REPETITIVE TITIN EPITOPES WITH A 42 NM SPACING COINCIDE IN RELATIVE POSITION WITH KNOWN A-BAND STRIATIONS ALSO IDENTIFIED BY MAJOR MYOSIN-ASSOCIATED PROTEINS - AN IMMUNOELECTRON-MICROSCOPICAL STUDY ON MYOFIBRILS

  • 1 September 1989
    • journal article
    • research article
    • Vol. 94, 119-125
Abstract
A direct titin-thick filament interaction in certain regions of the A band is suggested by results using four new monoclonal antibodies specific for titin in immunoelectron microscopy. Antibodies T30, T31 and T32 identify quasi-repeats in the titin molecule characterized by a 42-43 nm repeat spacing. These stripes seem to coincide with striations established by others on negatively stained cryosections of the A band. Antibodies T30 and T32 recognize epitopes matching five or two of the seven striations per half sacromere known to harbor both the myosin-associated C-protein and an 86K (K = 103 mr) protein. Antibody T31 labels two stripes in the P zone, which correspond to the two positions where decoration is seen with 86K protein, but not with C-protein. The single titin epitope defined by antibody T33 is located 55 nm prior to the center of the M band. This position seems to coincide with the M7 striation defined by others on negatively stained A bands. The T33 epitope position proves that the titin molecule, which is known to be anchored at the Z line, also penetrates into the complex architecture of the M band. The titin epitopes described here enable us to begin to correlate known ultrastructural aspects of the interior part of the A band with the disposition of the titin molecule in the sarcomere. They raise the question of whether there is a regular interaction pattern between titin and the thick filaments. Because of the limit of resolutoin of immunoelectron microscopy, it remains to be seen whether the repetitive thin epitopes of the C and P zones coincide exactly with the position of the myosin-associated proteins or lie on a similar lattice, out of register with these proteins.