Intact Connecting Filaments Change Length in 2.3-nm Quanta

  • Felix Blyakhman
  • Anna Tourovskaya
  • Gerald H. Pollack
Part of the Advances in Experimental Medicine and Biology book series (AEMB, volume 481)


In isolated titin molecules, length changes may occur in discrete steps (Tskhovrebova et al., 1997; Rief et al., 1997). The extent to which such steps are preserved in the intact muscle-filament lattice has remained unclear. We carried out experiments on single isolated insect-flight-muscle myofibrils in which thin filaments had been functionally removed either by stretch beyond overlap or by a “rigor-stretch” protocol, leaving the connecting (titin) filaments as the sole length-absorbing agent. The myofibril was released or stretched by a motor in ramp-like fashion. The time course of length change in the single sarcomere was stepwise. The same was true for half-sarcomere lengths. The presence of steps at the sarcomere level implies that parallel filaments step synchronously, with high cooperativity. Step sizes showed a consistent distribution: The smallest size was ~2.3 nm, and others were integer multiples of that value. Similar results were found for stretch and release. To our knowledge, the ~2.3-nm step quantum is the smallest consistent biomechanical event ever demonstrated. This quantum is an order of magnitude smaller than anticipated from the folding/unfolding of a complete Ig- or fibronectin-like domain, and may imply that folding occurs in sub-domain increments. The 2.3-nm incremental length change corresponds to a single turn of the domains’ beta sheet.


Length Change Thin Filament Sarcomere Length Thick Filament Parallel Filament 
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Copyright information

© Springer Science+Business Media New York 2000

Authors and Affiliations

  • Felix Blyakhman
    • 2
  • Anna Tourovskaya
    • 1
  • Gerald H. Pollack
    • 1
  1. 1.Dept of BioengineeringUniversity of WashingtonSeattleUSA
  2. 2.Ural State UniversityEkaterinburgRussia

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