IDENTIFICATION OF HEMOGLOBIN DEGRADATION PRODUCTS IN PLASMODIUM-FALCIPARUM

Malaria parasites break down human hemoglobin to its constituent amino acids by cysteine and aspartic proteinases. However, no one has previ ously been able to identify hemoglobin cleavage products in intact par asites. When isolated parasites were subjected to non-denaturing polya crylamide gels electrophoresis, a unique protein band was found which contains heme and reacts with anti-human hemoglobin antibodies. This p rotein does not appear to represent oxidized or glycosylated hemoglobi n, and is present in isolated parasites but not in the cytosol of infe cted or uninfected erythrocytes. When this band was eluted and subject ed to SDS polyacrylamide gel electrophoresis, three bands were seen on Western blots. The proteins in these bands contain proteins with the N-terminal sequences of alpha- and beta-globin chains but molecular ma sses of only 13.2-13.4 kDa. These data suggest that hemoglobin alpha- and beta-chains are initially cleaved within the parasite phagolysosom e to release peptides of 15-17 and 23-25 amino acids from the C-termin i of alpha- and beta-globin chains, respectively. Production of the he moglobin breakdown products was inhibited by E-64, a cysteine proteina se inhibitor, suggesting the involvement of a cysteine proteinase in a n early step of hemoglobin degradation. (C) 1997 Elsevier Science B.V.