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Honors & Awards

  • Fulbright Scholar. Funding for Ph.D. studies., Bureau of Educational and Cultural Affairs of the U.S. Department of State
  • National Program for Innovation and Research., National Observatory of Science, Technology and Innovation, Venezuela.
  • Program of Endorsement for Research., Universidad de Los Andes, Venezuela
  • Plan II Fellow. Junior Scientist Training Grant., Universidad de Los Andes, Venezuela
  • FONACYT Scholar. Funding for Master studies., Venezuelan Ministry of Science and Technology

Professional Education

  • Licenciado, Universidad De Los Andes (2006)
  • Master of Science, Universidad De Los Andes (2011)
  • Doctor of Philosophy, University of Washington (2018)


All Publications

  • Structure-guided discovery of selective methionyl-tRNA synthetase inhibitors with potent activity against Trypanosoma brucei RSC MEDICINAL CHEMISTRY Zhang, Z., Barros-Alvarez, X., Gillespie, J., Ranade, R. M., Huang, W., Shibata, S., Molasky, N. R., Faghih, O., Mushtaq, A., Choy, R. M., de Hostos, E., Hol, W. J., Verlinde, C. J., Buckner, F. S., Fan, E. 2020; 11 (8): 885?95

    View details for DOI 10.1039/d0md00057d

    View details for Web of Science ID 000560538900011

  • The crystal structure of the drug target Mycobacterium tuberculosis methionyl-tRNA synthetase in complex with a catalytic intermediate ACTA CRYSTALLOGRAPHICA SECTION F-STRUCTURAL BIOLOGY COMMUNICATIONS Barros-Alvarez, X., Turley, S., Ranade, R. M., Gillespie, J., Duster, N. A., Verlinde, C. J., Fan, E., Buckner, F. S., Hol, W. J. 2018; 74: 245?54


    Mycobacterium tuberculosis is a pathogenic bacterial infectious agent that is responsible for approximately 1.5 million human deaths annually. Current treatment requires the long-term administration of multiple medicines with substantial side effects. Lack of compliance, together with other factors, has resulted in a worrisome increase in resistance. New treatment options are therefore urgently needed. Here, the crystal structure of methionyl-tRNA synthetase (MetRS), an enzyme critical for protein biosynthesis and therefore a drug target, in complex with its catalytic intermediate methionyl adenylate is reported. Phenylalanine 292 of the M. tuberculosis enzyme is in an `out' conformation and barely contacts the adenine ring, in contrast to other MetRS structures where ring stacking occurs between the adenine and a protein side-chain ring in the `in' conformation. A comparison with human cytosolic MetRS reveals substantial differences in the active site as well as regarding the position of the connective peptide subdomain 1 (CP1) near the active site, which bodes well for arriving at selective inhibitors. Comparison with the human mitochondrial enzyme at the amino-acid sequence level suggests that arriving at inhibitors with higher affinity for the mycobacterial enzyme than for the mitochondrial enzyme might be achievable.

    View details for DOI 10.1107/S2053230X18003151

    View details for Web of Science ID 000429557300009

    View details for PubMedID 29633973

    View details for PubMedCentralID PMC5893993

  • Development of Methionyl-tRNA Synthetase Inhibitors as Antibiotics for Gram-Positive Bacterial Infections ANTIMICROBIAL AGENTS AND CHEMOTHERAPY Faghih, O., Zhang, Z., Ranade, R. M., Gillespie, J., Creason, S. A., Huang, W., Shibata, S., Barros-Alvarez, X., Verlinde, C. J., Hol, W. J., Fan, E., Buckner, F. S. 2017; 61 (11)


