Proteolytic digestion of band 3 at an external site alters the erythrocyte membrane organisation and may facilitate malarial invasion

Abstract

Invasion of human erythrocytes by Plasmodium falciparum is inhibited by chymostatin. This suggests that digestion of erythrocyte surface proteins by a protease with chymotrypsin-like activity may be involved in the invasion process. We find that treatment of intact erythrocytes with chymotrypsin cleaves the integral membrane protein, band 3, generating a major fragment with an apparent molecular weight of 58 kDa. We have used measurements of the rotational mobility of band 3, labelled with the phosphorescence probe, eosin-5-maleimide, as a monitor of the changes in the molecular organisation of the erythrocyte membrane which accompany band 3 cleavage. We report that the chymotrypsin treatment increases the rotational freedom of band 3, possibly due to conformational changes which disrupt its interaction with the underlying peripheral membrane proteins. We also show that chymotrypsin-treated erythrocytes undergo extensive endocytosis upon incorporation of exogenous fluorescently labelled phospholipid. We suggest that during the invasion process, digestion of band 3 by a chymotrypsin-like protease may induce a localised disruption of the erythrocyte membrane. This destabilised region of membrane may represent the site for the insertion of parasite-derived phospholipid, thus allowing the formation of the parasitophorous vacuole membrane.