A model of stereocilia adaptation based on single molecule mechanical studies of myosin I

Philos Trans R Soc Lond B Biol Sci. 2004 Dec 29;359(1452):1895-905. doi: 10.1098/rstb.2004.1559.


We have used an optical tweezers-based apparatus to perform single molecule mechanical experiments using the unconventional myosins, Myo1b and Myo1c. The single-headed nature and slow ATPase kinetics of these myosins make them ideal for detailed studies of the molecular mechanism of force generation by acto-myosin. Myo1c exhibits several features that have not been seen using fast skeletal muscle myosin II. (i) The working stroke occurs in two, distinct phases, producing an initial 3 nm and then a further 1.5 nm of movement. (ii) Two types of binding interaction were observed: short-lived ATP-independent binding events that produced no movement and longer-lived, ATP-dependent events that produced a full working stroke. The stiffness of both types of interaction was similar. (iii) In a new type of experiment, using feedback to apply controlled displacements to a single acto-myosin cross-bridge, we found abrupt changes in force during attachment of the acto-Myo1b cross-bridge, a result that is consistent with the classical 'T2' behaviour of single muscle fibres. Given that these myosins might exhibit the classical T2 behaviour, we propose a new model to explain the slow phase of sensory adaptation of the hair cells of the inner ear.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Actins / metabolism
  • Actins / physiology*
  • Adaptation, Physiological*
  • Adenosine Triphosphate / metabolism
  • Animals
  • Biomechanical Phenomena
  • Hair Cells, Auditory / physiology*
  • Mechanotransduction, Cellular / physiology
  • Models, Biological*
  • Muscle Contraction / physiology*
  • Myosins / metabolism
  • Myosins / physiology*
  • Rats


  • Actins
  • Adenosine Triphosphate
  • Myosins