Two-dimensional electrophoretic analysis of concanavalin-A binding components in the plasma membranes of Chinese hamster fibroblasts

Topography of the total protein population from cultured cells upon fractionation by chemical extractions

Chemical extractions are proposed as a major tool for a fractionation of cellular proteins. As a model system, proteins from cultured hamster lens cells have been divided by independent extractions into seven subcellular fractions, corresponding to water-soluble proteins and the proteins from membranes, microfilaments (and other deoxycholate-soluble proteins), intermediate filaments, microtubules, polysomes and nuclei respectively. The latter two fractions have been subfractionated yielding ribosomal proteins, the elongation and initiation factors of the protein-synthesis machinery, chromatin proteins and non-chromatin proteins. The protein compositions of the fractions have been analyzed by one-dimensional and two-dimensional gel electrophoresis. This resulted in an almost complete topography of the proteins detected on two-dimensional gels of total-cell lysates. Comparison of two-dimensional patterns of proteins from the total-cell lysate and proteins from hamster erythrocytes or from liver, muscle or brain tissue showed that the different cell types have only few proteins in common. Two proteins are common to all of these cell types, namely actin and a 68-kDa protein. The latter protein was, like actin, vimentin and the tubulin subunits, also present in most cell fractions. Evidence is presented that this protein is identical to a 68-kDa heat-shock protein.

A simple method for electrophoretic analysis of cell surface glycoproteins based on concanavalin A binding

A simple and sensitive method is described for the detection of cell surface proteins. This method consists of reacting concanavalin A (Con A) with 35S-labeled methionine, detergent solubilized whole cell extracts and immunoprecipitating the Con A-protein complexes with anti-Con A antibody bound to Staphylococcus aureus Cowan I strain (SACI). These reagents are commercially available, stable and easy to standardize. Mouse lymphocytes cell surface proteins purified by this procedure show great similarities to those purified with goat anti-cell surface antibodies.

Isolation of a domain of the plasma membrane in Chinese hamster ovary cells which contains iodinatable, acidic glycoproteins of high molecular weight

A light vesicle fraction, apparently derived from the plasma membrane, was obtained following breakage of Chinese hamster ovary (CHO) cells by means of a fluid pump disrupting device. The final preparation was enriched approx. 40-fold over the homogenate in K+,Na+-stimulated ATPase and phosphodiesterase I, but only approx. 10-fold in 125I specific radioactivity after lactoperoxidase-catalyzed iodination. This preparation was compared with another plasma membrane fraction purified as large sheets via a two-phase centrifugation procedure. Two-dimensional polyacrylamide gel electrophoresis followed by Coomassie blue staining indicated that both fractions were fairly similar in polypeptide composition, although a few consistent differences were evident. However, staining of glycoproteins by the periodic acid-Schiff technique or by overlaying with 125I-labeled concanavalin A showed that the vesicle fraction was highly enriched in groups of high molecular weight, acidic glycoproteins which stain only weakly with Coomassie blue. These glycoproteins also bound 125I-labeled ricin I agglutinin and wheat germ agglutinin. They appear to be the major receptors for wheat germ agglutinin on the CHO cell surface. After surface labeling of cells by the 125I-lactoperoxidase technique, the membrane sheet fraction contained a large number of iodinated polypeptides, whereas labeling in the vesicle fraction was restricted almost entirely to the high molecular weight, acidic glycoproteins. It is proposed that the vesicle fraction constitutes a specific domain of the cell surface which is coated on its exterior by this group of glycoproteins. These components probably mask underlying proteins of the plasma membrane from external labeling.