Molecular polarity in tropomyosin-troponin T co-crystals.
New features of the structure and interactions of troponin T and tropomyosin have been revealed by electron microscopy of so-called double-diamond co-crystals. These co-crystals were formed using rabbit alpha2 tropomyosin complexed with troponin T from either skeletal or cardiac muscle, which have different lengths in the amino-terminal region, as well as a bacterially expressed skeletal muscle troponin T fragment of 190 residues that lacks the amino-terminal region. Differences in the images of the co-crystals have allowed us to establish the polarities of both the troponin T subunit and tropomyosin in the projected lattice. Moreover, in agreement with their sequences, the amino-terminal region of a bovine cardiac muscle troponin T isoform appears to be longer than that from the rabbit skeletal muscle troponin T isoform and to span more of the amino terminus of tropomyosin at the head-to-tail filament joints. Images of crystals tilted relative to the electron beam also reveal the supercoiling of the tropomyosin filaments in this lattice. Based on these results, a three-dimensional model of the double-diamond lattice has been constructed.
Cabral-Lilly
D
D
Rosenstiel Basic Medical Sciences Research Center, Brandeis University, Waltham, Massachusetts 02254-9110, USA.
Tobacman
L S
LS
Mehegan
J P
JP
Cohen
C
C
D000818:Animals; D001665:Binding Sites; D055592:Biophysical Phenomena; D001703:Biophysics; D002417:Cattle; D003460:Crystallization; D066298:In Vitro Techniques; D008854:Microscopy, Electron; D008958:Models, Molecular; D018482:Muscle, Skeletal / Q000737:chemistry; D009206:Myocardium / Q000737:chemistry; D011485:Protein Binding; D011487:Protein Conformation; D011817:Rabbits; D014335:Tropomyosin / Q000737:chemistry* / Q000648:ultrastructure; D014336:Troponin / Q000737:chemistry* / Q000648:ultrastructure; D020107:Troponin T
D014335:Tropomyosin; D014336:Troponin; D020107:Troponin T