title: Purification of a high molecular weight actin filament gelation protein from Acanthamoeba that shares antigenic determinants with vertebrate spectrins.
abstract: I have purified a high molecular weight actin filament gelation protein (GP-260) from Acanthamoeba castellanii, and found by immunological cross-reactivity that it is related to vertebrate spectrins, but not to two other high molecular weight actin-binding proteins, filamin or the microtubule-associated protein, MAP-2. GP-260 was purified by chromatography on DEAE-cellulose, selective precipitation with actin and myosin-II, chromatography on hydroxylapatite in 0.6 M Kl, and selective precipitation at low ionic strength. The yield was 1-2 micrograms/g cells. GP-260 had the same electrophoretic mobility in SDS as the 260,000-mol-wt alpha-chain of spectrin from pig erythrocytes and brain. Electron micrographs of GP-260 shadowed on mica showed slender rod-shaped particles 80-110 nm long. GP-260 raised the low shear apparent viscosity of solutions of Acanthamoeba actin filaments and, at 100 micrograms/ml, formed a gel with a 8 microM actin. Purified antibodies to GP-260 reacted with both 260,000- and 240,000-mol-wt polypeptides in samples of whole ameba proteins separated by gel electrophoresis in SDS, but only the 260,000-mol-wt polypeptide was extracted from the cell with 0.34 M sucrose and purified in this study. These antibodies to GP-260 also reacted with purified spectrin from pig brain and erythrocytes, and antibodies to human erythrocyte spectrin bound to GP-260 and the 240,000-mol-wt polypeptide present in the whole ameba. The antibodies to GP-260 did not bind to chicken gizzard filamin or pig brain MAP-2, but they did react with high molecular weight polypeptides from man, a marsupial, a fish, a clam, a myxomycete, and two other amebas. Fluorescent antibody staining with purified antibodies to GP-260 showed that it is concentrated near the plasma membrane in the ameba.
mesh_terms: D000656:Amoeba / Q000032:analysis*; D000818:Animals; D002352:Carrier Proteins; D002645:Chickens; D004591:Electrophoresis, Polyacrylamide Gel; D000939:Epitopes / Q000032:analysis*; D005455:Fluorescent Antibody Technique; D005782:Gels; D005895:Gizzard, Avian; D008840:Microfilament Proteins / Q000276:immunology / Q000302:isolation & purification*; D008854:Microscopy, Electron; D008970:Molecular Weight; D013045:Species Specificity; D013049:Spectrin / Q000276:immunology; D013329:Structure-Activity Relationship
chemical_list: D002352:Carrier Proteins; D000939:Epitopes; C034037:F-actin-binding proteins; D005782:Gels; D008840:Microfilament Proteins; D013049:Spectrin