Lateral mobility of integral membrane proteins is increased in spherocytic erythrocytes

Abstract

Alterations of glycoprotein distribution and lateral mobility in cell membranes can provide transmembrane signals for several membrane-related phenomena^1–3. Control of the transmembranous events has been ascribed to interaction between submembranous protein matrices (or ‘cytoskeletons’) and membrane glycoproteins^4–7. A consequence of such interaction would be differential inhibition of protein lateral diffusion in biological membranes. Measurements of the lateral diffusion coefficients of membrane proteins, in fact, have generally yielded values^8–12 much less than were predicted for unhindered diffusion in a fluid bilayer^13,14. The mouse spherocytic erythrocyte, which lacks the major components of the normal erythrocyte membrane matrix¹⁵ (composed of spectrin, actin, bands 4.1 and 4.9 (ref. 16), in the nomenclature of Fairbanks et al.¹⁷), provides a unique system for a direct evaluation of the effect of the matrix on protein lateral mobility. After using a modification of the technique of fluorescence redistribution after photobleaching (FRAP)¹⁸, we report here that membrane proteins diffuse about 50 times faster in spherocytic than in normal mouse erythrocytes.