Structure of the insect troponin complex

Isolated troponin-tropomyosin complex from Lethocerus indicus asynchronous flight muscle forms paracrystals on a positively charged lipid monolayer. Single particle analysis was carried out on individual complexes selected from electron micrographs of negatively stained paracrystals. By a combination of correlation and classification techniques, different average projections of the object were obtained. An initial three-dimensional model was calculated by determining the Euler angles for the different views using a common line approach. This starting model was then used as a reference for the further three-dimensional refinement of the model using the original data set. The refined model of the troponin complex has a diameter of approximately 90 Angstrom and a volume corresponding with a molecular mass of about 120 kDa for the globular domain. The resolution of the reconstruction was determined to be 32 Angstrom using the differential phase residual method and 26 Angstrom using the Fourier shell correlation criterion. (C) 1999 Academic Press.