 are most likely differentially-processed protein products of the same gene.

Monoclonal antibody BA-1 recognizes a novel human leukocyte cell surface sialoglycoprotein complex

With the use of the monoclonal antibody BA-1, we have identified and characterized a unique molecular complex on the surface of human B lymphocytes. Despite the marked pronase sensitivity of the BA-1 antigen/epitope on the cell surface, repeated attempts to surface or biosynthetically radiolabel the antigen by using standard protein labeling techniques were unsuccessful. The antigen was identified by immunoprecipitation and sodium dodecyl sulfate-polyacrylamide gel electrophoresis after radiolabeling carbohydrate residues. Surface labeling of galactosyl residues by the neuraminidase/galactose oxidase/3HNaBH4 method revealed a three chain, nondisulfide-linked glycoprotein complex of 45, 55, and 65 kilodaltons (kDa), which we have designated gp45/55/65. Under nonreducing gel conditions there were shifts in the mobility of the 55- and 65-kDa components, consistent with the presence of intrachain disulfide linkages. Surface labeling of sialic acid residues by the sodium periodate/3HNaBH4 method revealed the presence of sialic acid residues on the 45- and 55-kDa components. Two-dimensional gel analysis indicated that the 55-kDa component had an acidic pI of approximately 4.0 and considerable charge heterogeneity, most likely attributable to sialic acid. In contrast, the 45-kDa component had a neutral pI of approximately 7.5. Despite the difficulty in radiolabeling amino acids in gp45/55/65, digestion with V8 protease and pronase clearly demonstrated the presence of protein cores in all three components. Consonant with prior serologic studies with the use of BA-1, we could identify gp45/55/65 on B lymphocytes, B cell precursor acute lymphoblastic leukemias, neutrophils, and eosinophils. This molecular complex has, to our knowledge, not been heretofore described on human B cells and is quite novel in its structure and labeling properties.

Monoclonal antibody BA-1 recognizes a novel human leukocyte cell surface sialoglycoprotein complex

With the use of the monoclonal antibody BA-1, we have identified and characterized a unique molecular complex on the surface of human B lymphocytes. Despite the marked pronase sensitivity of the BA-1 antigen/epitope on the cell surface, repeated attempts to surface or biosynthetically radiolabel the antigen by using standard protein labeling techniques were unsuccessful. The antigen was identified by immunoprecipitation and sodium dodecyl sulfate-polyacrylamide gel electrophoresis after radiolabeling carbohydrate residues. Surface labeling of galactosyl residues by the neuraminidase/galactose oxidase/3HNaBH4 method revealed a three chain, nondisulfide-linked glycoprotein complex of 45, 55, and 65 kilodaltons (kDa), which we have designated gp45/55/65. Under nonreducing gel conditions there were shifts in the mobility of the 55- and 65-kDa components, consistent with the presence of intrachain disulfide linkages. Surface labeling of sialic acid residues by the sodium periodate/3HNaBH4 method revealed the presence of sialic acid residues on the 45- and 55-kDa components. Two-dimensional gel analysis indicated that the 55-kDa component had an acidic pI of approximately 4.0 and considerable charge heterogeneity, most likely attributable to sialic acid. In contrast, the 45-kDa component had a neutral pI of approximately 7.5. Despite the difficulty in radiolabeling amino acids in gp45/55/65, digestion with V8 protease and pronase clearly demonstrated the presence of protein cores in all three components. Consonant with prior serologic studies with the use of BA-1, we could identify gp45/55/65 on B lymphocytes, B cell precursor acute lymphoblastic leukemias, neutrophils, and eosinophils. This molecular complex has, to our knowledge, not been heretofore described on human B cells and is quite novel in its structure and labeling properties.