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Infection and Immunity, January 2007, p. 61-73, Vol. 75, No. 1
0019-9567/07/$08.00+0     doi:10.1128/IAI.01041-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Mimotopes of Apical Membrane Antigen 1: Structures of Phage-Derived Peptides Recognized by the Inhibitory Monoclonal Antibody 4G2dc1 and Design of a More Active Analogue{triangledown} ,{ddagger}

Jennifer K. Sabo,1 David W. Keizer,1,{dagger} Zhi-Ping Feng,1 Joanne L. Casey,2,3 Kathy Parisi,2,3 Andrew M. Coley,2,3 Michael Foley,2,3 and Raymond S. Norton1*

The Walter and Eliza Hall Institute of Medical Research, 1G Royal Parade, Parkville, Victoria 3050, Australia,1 Department of Biochemistry, La Trobe University, Bundoora, Victoria 3083, Australia,2 Cooperative Research Centre for Diagnostics, Department of Biochemistry, La Trobe University, Bundoora, Victoria 3083, Australia3

Received 3 July 2006/ Returned for modification 4 August 2006/ Accepted 9 October 2006

Apical membrane antigen 1 (AMA1) of the malaria parasite Plasmodium falciparum is an integral membrane protein that plays a key role in merozoite invasion of host erythrocytes. A monoclonal antibody, 4G2dc1, recognizes correctly folded AMA1 and blocks merozoite invasion. Phage display was used to identify peptides that bind to 4G2dc1 and mimic an important epitope of AMA1. Three of the highest-affinity binders—J1, J3, and J7—were chosen for antigenicity and immunogenicity studies. J1 and J7 were found to be true antigen mimics since both peptides generated inhibitory antibodies in rabbits (J. L. Casey et al., Infect. Immun. 72:1126-1134, 2004). In the present study, the solution structures of all three mimotopes were investigated by nuclear magnetic resonance spectroscopy. J1 adopted a well-defined region of structure, which can be attributed in part to the interactions of Trp11 with surrounding residues. In contrast, J3 and J7 did not adopt an ordered conformation over the majority of residues, although they share a region of local structure across their consensus sequence. Since J1 was the most structured of the peptides, it provided a template for the design of a constrained analogue, J1cc, which shares a structure similar to that of J1 and has a disulfide-stabilized conformation around the Trp11 region. J1cc binds with greater affinity to 4G2dc1 than does J1. These peptide structures provide the foundation for a better understanding of the complex conformational nature of inhibitory epitopes on AMA1. With its greater conformational stability and higher affinity for AMA1, J1cc may be a better in vitro correlate of immunity than the peptides identified by phage display.

* Corresponding author. Mailing address: The Walter and Eliza Hall Institute of Medical Research, 1G Royal Parade, Parkville, Victoria 3050, Australia. Phone: 61 3 9345 2306. Fax: 61 3 9345 2686. E-mail: ray.norton{at}wehi.edu.au.

{triangledown} Published ahead of print on 23 October 2006.

Editor: W. A. Petri, Jr.

{ddagger} Supplemental material for this article may be found at http://iai.asm.org/.

{dagger} Present address: Bio21 Institute, University of Melbourne, Melbourne, Victoria 3010, Australia.

Infection and Immunity, January 2007, p. 61-73, Vol. 75, No. 1
0019-9567/07/$08.00+0     doi:10.1128/IAI.01041-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.



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