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Syntaxin clusters and cholesterol affect the mobility of Syntaxin1a.

Alan W Weisgerber1, Zdeněk Otruba1, Michelle K Knowles1

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|January 15, 2024
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Syntaxin1a (Syx1a) clusters are crucial for exocytosis. This study reveals Syx1a molecules move more freely within these nanodomains, a mobility dependent on cholesterol and the N-terminal Habc domain for proper cell function.

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Area of Science:

  • Cell Biology
  • Neuroscience
  • Biophysics

Background:

  • Syntaxin1a (Syx1a) is vital for exocytosis in neuroendocrine cells.
  • Syx1a forms nanoscale domains on the plasma membrane, which are essential for vesicle docking but disintegrate during fusion.
  • The dynamic balance of Syx1a molecules within these nanodomains is not fully understood.

Purpose of the Study:

  • To elucidate the dynamics of Syx1a molecules relative to cluster position.
  • To understand how Syx1a clusters maintain their balance and how molecules move within them.
  • To investigate the role of the N-terminal Habc domain and cholesterol in Syx1a dynamics and exocytosis.

Main Methods:

  • Developed a labeling strategy to visualize bulk Syx1a clusters and track single Syx1a molecule trajectories simultaneously on PC12 cells.
  • Tracked single Syx1a molecule movement in relation to cluster positions.
  • Utilized simulations to model Syx1a dynamics within clusters.

Main Results:

  • Syx1a molecules exhibit mobility on the plasma membrane, with higher mobility at cluster centers and reduced mobility at cluster edges.
  • The N-terminal Habc domain and cholesterol are essential for this mobility and proper exocytosis.
  • Simulations support a model of Syx1a clusters maintained by a large cage, with high mobility within a smaller radius.
  • Cholesterol depletion significantly reduces Syx1a mobility within clusters.

Conclusions:

  • Syx1a cluster dynamics are influenced by molecular mobility, with specific roles for the N-terminal Habc domain and cholesterol.
  • A caged diffusion model explains the observed Syx1a dynamics within nanodomains.
  • Plasma membrane fluidity, particularly within Syx1a supramolecular clusters, is critical for exocytosis function.