Identification of key residues involved in fibril formation by the conserved N-terminal region of Plasmodium falciparum merozoite surface protein 2 (MSP2) |
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Authors: | Xiaodong Yang Christopher G Adda Christopher A MacRaild Andrew Low Xuecheng Zhang Weiguang Zeng David C Jackson Robin F Anders Raymond S Norton |
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Institution: | 1. The Walter & Eliza Hall Institute of Medical Research, 1G Royal Parade, Parkville 3052, Australia;2. Department of Biochemistry, La Trobe University, Bundoora, 3083, Australia;3. Department of Microbiology & Immunology, The University of Melbourne, Parkville 3010, Australia |
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Abstract: | Merozoite surface protein 2 (MSP2) from the human malaria parasite Plasmodium falciparum is expressed as a GPI-anchored protein on the merozoite surface. MSP2 is assumed to have a role in erythrocyte invasion and is a leading vaccine candidate. Recombinant MSP2 forms amyloid-like fibrils upon storage, as do peptides corresponding to sequences in the conserved N-terminal region, which constitutes the structural core of fibrils formed by full-length MSP2. We have investigated the roles of individual residues in fibril formation and local ordered structure in two peptides, a recombinant 25-residue peptide corresponding to the entire N-terminal domain of mature MSP2 and an 8-residue peptide from the central region of this domain (residues 8–15). Both peptides formed fibrils that were similar to amyloid-like fibrils formed by full-length MSP2. Phe11 and Ile12 have important roles both in stabilising local structure in these peptides and promoting fibril formation; the F11A and I12A mutants of MSP28–15 were essentially unstructured in solution and fibril formation at pH 7.4 and 4.7 was markedly retarded. The T10A mutant showed intermediate behaviour, having a less well defined structure than wild-type and slower fibril formation at pH 7.4. The mutation of Phe11 and Ile12 in MSP21–25 significantly retarded but did not abolish fibril formation, indicating that these residues also play a key role in fibril formation by the entire N-terminal conserved region. These mutations had little effect on the aggregation of full-length MSP2, however, suggesting that regions outside the conserved N-terminus have unanticipated importance for fibril formation in the full-length protein. |
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Keywords: | Malaria Fibril Amyloid Nuclear magnetic resonance Structure |
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