Journal of Biological Chemistry · 2009 · 29 citations · 28 references
Life SciencesBiochemistryMolecular BiologyEnzyme MechanismEnzymologyStructural BiologyCatalytic MechanismsEnzyme Active SitesEnzyme FunctionEnzyme StructureLigand BindingStructural EnzymologyActive Site CatalysisAmino Acid RecognitionCatalytic Site ArchitectureEnzyme Active Site ArchitectureEnzyme Catalytic MechanismLigand Recognition MotifsMolecular Recognition In EnzymesPlasmodium Falciparum
d-tyrosyl-tRNATyr deacylase (DTD) is an editing enzyme that removes d-amino acids from mischarged tRNAs. We describe an in-depth analysis of the malaria parasite Plasmodium falciparum DTD here. Our data provide structural insights into DTD complexes with adenosine and d-amino acids. Bound adenosine is proximal to the DTD catalysis site, and it represents the authentic terminal adenosine of charged tRNA. DTD-bound d-amino acids cluster at three different subsites within the overall active site pocket. These subsites, called transition, active, and exit subsites allow docking, re-orientation, chiral selection, catalysis, and exit of the free d-amino acid from DTD. Our studies reveal variable modes of d-amino acid recognition by DTDs, suggesting an inherent plasticity that can accommodate all d- amino acids. An in-depth analysis of native, ADP-bound, and d- amino acid-complexed DTD structures provide the first atomic snapshots of ligand recognition and subsequent catalysis by this enzyme family. We have mapped sites for the deacylation reaction and mark possible routes for entry and egress of all substrates and products. We have also performed structure-based inhibitor discovery and tested lead compounds against the malaria parasite P. falciparum using growth inhibition assays. Our studies provide a comprehensive structural basis for the catalytic mechanism of DTD enzymes and have implications for inhibition of this enzyme in P. falciparum as a route to inhibiting the parasite. d-tyrosyl-tRNATyr deacylase (DTD) is an editing enzyme that removes d-amino acids from mischarged tRNAs. We describe an in-depth analysis of the malaria parasite Plasmodium falciparum DTD here. Our data provide structural insights into DTD complexes with adenosine and d-amino acids. Bound adenosine is proximal to the DTD catalysis site, and it represents the authentic terminal adenosine of charged tRNA. DTD-bound d-amino acids cluster at three different subsites within the overall active site pocket. These subsites, called transition, active, and exit subsites allow docking, re-orientation, chiral selection, catalysis, and exit of the free d-amino acid from DTD. Our studies reveal variable modes of d-amino acid recognition by DTDs, suggesting an inherent plasticity that can accommodate all d- amino acids. An in-depth analysis of native, ADP-bound, and d- amino acid-complexed DTD structures provide the first atomic snapshots of ligand recognition and subsequent catalysis by this enzyme family. We have mapped sites for the deacylation reaction and mark possible routes for entry and egress of all substrates and products. We have also performed structure-based inhibitor discovery and tested lead compounds against the malaria parasite P. falciparum using growth inhibition assays. Our studies provide a comprehensive structural basis for the catalytic mechanism of DTD enzymes and have implications for inhibition of this enzyme in P. falciparum as a route to inhibiting the parasite. IntroductionAminoacyl-tRNA synthetases (aaRSs) transfer l-amino acids to their cognate tRNA and are essential in the protein translation process. However, at times aaRS enzymes can also attach d-amino acids to tRNA, and this mistake can be toxic to growing cells. Tyrosyl-tRNA synthetases from Escherichia coli and Bacillus subtilis (1.Calendar R. Berg P. Biochemistry. 1966; 5: 1681-1690Crossref PubMed Scopus (160) Google Scholar, 2.Calendar R. Berg P. Biochemistry. 