The molecular basis of muscle force is a configurational change in the myosin head while attached to actin. Such a change could either be a conformational change within the head itself, or it may be an alteration in the binding angle made with actin. The energy for force production is known to come from ATP hydrolysis, but while the """"""""tilting cross-bridge"""""""" hypothesis remains attractive, it is still unproven. Moreover, recent structural data have suggested that the configuration of attached myosin heads may be similar in both the ATP and ADP-Pi states. One problem in testing the tilting bridge hypothesis has been the difficulty of establishing the structures of so-called weakly bound acto-myosin states that occur in the presence of ATP. A considerable amount is known about the structure of the strongly bound states that occur in ADP or no nucleotide. However, other bound states have been elusive either because they dissociate at the low protein concentrations required for moderate resolution microscopy of the acto-myosin head (S1) complex or they are present only transiently. The applicant recently found conditions that allow one to observe transient and weakly bound states and has been studying their structures by electron cryo-microscopy of hydrated specimens. The micrographs already obtained show a variety of attached S1 configurations during steady-state ATP hydrolysis; such data are therefore compatible with the tilting bridge hypothesis but do not prove it.

Agency
National Institute of Health (NIH)
Institute
National Institute of Biomedical Imaging and Bioengineering (NIBIB)
Type
Research Project (R01)
Project #
5R01EB000209-09
Application #
6654903
Study Section
Biophysical Chemistry Study Section (BBCB)
Program Officer
Korte, Brenda
Project Start
1995-04-01
Project End
2004-12-31
Budget Start
2003-09-01
Budget End
2004-12-31
Support Year
9
Fiscal Year
2003
Total Cost
$345,781
Indirect Cost
Name
Eastern Virginia Medical School
Department
Physiology
Type
Schools of Medicine
DUNS #
058625146
City
Norfolk
State
VA
Country
United States
Zip Code
23501
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White, Howard D; Ashcroft, Alison E (2007) Real-time measurement of myosin-nucleotide noncovalent complexes by electrospray ionization mass spectrometry. Biophys J 93:914-9

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