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Dissecting Mechanoenzymatic Properties of Processive Myosins with Ultrafast Force-Clamp Spectroscopy
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Dissecting Mechanoenzymatic Properties of Processive Myosins with Ultrafast Force-Clamp Spectroscopy

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More than just a cargo adapter, melanophilin prolongs and slows processive runs of myosin Va

Maria Sckolnick1, Elena B Krementsova, David M Warshaw

  • 1From the Department of Molecular Physiology and Biophysics, University of Vermont, Burlington, Vermont 05405.

The Journal of Biological Chemistry
|August 28, 2013
PubMed

Insights

Melanophilin (Mlph) enhances melanosome transport by increasing the number of myosin Va (myoVa) motors on actin tracks. This adapter protein slows motor speed but increases run length, optimizing pigment organelle transfer.

Area of Science:

  • Cell Biology
  • Molecular Motors
  • Biophysics

Background:

  • Myosin Va (myoVa) is a molecular motor responsible for processive cargo transport along actin filaments.
  • Melanosomes, pigment organelles, are transported by kinesin and subsequently by myoVa in melanocytes.
  • Melanophilin (Mlph) acts as an adapter protein, linking Rab27a-melanosomes to myoVa.

Purpose of the Study:

  • To investigate the single-molecule behavior of myoVa when interacting with the adapter protein Mlph.
  • To elucidate how Mlph binding affects the processivity, speed, and run length of myoVa.
  • To understand the molecular mechanism by which Mlph modulates myoVa function for melanosome transport.

Main Methods:

  • Utilized total internal reflection fluorescence microscopy (TIRFm).
  • Employed quantum dot-labeled full-length myoVa for single-molecule visualization.
  • Analyzed motor stepping patterns and movement parameters.

Main Results:

  • Mlph increased the number of processively moving myoVa motors by 17-fold.
  • The myoVa-Mlph complex moved approximately 4-fold slower than myoVa alone but had double the run length.
  • Mlph binding induced a normal gating pattern in myoVa, suggesting cargo-dependent activation.
  • A positively charged cluster in Mlph's actin-binding domain was identified as crucial for these motor modifications.

Conclusions:

  • Mlph acts as a tether, modifying myoVa's motor properties to enhance melanosome transport efficiency.
  • The slower speed and longer run length of the myoVa-Mlph complex optimize melanosome transfer to keratinocytes.
  • Adapter proteins can fundamentally alter molecular motor behavior to fulfill specific biological roles.
Keywords:
GatingIntracellular TraffickingMelanophilinMyosinNanotechnologyProcessivityProtein DynamicsRegulationSlac-2aTethering

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