Tropomyosin

 First discovered by Bailey (Bailey, 1948), the tropomyosins are a group of proteins that bind to the sides of actin filaments and (together with troponins) regulate the interaction of the filaments with myosin in response to Ca2+. They are parallel, a-helical, coiled coil dimers. Vertebrates typically express in the region of 20 different tropomyosins from alternative spicing from about four tropomyosin genes (Perry, 2001 ). Tropomyosins exist as both homo-dimers and hetero-dimers held together by a series of salt bridges and hydrophobic interactions. They may also interact through their N and C termini in solution (especially in low ionic strength buffers) and this can be monitored by viscosity. There are two major groups of tropomyosin the high and low molecular weight tropomyosins. The former type exist primarily in muscle tissues (cardiac, smooth and skeletal) whereas non-muscle tissues express both high and low mol.wt. tropomyosins.