[Intramolecular dynamics of human erythrocyte membrane proteins upon modification of spectrin by tryptophan...

The slow (millisecond) protein internal dynamics of isolated human erythrocyte membranes in suspension without treatment, after deleting 95% of spectrin, after spectrin thermal denaturation upon acidification of medium in the pH range 6.0-4.0, and spectrin extracted in solution from membranes has been studied by room-temperature tryptophan phosphorescence. It has been established that integral proteins and spectrin differ in structural and dynamic state. Millisecond movements of structural elements of integral proteins are more restricted compared with those of spectrin. The removal of spectrin from the membrane led to an increase in slow fluctuations of integral protein structure. This indicates that spectrin participates in the control of the structural and dynamic state of erythrocyte membrane proteins. As medium was acidified in the pH range 6.0-4.0, the protein slow internal dynamics of membranes in native state decreased, which was explained by spectrin pH aggregation. After thermal denaturation of spectrin, no pH-induced increase of membrane protein structure rigidity was observed.