Troponin I encompasses an extended troponin C in the Ca(2+)-bound complex: a small-angle X-ray and neutron scattering study

• Published in: Biochemistry (Easton) Vol. 33; no. 27; pp. 8233 - 8239
• Main Authors: Olah, G A, Rokop, S E, Wang, C L, Blechner, S L, Trewhella, J
• Format: Journal Article
• Language: English
• Published: United States 12.07.1994
• Subjects: Calcium - metabolism; Chemical Phenomena; Chemistry, Physical; Deuterium; Muscles - chemistry; Neutrons; Protein Conformation; Scattering, Radiation; Troponin - chemistry; Troponin - metabolism; Troponin C; Troponin I; X-Rays
• ISSN: 0006-2960
• DOI: 10.1021/bi00193a009

We have studied the solution structure of skeletal muscle troponin C complexed with troponin I in the presence of calcium using small-angle X-ray and neutron scattering. 4Ca2+.troponin C in the complex has an extended dumbbell shape with a radius of gyration of 23.9 +/- 0.5 A and a maximum linear dimension of approximately 72 A, similar to the values obtained from the crystal structure coordinates of troponin C (Herzberg & James, 1985). Troponin I is even more extended than troponin C with a radius of gyration of 41 +/- 2 A and a maximum linear dimension of approximately 118 A. The centers-of-mass for each component of the complex are approximately coincident (< 10-A separation) as are their long axes, and the troponin I component encompasses the 4Ca2+.troponin C. These data provide new insights into the nature of the conformational arrangement of this important Ca(2+)-sensitive molecular switch.