Filamin, a new high-molecular-weight protein found in smooth muscle and nonmuscle cells. Purification and properties of chicken gizzard filamin

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Abstract
Filamin, a major high MW protein of chicken gizzard smooth muscle, was purified to homogeneity by salt extraction, ammonium sulfate precipitation, agarose gel filtration and diethylaminoethylcellulose ion-exchange chromatography. Purified filamin is an asymmetric oligomer consisting of 2 large subunits of identical size (2 .times. 250,000 daltons) as indicated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, chemical cross-linking, sedimentation analysis (s20,w0 = 10 S) and Stokes'' radius estimation (a = 120 .ANG.). It had no intersubunit disulfide but appeared from oxidation studies to have adjacent thiols near the subunit interface. Filamin contained no amino sugars, methylated lysine, methylated histidine or hydroxyproline, nor did it exhibit myosin-like ATPase activities. Its amino acid composition and physical properties differed from those of gizzard myosin, for which a purification procedure was described. Filamin and the protein spectrin of erythrocyte membranes had strikingly similar physical properties, but they were chemically distinct.