PROTEOLYTIC DIGESTION OF BAND-3 AT AN EXTERNAL SITE ALTERS THE ERYTHROCYTE-MEMBRANE ORGANIZATION AND MAY FACILITATE MALARIAL INVASION

Invasion of human erythrocytes by Plasmodium falciparum is inhibited b y chymostatin. This suggests that digestion of erythrocyte surface pro teins by a protease with chymotrypsin-like activity may be involved in the invasion process. We find that treatment of intact erythrocytes w ith chymotrypsin cleaves the integral membrane protein, band 3, genera ting 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 whi ch accompany band 3 cleavage. We report that the chymotrypsin treatmen t increases the rotational freedom of band 3, possibly due to conforma tional changes which disrupt its interaction with the underlying perip heral membrane proteins. We also show that chymotrypsin-treated erythr ocytes undergo extensive endocytosis upon incorporation of exogenous f luorescently labelled phospholipid. We suggest that during the invasio n process, digestion of band 3 by a chymotrypsin-like protease may ind uce a localised disruption of the erythrocyte membrane. This destabili sed region of membrane may represent the site for the insertion of par asite-derived phospholipid, thus allowing the formation of the parasit ophorous vacuole membrane.