Solution Structure and Main Chain Dynamics of the Regulatory Domain (Residues 1–91) of Human Cardiac Troponin C

• Published in: The Journal of biological chemistry 1998-06, Vol.273 (25), p.15633-15638
• Main Authors: Pääkkönen, Kimmo, Annila, Arto, Sorsa, Tia, Pollesello, Piero, Tilgmann, Carola, Kilpeläinen, Ilkka, Karisola, Piia, Ulmanen, Ismo, Drakenberg, Torbjörn
• Format: Article
• Language: English
• Subjects: Amino Acid Sequence; Calcium - metabolism; Humans; Magnetic Resonance Spectroscopy; Models, Molecular; Molecular Sequence Data; Myocardium - chemistry; Protein Conformation; Solutions; Troponin C - chemistry
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.273.25.15633

The three-dimensional structure of calcium-loaded regulatory, i.e. N-terminal, domain (1–91) of human cardiac troponin C (cNTnC) was determined by NMR in water/trifluoroethanol (91:9 v/v) solution. The single-calcium-loaded cardiac regulatory domain is in a “closed” conformation with comparatively little exposed hydrophobic surface. Difference distance matrices computed from the families of Ca 2+ -cNTnC, the apo and two-calcium forms of the skeletal TnC (sNTnC) structures reveal similar relative orientations for the N, A, and D helices. The B and C helices are closer to the NAD framework in Ca 2+ -cNTnC and in apo-sNTnC than in 2·Ca 2+ -sNTnC. However, there is an indication of a conformational exchange based on broad 15 N resonances for several amino acids measured at several temperatures. A majority of the amides in the α-helices and in the calcium binding loop exhibit very fast motions with comparatively small amplitudes according to the Lipari-Szabo model. A few residues at the N and C termini are flexible. Data were recorded from nonlabeled and 15 N-labeled samples, and backbone dynamics was investigated by 15 N T 1 , T 2 , and heteronuclear nuclear Overhauser effect as well as by relaxation interference measurements.