1966; 5: 1690-1695Crossref PubMed Scopus (139) Google Scholar), tyrosyl-tRNA synthetases from Saccharomyces cerevisiae (3.Soutourina J. Blanquet S. Plateau P. J. Biol. Chem. 2000; 275: 11626-11630Abstract Full Text Full Text PDF PubMed Scopus (43) Google Scholar) and tryptophanyl/aspartyl-tRNA synthetases from S. cerevisiae (4.Soutourina J. Plateau P. Blanquet S. J. Biol. Chem. 2000; 275: 32535-32542Abstract Full Text Full Text PDF PubMed Scopus (109) Google Scholar) can transfer d-forms of their cognate amino acids onto relevant tRNAs. To avoid introduction of d-amino acids in the translation machinery, almost all cells have editing domains like d-tyrosyl-tRNATyr deacylase (DTD). 4The abbreviations used are: DTDd-tyrosyl-tRNATyr deacylasePfDTDP. falciparum DTDAaDTDA. aeolicus DTDEcDTDE. coli DTDHiDTDH. influenzae DTDHsDTDH. sapiens DTDA3Sseryl-3′-aminoadenosineA3Ytyrosyl-3′-aminoadenosineDAPI4′,6-diamidino-2-phenylindoleNTAnitrilotriacetic acidPEGpolyethylene glycolMES4-morpholineethanesulfonic acidPBSphosphate-buffered saliner.m.s.d.root mean-square deviation. This enzyme cleaves the bond between d-amino acids and tRNA (Fig. 1A) and is encoded by the dtd gene in E. coli (5.Soutourina J. Plateau P. Delort F. Peirotes A. Blanquet S. J. Biol. Chem. 1999; 274: 19109-19114Abstract Full Text Full Text PDF PubMed Scopus (58) Google Scholar) and by the dtd1 gene in S. cerevisiae (3.Soutourina J. Blanquet S. Plateau P. J. Biol. Chem. 2000; 275: 11626-11630Abstract Full Text Full Text PDF PubMed Scopus (43) Google Scholar). Homologs of dtd/dtd1 genes are found in many genomes (S. cerevisiae, Caenorhabditis elegans, mouse, human (5.Soutourina J. Plateau P. Delort F. Peirotes A. Blanquet S. J. Biol. Chem. 1999; 274: 19109-19114Abstract Full Text Full Text PDF PubMed Scopus (58) Google Scholar), but not in archaea (4.Soutourina J. Plateau P. Blanquet S. J. Biol. Chem. 2000; 275: 32535-32542Abstract Full Text Full Text PDF PubMed Scopus (109) Google Scholar). However, another dtd2 (previously named GEK1) gene homologous to dtd/dtd1 is found in archaea and plants (6.Wydau S. Ferri-Fioni M.L. Blanquet S. Plateau P. Nucleic Acids Res. 2007; 35: 930-938Crossref PubMed Scopus (17) Google Scholar, 7.Ferri-Fioni M.L. Fromant M. Bouin A.P. Aubard C. Lazennec C. Plateau P. Blanquet S. J. Biol. Chem. 2006; 281: 27575-27585Abstract Full Text Full Text PDF PubMed Scopus (24) Google Scholar). DTD enzymes exhibit broad specificity toward various d-amino acid-charged tRNAs (d-aa-tRNA) and are essentially inactive toward l-aa-tRNAs (2.Calendar R. Berg P. Biochemistry. 1966; 5: 1690-1695Crossref PubMed Scopus (139) Google Scholar). Human DTD, also called DUE-B, has a long C-terminal extension and seems to be involved in d-amino acid resistance by deacylating d-aa-tRNAs during tRNA export (8.Zheng G. Liu W. Gong Y. Yang H. Yin B. Zhu J. Xie Y. Peng X. Qiang B. Yuan J. Biochem. J. 2009; 417: 85-94Crossref PubMed Scopus (22) Google Scholar).Plasmodium parasites are causative agents of malaria, which affects >500 million people and claims ∼2 million lives annually (9.Snow R.W. Guerra C.A. Noor A.M. Myint H.Y. Hay S.I. Nature. 2005; 434: 214-217Crossref PubMed Scopus (2129) Google Scholar). In the Plasmodium falciparum genome, there are no sequence homologs for d-amino acid oxidase and d-Ser racemase, but a single copy of the dtd gene is present. PfDTD may therefore be responsible for detoxification of d-amino acids in this parasite. The molecular weight of PfDTD is ∼20 kDa, and the sequence identity between PfDTD and its human homolog (HsDUE-B) is ∼35%.Native DTD structures have been reported from Aquifex aeolicus (AaDTD: PDB code 2DBO), E. coli (EcDTD: PDB code 1JKE, Ref. 10.Ferri-Fioni M.L. Schmitt E. Soutourina J. Plateau P. Mechulam Y. Blanquet S. J. Biol. Chem. 2001; 276: 47285-47290Abstract Full Text Full Text PDF PubMed Scopus (50) Google Scholar), Haemophilus influenza (HiDTD: PDB code 1J7G, Ref. 11.Lim K. Tempczyk A. Bonander N. Toedt J. Howard A. Eisenstein E. Herzberg O. J. Biol. Chem. 