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Tropomodulin: a cytoskeletal protein that binds to the end of erythrocyte tropomyosin and inhibits tropomyosin binding to actin.
| Content Provider | Scilit |
|---|---|
| Author | Fowler, V. M. |
| Copyright Year | 1990 |
| Description | Journal: Journal of Cell Biology Human erythrocytes contain a Mr 43,000 tropomyosin-binding protein that is unrelated to actin and that has been proposed to play a role in modulating the association of tropomyosin with spectrin-actin complexes based on its stoichiometry in the membrane skeleton of one Mr 43,000 monomer per short actin filament (Fowler, V. M. 1987. J. Biol. Chem. 262:12792-12800). Here, we describe an improved procedure to purify milligram quantities to 98% homogeneity and we show that this protein inhibits tropomyosin binding to actin by a novel mechanism. We have named this protein tropomodulin. Unlike other proteins that inhibit tropomyosin-actin interactions, tropomodulin itself does not bind to F-actin. EM of rotary-shadowed tropomodulin-tropomyosin complexes reveal that tropomodulin (14.5 +/- 2.4 nm [SD] in diameter) binds to one of the ends of the rod-like tropomyosin molecules (33 nm long). In agreement with this observation, Dixon plots of inhibition curves demonstrate that tropomodulin is a non-competitive inhibitor of tropomyosin binding to F-actin (Ki = 0.7 microM). Hill plots of the binding of the tropomodulin-tropomyosin complex to actin indicate that binding does not exhibit any positive cooperativity (n = 0.9), in contrast to tropomyosin (n = 1.9), and that the apparent affinity of the complex for actin is reduced 20-fold with respect to that of tropomyosin. These results suggest that binding of tropomodulin to tropomyosin may block the ability of tropomyosin to self-associate in a head-to-tail fashion along the actin filament, thereby weakening its binding to actin. Antibodies to tropomodulin cross-react strongly with striated muscle troponin I (but not with troponin T) as well as with a nontroponin Mr 43,000 polypeptide in muscle and in other nonerythroid cells and tissues, including brain, lens, neutrophils, and endothelial cells. Thus, erythrocyte tropomodulin may be one member of a family of tropomyosin-binding proteins that function to regulate tropomyosin-actin interactions in non-muscle cells and tissues. |
| Related Links | http://jcb.rupress.org/content/jcb/111/2/471.full.pdf https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2116216/pdf http://jcb.rupress.org/content/111/2/471.full.pdf |
| ISSN | 00221295 |
| DOI | 10.1083/jcb.111.2.471 |
| Journal | Journal of Cell Biology |
| Issue Number | 2 |
| Volume Number | 111 |
| Language | English |
| Publisher | Rockefeller University Press |
| Publisher Date | 1990-08-01 |
| Access Restriction | Open |
| Subject Keyword | Journal: Journal of Cell Biology Biochemistry and Molecular Biology Actin Filament Actin Interactions Tropomodulin Binding To Actin Tropomyosin Actin Tropomyosin Binding Proteins |
| Content Type | Text |
| Resource Type | Article |
| Subject | Physiology |
