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Structural mosaicism on the submicron scale in the plasma membrane
1Department of Cell Biology and Anatomy, University of North Carolina, Chapel Hill 27599, USA.
Biophysical Journal
|February 4, 1998
Summary
Single particle tracking reveals neural cell adhesion molecule (NCAM) lateral mobility in cell membranes. NCAM exhibits varied diffusion patterns, including confinement, challenging existing models and suggesting a mosaic membrane structure.
Area of Science:
- Cell Biology
- Biophysics
- Neuroscience
Background:
- Neural cell adhesion molecule (NCAM) plays crucial roles in cell-cell interactions and signaling.
- Understanding the lateral mobility of NCAM is key to elucidating its function in dynamic cellular processes.
- Existing models, like the membrane skeleton fence model, propose specific constraints on protein diffusion.
Purpose of the Study:
- To investigate the lateral mobility of various neural cell adhesion molecule (NCAM) isoforms.
- To characterize diffusion dynamics of NCAM in different cellular environments (NIH 3T3 and C2C12 cells).
- To compare the mobility of transmembrane and glycosylphosphatidylinositol (GPI)-anchored NCAM isoforms.
Main Methods:
- Single particle tracking (SPT) was employed to monitor the movement of individual NCAM molecules.
- Different NCAM isoforms with varying ectodomains, anchorage modes, and cytoplasmic domains were expressed in cell lines.
- Diffusion patterns were analyzed over different time scales (6.6 s and 90 s) to capture transient and long-term behaviors.
Main Results:
- NCAM exhibited diverse mobility patterns, including Brownian diffusion, slow diffusion, corralled diffusion, and immobility.
- A significant fraction of NCAM showed mobile behavior, while a smaller portion experienced slow diffusion or transient confinement (approx. 8 s within 300-nm regions).
- Both transmembrane and GPI-anchored NCAM isoforms, as well as endogenous NCAM, displayed similar confinement behaviors, challenging the strict fence model.
Conclusions:
- The cell membrane acts as a mosaic with regions allowing free diffusion and others imposing transient confinement on NCAM.
- The observed mobility patterns, including a large mobile fraction and similar confinement for different isoforms, suggest a revision of current membrane diffusion models.
- These findings provide new insights into the dynamic organization of the cell membrane and the functional implications of NCAM mobility.