Aggregation of band 3 in hereditary ovalocytic red blood cell membranes. Electron microscopy and protein rotational diffusion studies

Abstract

Microaggregation of band 3 proteins in hereditary ovalocytic membranes was investigated by rotational diffusion measurements and by electron microscopy. It was previously shown that band 3 in ovalocytic membranes has decreased rotational mobility compared with band 3 in normal cells (Tilley, L., Nash, G.B., Jones, G.L. and Sawyer, W.L. (1991) J. Membr. Biol. 121, 59-66). This result could arise from either altered interactions with cytoskeletal proteins or from band 3 microaggregation. In the present study it was found that removal of spectrin and actin from the membrane had no effect on the rotational mobility of ovalocytic band 3. Additional removal of ankyrin and band 4.1, as well as cleavage of the cytoplasmic domain of band 3 with trypsin, did enhance band 3 mobility, as is the case in the membranes from normal cells. However, the rotational mobility of ovalocytic band 3 was always considerably less than that of normal band 3 under the same conditions. Scanning electron microscopy and low power electron micrographs of freeze-fracture replicas revealed that the surfaces of ovalocytes were more irregular than those of normal erythrocytes. At higher magnification, numerous linearly arranged intramembranous particles were observed on the P-faces of freeze-fractured ovalocytes but not on normal cells. These clusters consist of straight or slightly curved lines of 10-15 particles in single rows. From these results it is deduced that the reduced rotational mobility of band 3 in ovalocytes is a consequence of the formation of microaggregates, which are very probably induced by the mutation in the membrane-bound domain of ovalocytic band 3.