    Antibiotic-resistant bacteria are widespread and pose a growing threat to human health. New antibiotics acting by novel mechanisms of action are needed to address this challenge. The bacterial methionyl-tRNA synthetase (MetRS) enzyme is essential for protein synthesis, and the type found in Gram-positive bacteria is substantially different from its counterpart found in the mammalian cytoplasm. Both previously published and new selective inhibitors were shown to be highly active against Gram-positive bacteria with MICs of ?1.3 ?g/ml against Staphylococcus, Enterococcus, and Streptococcus strains. Incorporation of radioactive precursors demonstrated that the mechanism of activity was due to the inhibition of protein synthesis. Little activity against Gram-negative bacteria was observed, consistent with the fact that Gram-negative bacterial species contain a different type of MetRS enzyme. The ratio of the MIC to the minimum bactericidal concentration (MBC) was consistent with a bacteriostatic mechanism. The level of protein binding of the compounds was high (>95%), and this translated to a substantial increase in MICs when the compounds were tested in the presence of serum. Despite this, the compounds were very active when they were tested in a Staphylococcus aureus murine thigh infection model. Compounds 1717 and 2144, given by oral gavage, resulted in 3- to 4-log decreases in the bacterial load compared to that in vehicle-treated mice, which was comparable to the results observed with the comparator drugs, vancomycin and linezolid. In summary, the research describes MetRS inhibitors with oral bioavailability that represent a class of compounds acting by a novel mechanism with excellent potential for clinical development.

    View details for DOI 10.1128/AAC.00999-17

    View details for Web of Science ID 000413558300051

    View details for PubMedID 28848016

    View details for PubMedCentralID PMC5655057

  • Leishmania donovani tyrosyl-tRNA synthetase structure in complex with a tyrosyl adenylate analog and comparisons with human and protozoan counterparts BIOCHIMIE Barros-Alvarez, X., Kerchner, K. M., Koh, C., Turley, S., Pardon, E., Steyaert, J., Ranade, R. M., Gillespie, J., Zhang, Z., Verlinde, C. J., Fan, E., Buckner, F. S., Hol, W. J. 2017; 138: 124?36


    The crystal structure of Leishmania donovani tyrosyl-tRNA synthetase (LdTyrRS) in complex with a nanobody and the tyrosyl adenylate analog TyrSA was determined at 2.75 Å resolution. Nanobodies are the variable domains of camelid heavy chain-only antibodies. The nanobody makes numerous crystal contacts and in addition reduces the flexibility of a loop of LdTyrRS. TyrSA is engaged in many interactions with active site residues occupying the tyrosine and adenine binding pockets. The LdTyrRS polypeptide chain consists of two pseudo-monomers, each consisting of two domains. Comparing the two independent chains in the asymmetric unit reveals that the two pseudo-monomers of LdTyrRS can bend with respect to each other essentially as rigid bodies. This flexibility might be useful in the positioning of tRNA for catalysis since both pseudo-monomers in the LdTyrRS chain are needed for charging tRNATyr. An "extra pocket" (EP) appears to be present near the adenine binding region of LdTyrRS. Since this pocket is absent in the two human homologous enzymes, the EP provides interesting opportunities for obtaining selective drugs for treating infections caused by L. donovani, a unicellular parasite causing visceral leishmaniasis, or kala azar, which claims 20,000 to 30,000 deaths per year. Sequence and structural comparisons indicate that the EP is a characteristic which also occurs in the active site of several other important pathogenic protozoa. Therefore, the structure of LdTyrRS could inspire the design of compounds useful for treating several different parasitic diseases.

    View details for DOI 10.1016/j.biochi.2017.04.006

    View details for Web of Science ID 000403988300015

    View details for PubMedID 28427904

    View details for PubMedCentralID PMC5484532

  • Optimization of a binding fragment targeting the "enlarged methionine pocket" leads to potent Trypanosoma brucei methionyl-tRNA synthetase inhibitors BIOORGANIC & MEDICINAL CHEMISTRY LETTERS Huang, W., Zhang, Z., Ranade, R. M., Gillespie, J., Barros-Alvarez, X., Creason, S. A., Shibata, S., Verlinde, C. J., Hol, W. J., Buckner, F. S., Fan, E. 2017; 27 (12): 2702?7


    Potent inhibitors of Trypanosoma brucei methionyl-tRNA synthetase were previously designed using a structure-guided approach. Compounds 1 and 2 were the most active compounds in the cyclic and linear linker series, respectively. To further improve cellular potency, SAR investigation of a binding fragment targeting the "enlarged methionine pocket" (EMP) was performed. The optimization led to the identification of a 6,8-dichloro-tetrahydroquinoline ring as a favorable fragment to bind the EMP. Replacement of 3,5-dichloro-benzyl group (the EMP binding fragment) of inhibitor 2 using this tetrahydroquinoline fragment resulted in compound 13, that exhibited an EC50 of 4nM.

