Question

1. We know (for example from fluorescence recovery after photobleaching 'FRAP' experiments) that the majority of cell membrane proteins diffuse laterally in the cell membrane. However, some transmembrane proteins might not readily diffuse laterally in the membrane. Either name a known type of protein, or make up an example, of a type of transmembrane protein that might tend to not diffuse readily within the membrane. Describe why it might not diffuse.

Answer 1

Four ways of restricting the lateral mobility of specific plasma membrane proteins

(A) The proteins can self-assemble into large aggregates (as seen for bacteriorhodopsin in the purple membrane of Halobacterium);

(B) they can be tethered by interactions with assemblies of macromolecules outside

or (C) they can be tethered by interactions with assemblies of macromolecules inside the cell;

or (D) they can interact with proteins on the surface of another cell.

Bacteriorhodopsin is the transmembrane protein that does not tend to diffuse laterally because it can self-assemble into large aggregates.