Hemoglobin degradation in the human malaria pathogen Plasmodium falciparum: a catabolic pathway initiated by a specific aspartic protease.

Abstract

SummaryHemoglobin is an important nutrient source for intraerythrocytic malaria organisms. Its catabolism occurs in an acidic digestive vacuole . Our previous studies suggested that an aspartic protease plays a key role in the degradative process. We have now isolated this enzyme and defined its role in the hemoglobinolysic pathway. Laser desorption mass spectrometry was used to analyze the proteolytic action of the purified protease. The enzyme has a remarkably stringent specificity towards native hemoglobin, making a single cleavage between tx33Phe and 34Leu. This scission is in the hemoglobin hinge region, unraveling the molecule and exposing other sites for proteolysis. The protease is inhibited by pepstatin and has NH2-terminal homology to mammalian aspartic proteases . Isolated digestive vacuoles make a pepstatin-inhibitable cleavage identical to that of the purified enzyme. The pivotal role of this aspartic hemoglobinase in initiating hemoglobin degradation in the malaria parasite digestive vacuoles is demonstrated.

Non specific resistance against malaria pre-erythrocytic stages: involvement of acute phase proteins

“…The existence of pro teolytic activity in the erythrocytic stages of Plasmodium is well described in the literature (Shrevel et al, 1990). These malaria proteases are divided in two groups, one active in an acidic envi ronment and involved in haemoglobin degradation (Bailly etal, 1991;Dame et al, 1994;Goldberg et al, 1991;Rosenthal etal, 1989;Vander Jagt etal, 1986), the other active in schizonts and/or merozoites with a role in merozoite maturation or red blood cell invasion (Banyal et al, 1990;Braun-Breton et al, 1988;Lyon et al, 1986;Rosenthal et al, 1987). The latter could also be involved in the regulation of parasite development within the hepatocyte.…”

Expression and Characterisation of Plasmepsin I from Plasmodium falciparum

“…Kinetic parameters were determined at pH 4.4 from two readily cleaved synthetic peptide substrates based on 470 the a-globin cleavage sequence [3] ( Table 1). The K, values were similar for both enzymes and the values were directly comparable to those obtained previously for hydrolysis of equivalent peptides by a number of other aspartic proteinases from various vertebrate and fungal species [38].…”

“…Plasmepsin I (originally termed aspartic haemoglobinase) was first identified as a component of mature P julciparum food vacuoles [3]. It was postulated that by cleaving the Phe33* Leu34 bond in the a-globin chain of native haemoglobin, plasmepsin I initiated the process of haemoglobin degradation, thus rendering the tetrameric protein open to attack by other endoand exo-peptidases.…”

Plasmodium falciparum falcilysin: an unprocessed food vacuole enzyme

“…A semi-ordered pathway of proteases mediates this catabolism, which occurs in the acidic organelle called the food vacuole. The aspartic proteases, plasmepsins I and II, are proposed to be responsible for initial cleavage of hemoglobin in a conserved hinge region of the alpha chain [1,2]. Plasmepsins, and a family of cysteine proteases, falcipain-2 and 3, then carry out further degradation of the denatured globin [2][3][4][5].…”