    View details for DOI 10.1016/j.bmcl.2017.04.048

    View details for Web of Science ID 000402472600012

    View details for PubMedID 28465105

    View details for PubMedCentralID PMC5542777

  • From Cells to Mice to Target: Characterization of NEU-1053 (SB443342) and Its Analogues for Treatment of Human African Trypanosomiasis ACS INFECTIOUS DISEASES Devine, W. G., Diaz-Gonzalez, R., Ceballos-Perez, G., Rojas, D., Satoh, T., Tear, W., Ranade, R. M., Barros-Alvarez, X., Hol, W. J., Buckner, F. S., Navarro, M., Pollastri, M. P. 2017; 3 (3): 225?36


    Human African trypanosomiasis is a neglected tropical disease that is lethal if left untreated. Existing therapeutics have limited efficacy and severe associated toxicities. 2-(2-(((3-((1H-Benzo[d]imidazol-2-yl)amino)propyl)amino)methyl)-4,6-dichloro-1H-indol-1-yl)ethan-1-ol (NEU-1053) has recently been identified from a high-throughput screen of >42,000 compounds as a highly potent and fast-acting trypanocidal agent capable of curing a bloodstream infection of Trypanosoma brucei in mice. We have designed a library of analogues to probe the structure-activity relationship and improve the predicted central nervous system (CNS) exposure of NEU-1053. We report the activity of these inhibitors of T. brucei, the efficacy of NEU-1053 in a murine CNS model of infection, and identification of the target of NEU-1053 via X-ray crystallography.

    View details for DOI 10.1021/acsinfecdis.6b00202

    View details for Web of Science ID 000396384800006

    View details for PubMedID 28110521

    View details for PubMedCentralID PMC5346068

  • Structure-guided design of novel Trypanosoma brucei Methionyl-tRNA synthetase inhibitors EUROPEAN JOURNAL OF MEDICINAL CHEMISTRY Huang, W., Zhang, Z., Barros-Alvarez, X., Koh, C., Ranade, R. M., Gillespie, J., Creason, S. A., Shibata, S., Verlinde, C. J., Hol, W. J., Buckner, F. S., Fan, E. 2016; 124: 1081?92


    A screening hit 1 against Trypanosoma brucei methionyl-tRNA synthetase was optimized using a structure-guided approach. The optimization led to the identification of two novel series of potent inhibitors, the cyclic linker and linear linker series. Compounds of both series were potent in a T. brucei growth inhibition assay while showing low toxicity to mammalian cells. The best compound of each series, 16 and 31, exhibited EC50s of 39 and 22 nM, respectively. Compounds 16 and 31 also exhibited promising PK properties after oral dosing in mice. Moreover, compound 31 had moderately good brain permeability, with a brain/plasma ratio of 0.27 at 60 min after IP injection. This study provides new lead compounds for arriving at new treatments of human African trypanosomiasis (HAT).

    View details for DOI 10.1016/j.ejmech.2016.10.024

    View details for Web of Science ID 000388544600085

    View details for PubMedID 27788467

    View details for PubMedCentralID PMC5120670

  • The glycosomal-membrane associated phosphoglycerate kinase isoenzyme A plays a role in sustaining the glucose flux in Trypanosoma cruzi epimastigotes. Molecular and biochemical parasitology Barros-Álvarez, X. n., Cáceres, A. J., Ruiz, M. T., Michels, P. A., Concepción, J. L., Quiñones, W. n. 2015; 200 (1-2): 5?8


    In Trypanosoma cruzi three isoenzymes of phosphoglycerate kinase (PGK) are found which are simultaneously expressed: the cytosolic isoenzyme PGKB as well as two glycosomal enzymes, PGKA and PGKC. In this paper, we show that PGKA in T. cruzi epimastigotes is associated to the glycosomal membrane; it is responsible for about 23% of the glycosomal PGK activity, the fraction that remains in the pellet after osmotic shock treatment of purified organelles, in contrast to the 77% soluble activity that is mainly attributed to PGKC. Antibodies against the unique 80 amino-acid insertion of PGKA blocked almost completely the glucose consumption by epimastigotes that were partially permeabilized with digitonin. These results indicate that PGKA is the predominant isoenzyme for sustaining glycolysis through the glycosomes of these parasites.