2003; 278: 13496-13502Abstract Full Text Full Text PDF PubMed Scopus (22) Google Scholar), Homo sapiens (HsDTD: PDB code 2OKV, Ref. 12.Kemp M. Bae B. Yu J.P. Ghosh M. Leffak M. Nair S.K. J. Biol. Chem. 2007; 282: 10441-10448Abstract Full Text Full Text PDF PubMed Scopus (19) Google Scholar), and Leishmania major (LmDTD: PDB code 1TC5). A catalytic mechanism has also been proposed on the basis of mutagenesis and tRNA modeling onto DTDs (11.Lim K. Tempczyk A. Bonander N. Toedt J. Howard A. Eisenstein E. Herzberg O. J. Biol. Chem. 2003; 278: 13496-13502Abstract Full Text Full Text PDF PubMed Scopus (22) Google Scholar, 12.Kemp M. Bae B. Yu J.P. Ghosh M. Leffak M. Nair S.K. J. Biol. Chem. 2007; 282: 10441-10448Abstract Full Text Full Text PDF PubMed Scopus (19) Google Scholar). However, to date, there are no DTD-ligand complex structures known from any organism. Here, we report a whole set of crystal structures of DTD from P. falciparum complexed with adenosine and various d-amino acids. The crystal structures of native, ADP-bound, and d-amino acid-complexed PfDTDs provide key insights into the binding and recognition modes for various ligands. Based on the high resolution structures of PfDTD, we have also performed in silico inhibitor screening and present data for four compounds that inhibit parasite growth. We believe that our analysis not only provides a structural basis for the catalytic mechanism for this family of editing enzymes, but also highlights a possible new focus for the development of specific antimalarials.DISCUSSIONPfDTD was overexpressed in E. coli, and the recombinant purified protein was crystallized in three different crystal growth solutions. We determined PfDTD structure using iodide-SAD technique, and we subsequently solved three different PfDTD-ADP structures along with several PfDTD-d-amino acid complex structures. The PfDTD crystals belong to a triclinic unit cell with three dimers each in the asymmetric unit. This presented PfDTD-ligand structures with three independent atomic views of the dimers. Further, the ligand-soaked crystals diffracted to higher resolution than native crystals facilitating better quality atomic dissection of PfDTD-ligand complexes.High resolution PfDTD-ligand structures allowed us to map transition/movement of each of the chemical groups involved in the deacylation reaction, including those involving protein side chains, the adenine ring, and the ribose pucker. The bound adenine ring stacks with active site Phe-89 in PfDTD, and this binding marks the transition site B1 that participates in recognition of the 3′-end of charged tRNA. We show that PfDTD bound d-amino acids cluster at three different subsites, termed transition, active, and exit, around and near the active site Thr-90 residue, which initiates catalysis. Our PfDTD co-crystal structures provide glimpses of several reaction intermediates. An in-depth analysis of substrates, products, and water networks has therefore allowed us to make an elaboration of PfDTD active site into multiple spatial components. Previously, catalytic mechanisms for DTDs have been proposed based on modeling studies (11.Lim K. Tempczyk A. Bonander N. Toedt J. Howard A. Eisenstein E. Herzberg O. J. Biol. Chem. 2003; 278: 13496-13502Abstract Full Text Full Text PDF PubMed Scopus (22) Google Scholar, 12.Kemp M. Bae B. Yu J.P. Ghosh M. Leffak M. Nair S.K. J. Biol. Chem. 2007; 282: 10441-10448Abstract Full Text Full Text PDF PubMed Scopus (19) Google Scholar). Our experimental data on PfDTD substrate interactions support the proposed reaction schemes and provide the first structural basis for these mechanisms. We propose several sequential steps that eventually catalyze deacylation of d-aa-tRNAs by DTD. These steps are: (i) electrostatic interactions along with minor conformational changes in PfDTD facilitate docking of 3′-end of tRNA on to PfDTD, (ii) insertion of water W1 at the dimeric interface and side chain movements of