Abstract
Malarial merozoites invade erythrocytes; and as an essential step in this invasion process, the 42-kDa fragment of Plasmodium falciparum merozoite surface protein-1 (MSP142) is further cleaved to a 33-kDa N-terminal polypeptide (MSP133) and an 19-kDa C-terminal fragment (MSP119) in a secondary processing step. Suramin was shown to inhibit both merozoite invasion and MSP142 proteolytic cleavage. This polysulfonated naphthylurea bound directly to recombinant P. falciparum MSP142 (Kd = 0.2 microM) and to Plasmodium vivax MSP142 (Kd = 0.3 microM) as measured by fluorescence enhancement in the presence of the protein and by isothermal titration calorimetry. Suramin bound only slightly less tightly to the P. vivax MSP133 (Kd = 1.5 microM) secondary processing product (fluorescence measurements), but very weakly to MSP119 (Kd approximately 15 mM) (NMR measurements). Several residues in MSP119 were implicated in the interaction with suramin using NMR measurements. A series of symmetrical suramin analogues that differ in the number of aromatic rings and substitution patterns of the terminal naphthylamine groups was examined in invasion and processing assays. Two classes of analogue with either two or four bridging rings were found to be active in both assays, whereas two other classes without bridging rings were inactive. We propose that suramin and related compounds inhibit erythrocyte invasion by binding to MSP1 and by preventing its cleavage by the secondary processing protease. The results indicate that enzymatic events during invasion are suitable targets for drug development and validate the novel concept of an inhibitor binding to a macromolecular substrate to prevent its proteolysis by a protease.
Highlights
Malarial merozoites invade erythrocytes; and as an essential step in this invasion process, the 42-kDa fragment of Plasmodium falciparum merozoite surface protein-1 (MSP142) is further cleaved to a 33-kDa N-terminal polypeptide (MSP133) and an 19-kDa C-terminal fragment (MSP119) in a secondary processing step
The protein complex is released from the merozoite surface following secondary processing, which involves a single proteolytic cleavage within MSP142
Suramin Inhibits Erythrocyte Invasion by Merozoites and MSP1 Secondary Processing—Suramin inhibition of erythrocyte invasion was measured both by microscopic examination of cultures following staining with Giemsa reagent and by biosynthetic incorporation of [3H]hypoxanthine
Summary
47670 –47677, 2003 Printed in U.S.A. Suramin and Suramin Analogues Inhibit Merozoite Surface Protein-1 Secondary Processing and Erythrocyte Invasion by the Malaria Parasite Plasmodium falciparum*. We propose that suramin and related compounds inhibit erythrocyte invasion by binding to MSP1 and by preventing its cleavage by the secondary processing protease. The protein complex is released from the merozoite surface following secondary processing, which involves a single proteolytic cleavage within MSP142. We have chosen to examine suramin, a symmetrical hexasulfated naphthylurea, to explore its ability to bind to MSP1 and to inhibit invasion because it has been shown that this highly charged compound interferes with interaction of growth factors containing EGF domains with their receptors [7,8,9,10]. Some suramin analogues are shown to inhibit processing and invasion
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have