W0064

SANS Reveals the Influence of Phosphorylation on the Structure of the Cardiac Troponin Complex. William T. Heller¹, Natosha L. Finley², Wen-Ji Dong³, Peter Timmins⁴, Herbert C. Cheung³, Paul R. Rosevear², and Jill Trewhella⁵, ¹Center for Structural Molecular Biology and Condensed Matter Sciences Div., Oak Ridge National Laboratory, Oak Ridge, TN 37831; ²Dept. of Molecular Genetics, Biochemistry and Microbiology, Univ. of Cincinnati, College of Medicine, Cincinnati OH 45267; ³Dept. of Biochemistry and Molecular Genetics, Univ. of Alabama at Birmingham, Birmingham, AL 35294; ⁴Large Scale Structures Group, Institut Laue-Langevin, Avenue des Martyrs, BP 156 F-38042, Grenoble Cedex 9 France; ⁵Bioscience Div., Los Alamos National Laboratory, Los Alamos NM 87545.

Small-angle neutron scattering (SANS) with contrast variation has been used to determine the shapes and dispositions of the three subunits within the ternary cardiac troponin complex cTnC/cTnI/cTnT(198-298) and to study the influence of phosphorylation of cTnI on the solution structure. Contrast variation series data were collected for three different isotopically labeled variants of the cTnC/cTnI/cTnT(198-298) complex, one of which contained deuterated and bisphosphorylated cTnI. Analysis of the data shows that cTnT(198-298) interacts with one lobe of a somewhat compacted cTnC that sits at one end of an elongated rod-like cTnI, covering about one third of its length. The cTnT(198-298) sits near the center of the long cTnI axis. The cTnI subunit undergoes a significant conformational change in response to protein kinase A phosphorylation that results in reorientation of the other subunits within the complex. The rod-like cTnI bends sharply at the end interacting with cTnC/cTnT(198-298) component, which undergoes only a small structural change, reorients so as to maintain its contacts with cTnI.