Soteriou A, Clarke A, Martin S, Trinick J
Department of Veterinary Medicine, Bristol University, Langford, U.K.
Proc Biol Sci. 1993 Nov 22;254(1340):83-6. doi: 10.1098/rspb.1993.0130.
Molecules of the giant protein titin are responsible for the passive elasticity and central A-band location of muscle myofibrils. The molecular mechanism of titin elasticity is not known, but the I-band region of the molecule appears capable of approximately fourfold reversible extension. Such large extensions are likely to involve unfolding of titin domains. In the present experiments, equilibrium unfolding of titin from rabbit skeletal muscles was studied in vitro by fluorescence and circular dichroism spectroscopy, after addition of guanidinium chloride. The data suggest two unfolding transitions, both of which appear cooperative. The second transition is likely to involve complete unfolding of the immunoglobulin- and fibronectin-like domains from which the molecules is composed. The free energy associated with this transition is comparable with the energy required to extend titin molecules to the maximum amount seen in situ.
巨大的肌联蛋白分子负责肌肉肌原纤维的被动弹性和中央A带的定位。肌联蛋白弹性的分子机制尚不清楚，但该分子的I带区域似乎能够进行大约四倍的可逆伸展。如此大的伸展可能涉及肌联蛋白结构域的展开。在本实验中，在添加氯化胍后，通过荧光和圆二色光谱法在体外研究了兔骨骼肌中肌联蛋白的平衡展开。数据表明有两个展开转变，两者似乎都是协同的。第二个转变可能涉及构成该分子的免疫球蛋白样和纤连蛋白样结构域的完全展开。与该转变相关的自由能与将肌联蛋白分子伸展到原位所见最大量所需的能量相当。