Asn-147 and water W2 then create space between PfDTD monomers (Fig. 4). This is followed by tethering of tRNA terminal adenine to entry point/transition site B1 of the active site Phe-89. It also allows for entry of covalently bound d-amino acid into the amino acid transition subsite T1, (iii) because of these steps, the pre-bound waters in the active region escape, making way for authentic substrates to reposition themselves. For example, exit of the pre-bound waters (found in our PfDTD complexes) likely facilitate flipping of carbonyl groups belonging to residues 135/137 and also allow movement of Ser-87 (Fig. 9 and supplemental Fig. S3). These minor conformational adjustments structurally and spatially rebuild the PfDTD active site, (iv) the above structural alterations then translate into side chain movements of Tyr-116, Phe-137, Phe-89, and Gln-88. Also, crucially there is a 120° rotation of the active site Thr-90 side chain. These then trigger traversal of d- amino acid-charged tRNA from transition site B1 to B2. Subsequently, the d-amino acid is presented in the enantiomer selectivity pocket (subsite T2). The task of enantiomeric selectivity is then potentially done by the completely invariant, conformationally restrained, and biochemically implicated Met-141 (26.Dwivedi S. Kruparani S.P. Sankaranarayanan R. Nat. Struct. Mol. Biol. 2005; 12: 556-557Crossref PubMed Scopus (45) Google Scholar, 27.Hussain T. Kruparani S.P. Pal B. Dock-Bregeon A.C. Dwivedi S. Shekar M.R. Sureshbabu K. Sankaranarayanan R. EMBO J. 2006; 25: 4152-4162Crossref PubMed Scopus (59) Google Scholar). Once the amino acid chirality is acceptable, its carbonyl carbon is placed proximal to the catalytic Thr-90, (vi) in the subsequent catalytic step, side chain Oγ of Thr-90 attacks the d-amino acid carbonyl carbon (C′) in a nucleophilic manner and the deprotonated amino group of d-amino acid accepts the hydroxyl proton from Thr-90. Thus, the tetrahedral transition state is formed and cleavage of d-aa-tRNA ester bond can take place (Fig. 11). The uncharged tRNA can thus exit the active site whereas the d-amino acid remains bound to DTD enzyme, vii) in the last step, catalytic water Wa1 moves into the active site and attacks the ester bond between DTD and d-amino acid resulting in its cleavage. The cleaved free d-amino acid subsequently enters the exit subsite E, which we have annotated in PfDTD. These steps represent the catalytic cycle and therefore allow generation of free DTD, free tRNA, and free d-amino acid. In summary, we present direct experimental evidence for the presence of several subsites within DTD, which together enable docking, cleavage, and egress of the recognized d-amino acid, thus leaving uncharged tRNA for another round of the aminoacylation reaction. The co-crystal structures of five d-amino acids with PfDTD also reveal inherent plasticity in the d-amino acid recognition sites. The latter is significant, because PfDTD is required to accommodate and catalyze reactions despite considerable differences in shape, size, and charge of d-amino acids.Using structure-based in silico screening routines, we selected 40 compounds for testing in parasite growth inhibition assays. Out of these, four compounds showed significant inhibition of parasite growth and compound 2 (N,N′-bis(4-amino-2-methyl-6-quinolinyl)urea, Fig. 13B) showed more than 90% inhibition. Compound 2 was found to dock at B1 and B2 subsites of PfDTD active site pocket, where the terminal adenosine of d-amino acid charged tRNA docks during deacylation; this observation implies that compound 2 might be competing with PfDTD substrate. These data provide initial evidence that inhibitors like compound 2 may be useful as novel inhibitors against the malaria parasite given that only a single copy of dtd gene is present in the malaria genome. We also observed that higher concentrations of d-isoleucine (l-isoleucine is absent in hemoglobin and therefore presumably it is