PHOTOAFFINITY-LABELING OF CHLOROQUINE-BINDING PROTEINS IN PLASMODIUM-FALCIPARUM

A photoreactive analog of chloroquine, N-(4-(4-diethylamino-1 -methylb utylamino) quinolin-6-yl)-4-azido-2-hydroxybenzamide (referred to as A SA-Q), has been synthesized and shown to mimic the action of chloroqui ne in possessing substantial antimalarial activity against a chloroqui ne-sensitive strain of Plasmodium falciparum. As for chloroquine, ASA- Q is less effective at killing drug-resistant strains of malaria, and the resistance can be modulated using the reagent verapamil. ASA-Q has been radiolabeled with (NaI)-I-125 and used as a photoaffinity probe for labeling chloroquine-binding proteins in malaria-infected erythroc ytes. Two proteins have been identified with apparent molecular masses of 42 and 33 kDa in both chloroquine-sensitive and chloroquine-resist ant strains of malaria. Photoaffinity labeling of the two proteins by iodo-ASA-Q and was competitively inhibited by an excess of unlabeled c hloroquine. The structurally related antimalarials amodiaquine and qui nine also inhibited labeling of the two proteins, while verapamil and doxycyclin had no effect. We suggest that the two labeled proteins are the macromolecular targets of chloroquine action in malaria parasites .