To determine amino acid sequences of the Plasmodium falciparum MSP-1 protein that interact with red blood cell membranes in a specific receptor-ligand interaction, 78 sequential peptides, 20 amino acids long and spanning the entire length of the molecule, were synthesized and analysed with a specific binding assay developed for this purpose. Results show that peptides based on conserved and dimorphic regions of MSP-1, interact with human red blood cells (RBCs). This interaction occurs predominantly with peptides contained within the MSP-1 proteolytic fragments of 83 kDa, 38 kDa, 33 kDa and 19 kDa. Affinity constants of these peptides were between 140 and 250 nM. Peptide-RBC binding post enzyme treatment showed that the RBC receptors are not sialic acid dependent and appear to be proteic in nature. Some of these peptides inhibited merozoite invasion of RBCs yet did not inhibit intraerthrocytic development. These peptides, in conjunction with those from other merozoite surface proteins, may be used to rationally design a second generation of synthetic peptide-based malaria vaccines.

Biochemistry Z 0250 Intimate Molecular Interactions of P. falciparum Merozoite Proteins Involved in Invasion of Red Blood Cells and Their Implications for Vaccine Design -[443 refs.]. -(RODRIGUEZ, L. E.; CURTIDOR, H.; URQUIZA, M.; CIFUENTES, G.; REYES, C.; PATARROYO*, M. E.; Chem. Rev. (Washington, D. C.) 108 (2008) 9, 3656-3705; Inst. Immunol., Univ. Nac. Colombia, Bogota, Colombia; Eng.) -Lindner 50-274

Solid experimental evidence indicates that EBA-175 is used as a ligand by the Plasmodium falciparum merozoite to bind to human RBC, via different binding processing fragments. Using synthetic peptides and specific receptor-ligand interaction methodology, we have identified 6 high-activity binding sequences from the EBA-175 CAMP strain; peptide 1758 (KSYGTPDNIDKNMSLIHKHN), located in the so-called region I for which no binding activity has been reported before, peptides 1779 (NIDRIYDKNLLMIKEHILAI) and 1783 (HRNKKNDKLYRDEWWKVIKK), located in region II, in a sub-region known as 5' Cys F2, previously reported as being a binding region, and peptides 1814 (DRNSNTLHLKDYRNEENERH), 1815 (YTNQNINISQERDLQKHGFH) and 1818 (NNNFNNIPSRYNLYDKKLDL), in region III-V where antibodies inhibit merozoite invasion of erythrocytes. The affinity constants were between 60 and 180 nM and the critical amino acids involved in the binding were identified. The binding of these peptides to enzyme-treated RBC was analysed; binding of peptide 1814, located in the III-V region, was found to be sialic acid dependent. Some of these high binding peptides were able to inhibit in vitro merozoite invasion and to block the binding of recombinant RII-EBA to RBC. Several of these peptides are located in regions recognized by protective immune clusters of merozoites (ICMs) eluted antibodies.

in 1991. The principal focus of his research at the Fundación Instituto de Inmunología de Colombia is the molecular characterization of receptor-ligand interactions between pathogenic proteins involved in invasion and their corresponding host cell receptors, mainly for P. falciparum and M. tuberculosis. He is currently candidate for a Dr. Sc. degree in chemistry at the Universidad Nacional de Colombia.Mauricio Urquiza graduated in chemistry at the Universidad Nacional de Colombia in 1991. He is currently working as a researcher in the Virology department at the Fundación Instituto de Inmunología de Colombia and is candidate for a Dr. Sc. degree in chemistry at the Universidad Nacional de Colombia. The main focus of his research is the study of the host-parasite interactions, using as model P. falciparum, P. vivax, Human Papilloma virus, and Epstein-Barr virus. He is also working in the development of a Human Papilloma virus detection test.Gladys Cifuentes graduated in chemistry at the Universidad Nacional de Colombia in 1994 and is a member of the Nuclear Magnetic Resonance and Molecular Design section of the Three-Dimensional Structure Department at the Fundación Instituto de Inmunología de Colombia. Her research interests include 3D-structure and molecular design of peptides and proteins with shown biological and chemical relevance in host-parasite interactions.

MICALs (Molecule Interacting with CasL) are conserved multidomain enzymes essential for cytoskeletal reorganization in nerve development, endocytosis, and apoptosis. In these enzymes, a type-2 calponin homology (CH) domain always follows an N-terminal monooxygenase (MO) domain. Although the CH domain is required for MICAL-1 cellular localization and actin-associated function, its contribution to the modulation of MICAL activity towards actin remains unclear. Here, we present the structure of a fragment of MICAL-1 containing the MO and the CH domains—determined by X-ray crystallography and small angle scattering—as well as kinetics experiments designed to probe the contribution of the CH domain to the actin-modification activity. Our results suggest that the CH domain, which is loosely connected to the MO domain by a flexible linker and is far away from the catalytic site, couples F-actin to the enhancement of redox activity of MICALMO-CH by a cooperative mechanism involving a trans interaction between adjacently bound molecules. Binding cooperativity is also observed in other proteins regulating actin assembly/disassembly dynamics, such as ADF/Cofilins.