Role of the lever arm in the processive stepping of myosin V.

Abstract

Myosin V is a two-headed molecular motor that binds six light chains per heavy chain, which creates unusually long lever arms. This motor moves processively along its actin track in discrete 36-nm steps. Our model is that one head of the two-headed myosin V tightly binds to actin and swings its long lever arm through a large angle, providing a stroke. We created single-headed constructs with different-size lever arms and show that stroke size is proportional to lever arm length. In a two-headed molecule, the stroke provides the directional bias, after which the unbound head diffuses to find its binding site, 36 nm forward. Our two-headed construct with all six light chains per head reconstitutes the 36-nm processive step seen in tissue-purified myosin V. Two-headed myosin V molecules with only four light chains per head are still processive, but their step size is reduced to 24 nm. A further reduction in the length of the lever arms to one light chain per head results in a motor that is unable to walk processively. This motor produces single small approximately 6-nm strokes, and ATPase and pyrene actin quench measurements show that only one of the heads of this dimer rapidly binds to actin for a given binding event. These data show that for myosin V with its normal proximal tail domain, both heads and a long lever arm are required for large, processive steps.

• Authors: Thomas J Purcell, Carl Morris, James A Spudich, H Lee Sweeney
• Journal: Proceedings of the National Academy of Sciences of the United States of America (Proc Natl Acad Sci U S A) Vol. 99 Issue 22 Pg. 14159-64 (Oct 29 2002) ISSN: 0027-8424 [Print] United States
• PMID: 12386339 (Publication Type: Journal Article, Research Support, U.S. Gov't, P.H.S.)

Chemical References

• Actins
• Pyrenes
• Recombinant Fusion Proteins
• Adenosine Triphosphatases
• Myosin Type V

Topics

• Actins (chemistry, metabolism)
• Adenosine Triphosphatases (chemistry, metabolism)
• Amino Acid Sequence
• Animals
• Chickens
• Models, Molecular
• Molecular Sequence Data
• Myosin Type V (chemistry, genetics, metabolism)
• Protein Processing, Post-Translational
• Protein Structure, Tertiary
• Pyrenes (chemistry, metabolism)
• Recombinant Fusion Proteins (chemistry, genetics, metabolism)