Open AccessCalcium‐dependent distance changes in binary and ternary complexes of troponin
Author(s) -
SCHULZKI HorstDieter,
KRAMER Bernd,
FLEISCHHAUER Jörg,
MERCOLA Daniel A.,
WOLLMER Axel
Publication year - 1990
Publication title -
european journal of biochemistry
Language(s) - English
Resource type - Journals
eISSN - 1432-1033
pISSN - 0014-2956
DOI - 10.1111/j.1432-1033.1990.tb15537.x
Subject(s) - biophysics , troponin c , ternary operation , calcium , chemistry , troponin , ternary complex , crystallography , myofilament , protein subunit , förster resonance energy transfer , myosin , troponin i , stereochemistry , biochemistry , biology , enzyme , fluorescence , physics , quantum mechanics , psychology , organic chemistry , psychiatry , myocardial infarction , computer science , gene , programming language
Calcium‐dependent distance changes have been determined by resonance energy transfer in binary and ternary troponin complexes in order to collect evidence for the structural rearrangements which are part of the hypothetical trigger mechanism of skeletal muscle contraction. Donor and acceptor fluorophores were either intrinisic tryptophans in subunits with a favourable sequence from different species, quasi‐intrinsic Tb 3+ ions bound to troponin C or extrinsic labels attached to specific cysteine or methionine residues. All chemically modified subunits proved fully active in conferring calcium sensitivity onto myosin ATPase. Nine distances were determined between five sites which allowed construction of a three‐dimensional lattice representing the spatial distribution of four sites in the ternary complex of troponin C, I and T. Distances in binary complexes were nearly unaltered upon addition of the third subunit. Regulatory calcium binding caused distance changes of the order of 0.7 – 1.1 nm. In view of the large displacements of the hypothetical mechanism, they turned out to be smaller than anticipated. The fluorophoric sites selected may be localized in a zone of the troponin complex which happens to be relatively little affected by the mechanism. Alternatively, amplification of the moderate changes seen here would require the complete set of thin filament proteins.