Structure of the insect troponin complex

Isolated troponin-tropomyosin complex from Lethocerus indicus asynchronous flight muscle forms paracrystals on a positively charged lipid monolayer. S ingle particle analysis was carried out on individual complexes selected fr om electron micrographs of negatively stained paracrystals. By a combinatio n of correlation and classification techniques, different average projectio ns of the object were obtained. An initial three-dimensional model was calc ulated by determining the Euler angles for the different views using a comm on line approach. This starting model was then used as a reference for the further three-dimensional refinement of the model using the original data s et. The refined model of the troponin complex has a diameter of approximate ly 90 Angstrom and a volume corresponding with a molecular mass of about 12 0 kDa for the globular domain. The resolution of the reconstruction was det ermined to be 32 Angstrom using the differential phase residual method and 26 Angstrom using the Fourier shell correlation criterion. (C) 1999 Academi c Press.