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A long helix from the central region of smooth muscle caldesmon

1991; Elsevier BV; Volume: 266; Issue: 21 Linguagem: Inglês

10.1016/s0021-9258(18)92796-1

1083-351X

C.L. Wang, Joseph M. Chalovich, Philip Graceffa, R C Lu, K. Mabuchi, Walter F. Stafford,

Genetic Neurodegenerative Diseases

The central region of smooth muscle caldesmon is predicted to form a-helices on the basis of its primary structure.We have isolated a fragment (CT54) that contains this region.The hydrodynamic properties and the electron microscopic images suggest that CT54 is an elongated (35 nm), monomeric molecule.The circular dichroic spectrum yields an overall a-helical content of 55-58%.These results are consistent with the model that the middle portion of CT54 forms a long stretch of single-stranded a-helix.Such a structure, if it in fact exists, is thought to be stabilized by numerous salt bridges between charged residues at positions i and i+4.The structural characteristics of this fragment not only represent an unusual protein configuration but also provide information about the functional role of caldesmon in smooth muscle contraction.Both smooth muscle and non-muscle cells contain a major heat-stable, actin-binding protein, caldesmon (1, for reviews, see Refs. 2, 3).Although the exact physiological role of caldesmon remains uncertain, its inhibition of actomyosin-activated ATP hydrolysis in vitro (4-7), its ability to respond to changes of the calcium concentration via interactions with calmodulin (4-6), and its binding to myosin (8, 9) have prompted much speculation that this thin filament-associated protein may be involved in some auxiliary mechanism for regulation (10)(11)(12).On the basis of its predicted secondary structure (13,14) and recent electron microscopic images (15), the molecule of smooth muscle caldesmon can be roughly divided into three parts: the N-terminal portion (residues 1- 249),' the middle portion (residues 250-396), and the C-HL41411 (to C. L. A. W.), AR35216 (to J. M. C.), AR30917 (to P.