Lateral movements of membrane glycoproteins restricted by dynamic cytoplasmic barriers

Area of Science:

• Cell biology
• Biophysics
• Immunology

Background:

• Cell membranes exhibit lateral domain formation, influenced by barriers within or associated with the bilayer.
• Major histocompatibility complex (MHC) class 1 molecules, including transmembrane (H-2Db) and glycosylphosphatidylinositol (GPI)-anchored (Qa2) forms, are crucial for immune function and cell surface interactions.

Purpose of the Study:

• To investigate the nature and location of barriers restricting the lateral movement of MHC class 1 molecules on the cell surface.
• To quantify the barrier-free path length (BFP) for different types of MHC molecules and assess the effect of temperature on these barriers.

Main Methods:

• Utilizing laser optical tweezers to manipulate antibody-coated gold particles attached to MHC molecules (H-2Db and Qa2) on cell surfaces.
• Measuring the barrier-free path length (BFP) by tracking the distance molecules moved before encountering a barrier at different temperatures (23°C and 34°C).

Main Results:

• At room temperature (23°C), the BFPs for Qa2 and H-2Db were 1.7 ± 0.2 and 0.6 ± 0.1 micrometers, respectively.
• Barriers remained present at 34°C, but the BFP for both MHC molecules increased approximately fivefold compared to 23°C.
• The temperature-dependent increase in BFP suggests barriers are dynamic and primarily located on the cytoplasmic side of the membrane.

Conclusions:

• Lateral movement of MHC class 1 molecules is restricted by dynamic barriers.
• These barriers are predominantly situated on the cytoplasmic face of the cell membrane.
• The findings provide insights into the structural organization and regulation of the cell membrane impacting protein mobility.