Protein Diffusion in the Membrane

At physiological temperatures, a lipid bilayer acts as a two-dimensional fluid that allows the diffusion of proteins, lipids, and other membrane components.

Lateral protein diffusion is sideways movement inside the membrane.

The extracellular matrix can interact with a protein's extracellular domain and interfere with its movement, or intracellularly, the actin cytoskeleton and the associated transmembrane proteins can form fences resulting in the creation of specific compartments known as corrals.

These cytoskeletal fences obstruct the free movement of proteins from one corral to another. However, actin turnover can create temporary gaps in the fence that can allow the proteins to move from one corral to another.

The lateral diffusion rate of proteins can be determined by fluorescence recovery after photobleaching or FRAP. In this technique, integral membrane proteins are labeled with fluorescent probes.

When an immobilized cell is irradiated with a laser beam, the fluorescent probe becomes photobleached, resulting in a circular non-fluorescent area. The lost fluorescence gradually recovers as unbleached proteins diffuse to the bleached area.