Apical membrane antigen 1 (AMA1) is expressed in schizont-stage malaria parasites and sporozoites and is thought to be involved in the invasion of host red blood cells. AMA1 is an important vaccine candidate, as immunization with this antigen induces a protective immune response in rodent and monkey models of human malaria. Additionally, anti-AMA1 polyclonal and monoclonal antibodies inhibit parasite invasion in vitro. We have isolated a 20-residue peptide (R1) from a random peptide library that binds to native AMA1 as expressed by Plasmodium falciparum parasites. Binding of R1 peptide is dependent on AMA1 having the proper conformation, is strain specific, and results in the inhibition of merozoite invasion of host erythrocytes. The solution structure of R1, as determined by nuclear magnetic resonance spectroscopy, contains two structured regions, both involving turns, but the first region, encompassing residues 5 to 10, is hydrophobic and the second, at residues 13 to 17, is more polar. Several lines of evidence reveal that R1 targets a "hot spot" on the AMA1 surface that is also recognized by other peptides and monoclonal antibodies that have previously been shown to inhibit merozoite invasion. The functional consequence of binding to this region by a variety of molecules is the inhibition of merozoite invasion into host erythrocytes. The interaction between these peptides and AMA1 may further our understanding of the molecular mechanisms of invasion by identifying critical functional regions of AMA1 and aid in the development of novel antimalarial strategies.

The structure of IP-10 was solved by NMR spectroscopy and represents the first structure from the class of agonists toward the receptor CXCR3. CXCR3 binding chemokines are unique in their ability to bind receptors from both the CC and CXC classes of chemokine receptors. An unusual structural feature of IP-10 was identified that may provide the basis for the ability of IP-10 to bind both CXCR3 and CCR3. The surface of IP-10 that interacts with the N-terminus of CXCR3 was defined by monitoring changes in the NMR spectrum of IP-10 upon addition of a CXCR3 N-terminal peptide. These studies indicated that the interaction involves a hydrophobic cleft, formed by the N-loop and 40s-loop region of IP-10, similar to the interaction surface observed for other chemokines such as IL-8. An additional region of interaction was observed that consists of a hydrophobic cleft formed by the N-terminus of IP-10 and 30s-loop of IP-10.

Type IV pilin monomers assemble to form fibers called pili that are required for a variety of bacterial functions. Pilin monomers oligomerize due to the interaction of part of their hydrophobic N-terminal ␣-helix. Engineering of a truncated pilin from Pseudomonas aeruginosa strain K122-4, where the first 28 residues are removed from the N terminus, yields a soluble, monomeric protein. This truncated pilin is shown to bind to its receptor and to decrease morbidity and mortality in mice upon administration 15 min before challenge with a heterologous strain of Pseudomonas. The structure of this truncated pilin reveals an ␣-helix at the N terminus that lies across a 4-stranded antiparallel ␤-sheet. A model for a pilus is proposed that takes into account both electrostatic and hydrophobic interactions of pilin subunits as well as previously published x-ray fiber diffraction data. Our model indicates that DNA or RNA cannot pass through the center of the pilus, however, the possibility exists for small organic molecules to pass through indicating a potential mechanism for signal transduction.

The opportunistic pathogen Pseudomonas aeruginosa produces multifunctional, polar, filamentous appendages termed type IV pili. Type IV pili are involved in colonization during infection, twitching motility, biofilm formation, bacteriophage infection, and natural transformation. Electrostatic surface analysis of modeled pilus fibers generated from P. aeruginosa strain PAK, K122-4, and KB-7 pilin monomers suggested that a solventexposed band of positive charge may be a common feature of all type IV pili. Several functions of type IV pili, including natural transformation and biofilm formation, involve DNA. We investigated the ability of P. aeruginosa type IV pili to bind DNA. Purified PAK, K122-4, and KB-7 pili were observed to bind both bacterial plasmid and salmon sperm DNA in a concentration-dependent and saturable manner. PAK pili had the highest affinity for DNA, followed by K122-4 and KB-7 pili. DNA binding involved backbone interactions and preferential binding to pyrimidine residues even though there was no evidence of sequence-specific binding. Pilusmediated DNA binding was a function of the intact pilus and thus required elements present in the quaternary structure. However, binding also involved the pilus tip as tip-specific, but not base-specific, antibodies inhibited DNA binding. The conservation of a Thr residue in all type IV pilin monomers examined to date, along with the electrostatic data, implies that DNA binding is a conserved function of type IV pili. Pilus-mediated DNA binding could be important for biofilm formation both in vivo during an infection and ex vivo on abiotic surfaces.