important for the parasite to import this) in the RPMI medium do not affect growth of malaria parasite. Among others, there could be two possible reasons for this, either d-isoleucine is poorly absorbed by the parasite or the parasite-encoded DTD enzyme neutralizes expected toxicity of d-isoleucine. Our data indicate that the presence of the inhibitory compound 2 in the medium makes parasite growth vulnerable to higher d-isoleucine concentrations (Fig. 13B). This observation suggests that active PfDTD may be important for the malaria parasite in terms of overcoming d-amino acid-induced toxicity. Interestingly, compound 2 has been previously tested on J774A.1 cells (macrophage cell line) at up to 100 μm concentration, and it showed negligible cytotoxicity (28.Panchal R.G. Hermone A.R. Nguyen T.L. Wong T.Y. Schwarzenbacher R. Schmidt J. Lane D. McGrath C. Turk B.E. Burnett J. Aman M.J. Little S. Sausville E.A. Zaharevitz D.W. Cantley L.C. Liddington R.C. Gussio R. Bavari S. Nat. Struct. Mol. Biol. 2004; 11: 67-72Crossref PubMed Scopus (129) Google Scholar).In conclusion, we present a comprehensive mechanism for the deacylation reaction by the DTD class of proofreading enzymes. Our structural studies suggest how d-amino acid-charged tRNA may be recognized and processed by PfDTD. These studies also provide direct comparisons with the previously characterized Pab-NTD enzyme family. The description of multiple subsites within DTD active site pocket provides a first view of the structural architecture required by these enzymes to perform their editing functions. Our results also suggest that specific inhibitors against PfDTD may hinder parasite growth in the presence of d-amino acids. DTDs from pathogenic organisms like P. falciparum can therefore be explored further for their value as novel and unique targets for the focus of antimalarials. IntroductionAminoacyl-tRNA synthetases (aaRSs) transfer l-amino acids to their cognate tRNA and are essential in the protein translation process. However, at times aaRS enzymes can also attach d-amino acids to tRNA, and this mistake can be toxic to growing cells. Tyrosyl-tRNA synthetases from Escherichia coli and Bacillus subtilis (1.Calendar R. Berg P. Biochemistry. 1966; 5: 1681-1690Crossref PubMed Scopus (160) Google Scholar, 2.Calendar R. Berg P. Biochemistry. 1966; 5: 1690-1695Crossref PubMed Scopus (139) Google Scholar), tyrosyl-tRNA synthetases from Saccharomyces cerevisiae (3.Soutourina J. Blanquet S. Plateau P. J. Biol. Chem. 2000; 275: 11626-11630Abstract Full Text Full Text PDF PubMed Scopus (43) Google Scholar) and tryptophanyl/aspartyl-tRNA synthetases from S. cerevisiae (4.Soutourina J. Plateau P. Blanquet S. J. Biol. Chem. 2000; 275: 32535-32542Abstract Full Text Full Text PDF PubMed Scopus (109) Google Scholar) can transfer d-forms of their cognate amino acids onto relevant tRNAs. To avoid introduction of d-amino acids in the translation machinery, almost all cells have editing domains like d-tyrosyl-tRNATyr deacylase (DTD). 4The abbreviations used are: DTDd-tyrosyl-tRNATyr deacylasePfDTDP. falciparum DTDAaDTDA. aeolicus DTDEcDTDE. coli DTDHiDTDH. influenzae DTDHsDTDH. sapiens DTDA3Sseryl-3′-aminoadenosineA3Ytyrosyl-3′-aminoadenosineDAPI4′,6-diamidino-2-phenylindoleNTAnitrilotriacetic acidPEGpolyethylene glycolMES4-morpholineethanesulfonic acidPBSphosphate-buffered saliner.m.s.d.root mean-square deviation. This enzyme cleaves the bond between d-amino acids and tRNA (Fig. 1A) and is encoded by the dtd gene in E. coli (5.Soutourina J. Plateau P. Delort F. Peirotes A. Blanquet S. J. Biol. Chem. 1999; 274: 19109-19114Abstract Full Text Full Text PDF PubMed Scopus (58) Google Scholar) and by the dtd1 gene in S. cerevisiae (3.Soutourina J. Blanquet S. Plateau P. J. Biol. Chem. 2000; 275: 11626-11630Abstract Full Text Full Text PDF PubMed Scopus (43) Google Scholar). Homologs of dtd/dtd1 genes are found in many genomes (S. cerevisiae, Caenorhabditis elegans, mouse, human (5.Soutourina J. Plateau P. Delort F. Peirotes A. Blanquet S. J. Biol. Chem. 1999; 274: 19109-19114Abstract Full Text Full Text PDF PubMed Scopus (58) Google Scholar), but not in archaea (4.Soutourina J. Plateau P. Blanquet S. J. Biol. Chem. 2000; 275: 32535-32542Abstract Full Text Full Text PDF PubMed Scopus (109) Google Scholar). However, another dtd2 (previously named GEK1) gene homologous to dtd/dtd1 is found in archaea and plants (6.Wydau S. Ferri-Fioni M.L. Blanquet S. Plateau P. Nucleic Acids Res. 2007; 35: 930-938Crossref PubMed Scopus (17) Google Scholar, 7.Ferri-Fioni M.L. Fromant M. Bouin A.P. Aubard C. Lazennec C. Plateau P. Blanquet S. J. Biol. Chem. 2006; 281: 27575-27585Abstract Full Text Full Text PDF PubMed Scopus (24) Google Scholar). DTD enzymes exhibit broad specificity toward various d-amino acid-charged tRNAs (d-aa-tRNA) and are essentially inactive toward l-aa-tRNAs (2.Calendar R. Berg P. Biochemistry. 1966; 5: 1690-1695Crossref PubMed Scopus (139) Google Scholar). Human DTD, also called DUE-B, has a long C-terminal extension and seems to be involved in d-amino acid resistance by deacylating d-aa-tRNAs during tRNA export (8.Zheng G. Liu W. Gong Y. Yang H. Yin B. Zhu J. Xie Y. Peng X. Qiang B. Yuan J. Biochem. J. 2009; 417: 85-94Crossref PubMed Scopus (22) Google Scholar).Plasmodium parasites are causative agents of malaria, which affects >500 million people and claims ∼2 million lives annually (9.Snow R.W. Guerra C.A. Noor A.M. Myint H.Y. Hay S.I. Nature. 2005; 434: 214-217Crossref PubMed Scopus (2129) Google Scholar). In the Plasmodium falciparum genome, there are no sequence homologs for d-amino acid oxidase and d-Ser racemase, but a single copy of the dtd gene is present. PfDTD may therefore be responsible for detoxification of d-amino acids in this parasite. The molecular weight of PfDTD is ∼20 kDa, and the sequence identity between PfDTD and its human homolog (HsDUE-B) is ∼35%.Native DTD structures have been reported from Aquifex aeolicus (AaDTD: PDB code 2DBO), E. coli (EcDTD: PDB code 1JKE, Ref. 10.Ferri-Fioni M.L. Schmitt E. Soutourina J. Plateau P. Mechulam Y. Blanquet S. J. Biol. Chem. 2001; 276: 47285-47290Abstract Full Text Full Text PDF PubMed Scopus (50) Google Scholar), Haemophilus influenza (HiDTD: PDB code 1J7G, Ref. 11.Lim K. Tempczyk A. Bonander N. Toedt J. Howard A. Eisenstein E. Herzberg O. J. Biol. Chem. 2003; 278: 13496-13502Abstract Full Text Full Text PDF PubMed Scopus (22) Google Scholar), Homo sapiens (HsDTD: PDB code 2OKV, Ref. 12.Kemp M. Bae B. Yu J.P. Ghosh M. Leffak M. Nair S.K. J. Biol. Chem. 2007; 282: 10441-10448Abstract Full Text Full Text PDF PubMed Scopus (19) Google Scholar), and Leishmania major (LmDTD: PDB code 1TC5). A catalytic mechanism has also been proposed on the basis of mutagenesis and tRNA modeling onto DTDs (11.Lim K. Tempczyk A. Bonander N. Toedt J. Howard A. Eisenstein E. Herzberg O. J. Biol. Chem. 2003; 278: 13496-13502Abstract Full Text Full Text PDF PubMed Scopus (22) Google Scholar, 12.Kemp M. Bae B. Yu J.P. Ghosh M. Leffak M. Nair S.K. J. Biol. Chem. 2007; 282: 10441-10448Abstract Full Text Full Text PDF PubMed Scopus (19) Google Scholar). However, to date, there are no DTD-ligand complex structures known from any organism. Here, we report a whole set of crystal structures of DTD from P. falciparum complexed with adenosine and various d-amino acids. The crystal structures of native, ADP-bound, and d-amino acid-complexed PfDTDs provide key insights into the binding and recognition modes for various ligands. Based on the high resolution structures of PfDTD, we have also performed in silico inhibitor screening and present data for four compounds that inhibit parasite growth. We believe that our analysis not only provides a structural basis for the catalytic mechanism for this family of editing enzymes, but also highlights a possible new focus for the development of specific antimalarials.
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