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Myosin 18A coassembles with nonmuscle myosin 2 to form mixed bipolar filaments

Neil Billington1, Jordan R Beach2, Sarah M Heissler1

  • 1Laboratory of Molecular Physiology, National Heart, Lung, and Blood Institute, NIH, Bethesda, MD 20892-8015, USA.

Current Biology : CB
|March 11, 2015
PubMed

Insights

Class-18 myosin 18A (M18A) does not function as a motor protein. Instead, M18A coassembles with nonmuscle myosin 2 (NM2) into mixed bipolar filaments, potentially regulating NM2 functions.

Area of Science:

  • Molecular and Cell Biology
  • Protein Interactions
  • Cytoskeletal Dynamics

Background:

  • Class-18 myosins are structurally related to conventional class-2 nonmuscle myosins (NM2).
  • Purified head domains of myosin 18A (M18A) lack intrinsic motor activity, suggesting non-motor functions.
  • M18A possesses an unusually long coiled-coil domain, hinting at filament-forming capabilities.

Purpose of the Study:

  • To investigate the in vivo function and assembly properties of full-length mouse myosin 18A (M18A).
  • To determine if M18A can form bipolar filaments independently or in association with NM2.
  • To explore the potential regulatory role of M18A in NM2 filament organization and function.

Main Methods:

  • Expression and purification of full-length mouse M18A using the baculovirus/Sf9 system.
  • In vitro biochemical assays including cosedimentation and electron microscopy to analyze M18A and NM2 filament formation.
  • Live-cell super-resolution imaging and immunostaining to visualize M18A and NM2 colocalization within cellular filaments.

Main Results:

  • Full-length M18A did not form large bipolar filaments on its own but formed a distinct bipolar structure.
  • M18A coassembled with NM2 to form mixed bipolar filaments, confirmed by multiple biochemical and imaging techniques.
  • Super-resolution microscopy revealed colocalization of M18A and NM2 within individual filaments in living cells.

Conclusions:

  • Myosin 18A (M18A) functions as a non-motor protein that coassembles with nonmuscle myosin 2 (NM2).
  • M18A integrates into NM2 filaments, suggesting it modulates filament properties, localization, and interactions.
  • These findings have significant implications for understanding the diverse roles of NM2 in cellular processes and development.

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