Vascular smooth muscle calponin. A novel troponin T-like protein.

Abstract

SUMMARY In a search for additional Ca 2+ regulatory components in vascular smooth muscle, a novel troponin T-like protein was purified from bovine aorta smooth muscle. The isolated protein was separated into several isoforms on isoelectric focusing. The major isoelectric variants were focused in the pH region of 8.4 to 9.1. The protein had slightly different molecular masses in the M r range of 35,000 on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Its molar ratio relative to tropomyosin in the muscle extract was estimated to be 0.9 = 1.0. The novel protein bound to the immobilized calmodulin and exhibited a number of common physicochemical properties with gizzard (Af r = 34,000) calmodulin-binding and F-actin-binding protein. The aorta and gizzard proteins were immunologically cross-reactive. Both proteins shared a common antigenic determinant with COOHterminal segments of rabbit skeletal and bovine cardiac troponin T and bound to the immobilized smooth muscle tropomyosin. Both proteins interacted with rabbit skeletal troponin C in the presence and absence of Ca 2 + , but they did not interact with troponin I. These results suggest that the novel protein, which is designated calponin, may be a specialized component of smooth muscle thin filament involved in the regulation of contractile apparatus. (Hypertension 11: 620-626, 1988) KEYWORDS • vascular smooth muscle • troponin T • tropomyosin • calmodulin-binding protein * calcium T HE contractile process of the muscle is regulated by changes in the sarcoplasmic Ca 2+ concentration. In cardiac and skeletal muscles, actin-myosin interaction is regulated by a specific actin-linked mechanism, the troponin-tropomyosin system.'" 3 Recent studies have suggested that the contraction of vascular smooth muscle is regulated by a Ca 2+ -dependent mechanism in addition to myosin light chain phosphorylation.4 "*The maintenance of vascular smooth muscle tone characterized by a prolonged force production with low energy cost (latch contraction) 7 " 9 could be a major contributor to peripheral vascular resistance. To understand potential myogenic factors responsible for the hypertensive state, the regulatory protein (or proteins) in the second Ca 2+ -dependent mechanism must be identified.We have reported novel proteins with M, values of 33,000 to 35,000 that are present in large amounts in a variety of vertebrate smooth muscles.

Mice lacking smooth muscle calponin display increased bone formation that is associated with enhancement of bone morphogenetic protein responses

“…The precise mechanism by which calponin negatively regulates BMP signalling remains to be elucidated. However, recent observations demonstrating physical and functional interactions between SMAD proteins and calmodulin (Zimmerman et al 1998) raise an interesting possibility that calponin, a calmodulin-binding protein (Takahashi et al 1986(Takahashi et al , 1988Wills et al 1993), might physically interact with SMAD proteins (Heldin et al 1997) or the calmodulin-SMAD complex and regulate the SMAD activity.…”

Properties of calponin isolated from sheep aorta thin filaments

“…Protein concentration was determined by the Lowry method based on molccular masses of 42 kOa for actin, 35 kDa for calponin [5] and 87 kDa for caldesmon [14]. ATPase activity was measured with an actomyosin made up of 0.5 mg/ml aorta actin and 0.125 mg/ml skeletal muscle myosin [15] in 50 or 90 mM KCI, l0 mM sodium azidc, 5 mM MgCb, I mM dithiothreitol.…”

“…c~-actinin, filamin) and those which are associated with the contractile actomyosin domain, such as caldesmon [1,2]. Calponin is a recently discovered actin binding protein, present in all smooth muscle cells, which can also bind tropomyosin, Ca ~' +, and Ca=+.calmodulin [3][4][5].…”

A role for serine-175 in modulating the molecular conformation of calponin

“…Calponin is a family of actin thin filament-associated proteins, first identified in smooth muscle [1,2] and later found also in nonmuscle cells [3,4]. Biochemical studies showed that calponin binds to actin [1,5,6], Ca# + -calmodulin [1,2], S100 protein [7], caltropin (calcyclin) [8], tropomyosin [2,9], myosin [10,11] and desmin [12,13].…”

“…Biochemical studies showed that calponin binds to actin [1,5,6], Ca# + -calmodulin [1,2], S100 protein [7], caltropin (calcyclin) [8], tropomyosin [2,9], myosin [10,11] and desmin [12,13]. Calponin's interactions with contractile and cytoskeletal proteins have led to its proposed role in modulating the Ca# + signalling of contractile and cytoskeletal functions in smooth muscle and non-muscle cells.…”