Identification and Characterization of Falcilysin, a Metallopeptidase Involved in Hemoglobin Catabolism within the Malaria Parasite Plasmodium falciparum

Abstract

The malaria parasite Plasmodium falciparum degrades hemoglobin in its acidic food vacuole for use as a major nutrient source. A novel metallopeptidase activity, falcilysin, was purified from food vacuoles and characterized. Falcilysin appears to function downstream of the aspartic proteases plasmepsins I and II and the cysteine protease falcipain in the hemoglobin proteolytic pathway. It is unable to cleave hemoglobin or denatured globin but readily destroys peptide fragments of hemoglobin. Falcilysin cleavage sites along the ␣ and ␤ chains of hemoglobin are polar in character, with charged residues located in the P1 and/or P4 positions. In contrast, plasmepsins I and II and falcipain prefer hydrophobic residues around the scissile bond. The gene encoding falcilysin has been cloned. Its coding sequence exhibits features characteristic of clan ME family M16 metallopeptidases, including an "inverted" HXXEH active site motif. Falcilysin shares primary structural features with M16 family members such as insulysin, mitochondrial processing peptidase, nardilysin, and pitrilysin as well as with data base hypothetical proteins that are potential M16 family members. The characterization of falcilysin increases our understanding of hemoglobin catabolism in P. falciparum and the unusual M16 family of metallopeptidases.

A Multi-enzyme Cascade of Hemoglobin Proteolysis in the Intestine of Blood-feeding Hookworms

“…P. falciparum also expresses vacuolar cysteine proteases, termed falcipains, which are able to digest native Hb and denatured globin (4 -6). After initial digestion with plasmepsins and falcipains, a P. falciparum metalloprotease, falcilysin, digests globin fragments even further (7).…”

A Plasmodium falciparum Dipeptidyl Aminopeptidase I Participates in Vacuolar Hemoglobin Degradation

“…Further degradation of the globin chains is achieved through the action of plasmepsins I, II, and IV (10 -12), histo-aspartic protease (11), and three cysteine proteases, falcipain-2, -2Ј, and -3 (13)(14)(15). The metalloprotease falcilysin converts short globin polypeptides into oligopeptides consisting of 5-10 amino acids (16). Inhibitors of both plasmepsins and falcipains block hemoglobin degradation and kill P. falciparum (5,17).…”

Plasmodium falciparum falcilysin: an unprocessed food vacuole enzyme

“…Plasmepsins, and a family of cysteine proteases, falcipain-2 and 3, then carry out further degradation of the denatured globin [2][3][4][5]. The resulting small globin peptides serve as substrates for falcilysin (FLN) [6].…”

“…Plasmepsins, and a family of cysteine proteases, falcipain-2 and 3, then carry out further degradation of the denatured globin [2][3][4][5]. The resulting small globin peptides serve as substrates for falcilysin (FLN) [6].FLN was first identified in 1999 when analysis of degraded globin fragments from the food vacuole revealed several peptides with cleavage sites that could not be attributed to the known proteases [7]. Specifically, a protease preferring to cleave substrates at polar or charged residues was implicated; this stands in contrast to the other hemoglobin-degrading proteases, which favor cleavage at hydrophobic residues.…”