New drugs are needed to treat toxoplasmosis. Toxoplasma gondii calcium-dependent protein kinases (TgCDPKs) are attractive targets because they are absent in mammals. We show that TgCDPK1 is inhibited by low nanomolar levels of bumped kinase inhibitors (BKIs), compounds designed to be inactive against mammalian kinases. Cocrystal structures of TgCDPK1 with BKIs confirm that the structural basis for selectivity is due to the unique glycine gatekeeper residue in the ATP-binding site at residue 128. We show that BKIs interfere with an early step in T. gondii infection of human cells in culture. Furthermore, we show that TgCDPK1 is the in vivo target of BKIs because T. gondii cells expressing a glycine to methionine gatekeeper mutant enzyme show significantly decreased sensitivity to this class of selective kinase inhibitors. Thus, design of selective TgCDPK1 inhibitors with low host toxicity may be achievable.The food-borne apicomplexan protozoan Toxoplasma gondii is the causative agent of toxoplasmosis and may be the most common infectious eukaryotic parasite of humans, based Correspondence should be addressed to W.C.V.V. (wesley@u.washington.edu) or E.A.M. (merritt@u.washington.edu). Accession codes. Protein Data Bank: Atomic coordinates and structure factors have been deposited with accession numbers 3I79 (apo), 3I7c (NA-PP2 complex) and 3I7b (NM-PP1 complex).Note: Supplementary information is available on the Nature Structural & Molecular Biology website. AUTHOR CONTRIBUTIONSK.K.O., K.R.K., K.K.I. and W.C.V.V. were involved in the biochemical characterization and testing of inhibitors of TgCDPK1; L.J.C., K.K.O., K.R.K., A.J.N., C.L.M.J.V., F.S.B. and W.C.V.V. selected, cloned and purified the recombinant wild-type and mutant TgCDPK1 protein; E.T.L., J.E.K., T.L.A., L.Z., W.G.J.H. and E.A.M. crystallized and solved the structure of TgCDPK1; R.M. and D.J.M. synthesized the inhibitors; A.E.D. and M.P. performed the cellular T. gondii experiments; K.K.O., E.T.L., A.E.D., D.J.M., M.P., E.A.M. and W.C.V.V. wrote the paper; all authors reviewed and edited the paper. COMPETING FINANCIAL INTERESTSThe authors declare no competing financial interests.Reprints and permissions information is available online at http://npg.nature.com/reprintsandpermissions/. 10 . These drugs are problematic in that they can cause rash, leucopenia and nephrotoxicity11, and sulfadiazine and pyrimethamine can result in complications during pregnancy. New therapeutics against T. gondii are needed. NIH Public AccessCalcium levels have long been associated with T. gondii's interrelated processes of invasion, gliding motility and secretion 12 . The intracellular Ca 2+ level oscillates during gliding motility and is promptly dampened upon cell invasion, preventing T. gondii from immediately gliding out of cells 13 . Calcium oscillations control many targets in the cell, and the mediation of invasion, micronemal secretion and gliding motility is thought to be largely due to T. gondii calcium-dependent protein kinases (TgCDPKs) 12,14 .Protein ...

The protozoans Cryptosporidium parvum and Toxoplasma gondii are parasites of major health concern to humans. Both parasites contain a group of calcium-dependent protein kinases (CDPKs), which are found in plants and ciliates but not in humans or fungi. Here we describe a series of potent inhibitors that target CDPK1 in C. parvum (CpCDPK1) and T. gondii (TgCDPK1). These inhibitors are highly selective for CpCDPK1 and TgCDPK1 over the mammalian kinases SRC and ABL. Furthermore, they are able to block an early stage of C. parvum invasion of HCT-8 host cells, which is similar to their effects on T. gondii invasion of human fibroblasts.

Archaea and their viruses are poorly understood when compared with the Eukarya and Bacteria domains of life. We report here the crystal structure of the major capsid protein (MCP) of the Sulfolobus turreted icosahedral virus, an archaeal virus isolated from an acidic hot spring (pH 2-4, 72-92°C) in Yellowstone National Park. The structure is nearly identical to the MCP structures of the eukaryotic Paramecium bursaria Chlorella virus, and the bacteriophage PRD1, and shows a common fold with the mammalian adenovirus. Structural analysis of the capsid architecture, determined by fitting the subunit into the electron cryomicroscopy reconstruction of the virus, identified a number of key interactions that are akin to those observed in adenovirus and PRD1. The similar capsid proteins and capsid architectures strongly suggest that these viral capsids originated and evolved from a common ancestor. Hence, this work provides a previously undescribed example of a viral relationship spanning the three domains of life (Eukarya, Bacteria, and Archaea). The MCP structure also provides insights into the stabilizing forces required for extracellular hyperthermophilic proteins to tolerate high-temperature hot springs.crystallography ͉ evolution ͉ hyperthermophile ͉ electron cryomicroscopy T he Sulfolobus turreted icosahedral virus (STIV) infects Sulfolobus solfataricus, an acidophilic hyperthermophilic organism (grows optimally at pH 2-4 and at Ͼ80°C) that is emerging as a model for studying hyperthermophilic archaea and their viruses (1). STIV possesses a 17,663-bp circular dsDNA genome that encodes 36 predicted ORFs (2). The viral particle is composed of a 37-kDa major capsid protein (MCP) and several 25-, 12.5-, and 10-kDa minor capsid proteins (2). The electron cryomicroscopy (cryo-EM) image reconstruction of STIV showed a pseudo T ϭ 31 icosahedral capsid with trimers at the quasi sixfold coordinated positions, turret-like appendages at the vertices, and what appears to be an internal lipid membrane sandwiched between the genome and capsid shell (2). The capsid architecture of STIV is reminiscent of the mammalian adenovirus, bacteriophage PRD1, and Paramecium bursaria Chlorella virus (PBCV-1). The viral capsids of adenovirus, PRD1, and PBCV-1 are believed to have descended from a common ancestor (3). By using sequence alignment and modeling techniques, this lineage was recently extended to include additional large-faceted viruses containing a double-barrel trimeric major coat protein (4).Here we report the crystal structure of the STIV MCP and show its structural homology and sequence similarity to the MCPs of the adenovirus, PRD1, and PBCV-1. We further analyze the capsid architecture of STIV by docking the MCP crystal structure into the cryo-EM reconstruction and calculating a difference map. Our analysis reveals a number of quaternary interactions similar to those observed in adenovirus and PRD1. The structural and sequence comparison between the MCPs of these viruses, and similarities between their capsid architectures su...