The protozoan parasite Plasmodium causes malaria, with hundreds of millions of cases recorded annually. Protection against malaria infection can be conferred by antibodies against merozoite surface protein (MSP)-1, making it an attractive vaccine candidate. Here we present the structure of the C-terminal domains of MSP-1 (known as MSP-1 19 ) from Plasmodium knowlesi. The structure reveals two tightly packed epidermal growth factor-like domains oriented head to tail. In domain 1, the molecule displays a histidine binding site formed primarily by a highly conserved tryptophan. The protein carries a pronounced overall negative charge primarily due to the large number of acidic groups in domain 2. To map protein binding surfaces on MSP-1 19 , we have analyzed the crystal contacts in five different crystal environments, revealing that domain 1 is highly preferred in protein-protein interactions. A comparison of MSP-1 19 structures from P. knowlesi, P. cynomolgi, and P. falciparum shows that, although the overall protein folds are similar, the molecules show significant differences in charge distribution. We propose the histidine binding site in domain 1 as a target for inhibitors of protein binding to MSP-1, which might prevent invasion of the merozoite into red blood cells.

ATP synthesis from ADP, P i , and Mg 2؉ takes place in mitochondria on the catalytic F 1 unit (␣ 3 ␤ 3 ␥␦⑀) of the ATP synthase complex (F 0 F 1 ), a remarkable nanomachine that interconverts electrochemical and mechanical energy, producing the high energy terminal bond of ATP. In currently available structural models of F 1 , the P-loop (amino acid residues 156 GGAGVGKT 163 ) contributes to substrate binding at the ␤ subunit catalytic sites. Here, we report the first transition state-like structure of F 1 (ADP⅐V i ⅐Mg⅐F 1 ) from rat liver that was crystallized with the phosphate (P i ) analog vanadate (VO 4 3؊ or V i ). Compared with earlier "ground state" structures, this new F 1 structure reveals that the active site region has undergone significant remodeling. P-loop residue alanine 158 is located much closer to V i than it is to P i in a previous structural model. No significant movements of P-loop residues of the ␣ subunit were observed at its analogous but noncatalytic sites. Under physiological conditions, such active site remodeling involving the small hydrophobic alanine residue may promote ATP synthesis by lowering the local dielectric constant, thus facilitating the dehydration of ADP and P i . This new crystallographic study provides strong support for the catalytic mechanism of ATP synthesis deduced from earlier biochemical studies of liver The mammalian mitochondrial ATP synthase (F 0 F 1 ) is a large protein complex (Fig. 1A) located in the inner membrane, where it catalyzes ATP synthesis from ADP, P i , and Mg 2ϩ at the expense of an electrochemical gradient of protons generated by the electron transport chain (reviewed in Refs. 1 and 2). Excluding regulators, the mammalian ATP synthase consists of 15 subunit types (3, 4), of which five in the stoichiometric ratio ␣ 3 ␤ 3 ␥␦⑀ comprise the F 1 catalytic unit (5), an ATP hydrolysis-driven motor, whereas an additional 10 comprise F 0 . One part of F 0 , containing subunits a and c, is embedded in the inner membrane to form a proton-driven motor, whereas a second part composed of subunits b, oligomycin sensitivity conferring protein (OSCP), and F 6 forms a side stalk (4, 6, 7) or "stator" extending from the membrane-embedded segment to the top of F 1 (4,8).During ATP synthesis in intact mitochondria, it is strongly believed, based on three-dimensional structures of F 1 (9, 10) and single molecule technology applied to the simpler bacterial enzymes (11,12), that the proton-driven motor contained within F 0 drives the ATP hydrolysisdriven motor (i.e. F 1 ) in the reverse direction to make ATP (Fig. 1A). In addition, more recent studies show that in mitochondria, the entire "double motor" ATP synthase complex is itself in complex formation with the phosphate carrier and adenine nucleotide carrier, forming an ATP synthase-phosphate carrier-adenine nucleotide carrier supercomplex named the "ATP synthasome" (13,14).To fully understand how ATP synthases work, we must elucidate three different levels of mechanism (Fig. 1A), these being (a) the mechanism (el...

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