    View details for DOI 10.1016/j.molbiopara.2015.04.003

    View details for PubMedID 25917939

  • Glycosomal Targets for Anti-Trypanosomatid Drug Discovery CURRENT MEDICINAL CHEMISTRY Barros-Alvarez, X., Gualdron-Lopez, M., Acosta, H., Caceres, A. J., Graminha, M. S., Michels, P. M., Concepcion, J. L., Quinones, W. 2014; 21 (15): 1679?1706


    Glycosomes are peroxisome-related organelles found in all kinetoplastid protists, including the human pathogenic species of the family Trypanosomatidae: Trypanosoma brucei, Trypanosoma cruzi and Leishmania spp. Glycosomes are unique in containing the majority of the glycolytic/gluconeogenic enzymes, but they also possess enzymes of several other important catabolic and anabolic pathways. The different metabolic processes are connected by shared cofactors and some metabolic intermediates, and their relative importance differs between the parasites or their distinct lifecycle stages, dependent on the environmental conditions encountered. By genetic or chemical means, a variety of glycosomal enzymes participating in different processes have been validated as drug targets. For several of these enzymes, as well as others that are likely crucial for proliferation, viability or virulence of the parasites, inhibitors have been obtained by different approaches such as compound libraries screening or design and synthesis. The efficacy and selectivity of some initially obtained inhibitors of parasite enzymes were further optimized by structure-activity relationship analysis, using available protein crystal structures. Several of the inhibitors cause growth inhibition of the clinically relevant stages of one or more parasitic trypanosomatid species and in some cases exert therapeutic effects in infected animals. The integrity of glycosomes and proper compartmentalization of at least several matrix enzymes is also crucial for the viability of the parasites. Therefore, proteins involved in the assembly of the organelles and transmembrane passage of substrates and products of glycosomal metabolism offer also promise as drug targets. Natural products with trypanocidal activity by affecting glycosomal integrity have been reported.

    View details for DOI 10.2174/09298673113209990139

    View details for Web of Science ID 000334356600003

    View details for PubMedID 23834165

  • The phosphoglycerate kinase isoenzymes have distinct roles in the regulation of carbohydrate metabolism in Trypanosoma cruzi. Experimental parasitology Barros-Álvarez, X. n., Cáceres, A. J., Michels, P. A., Concepción, J. L., Quiñones, W. n. 2014; 143: 39?47


    The glycolytic enzyme phosphoglycerate kinase (PGK) is present in Trypanosoma cruzi as three isoenzymes, two of them located inside glycosomes (PGKA and PGKC) and another one in the cytosol (PGKB). The three isoenzymes are expressed at all stages of the life cycle of the parasite. A heterologous expression system for PGKA (rPGKA) was developed and the substrate affinities of the natural and recombinant PGKA isoenzyme were determined. Km values measured for 3-phosphoglycerate (3PGA) were 174 and 850 ?M, and for ATP 217 and 236 ?M, for the natural and recombinant enzyme, respectively. No significant differences were found between the two forms of the enzyme. The rPGKA was inhibited by Suramin with Ki values of 10.08 ?M and 12.11 ?M for ATP and 3PGA, respectively, and the natural enzyme was inhibited at similar values. A site-directed mutant was created in which the 80 amino acids PGKA sequence, present as a distinctive insertion in the N-terminal domain, was deleted. This internally truncated PGKA showed the same Km values and specific activity as the full-length rPGKA. The natural PGKC isoenzyme was purified from epimastigotes and separated from PGKA through molecular exclusion chromatography and its kinetic characteristics were determined. The Km value obtained for 3PGA was 192 ?M, and 10 ?M for ATP. Contrary to PGKA, the activity of PGKC is tightly regulated by ATP (substrate inhibition) with a Ki of 270 ?M, suggesting a role for this isoenzyme in regulating metabolic fluxes inside the glycosomes.

    View details for DOI 10.1016/j.exppara.2014.05.010

    View details for PubMedID 24858924

  • Leishmania mexicana: LACK (Leishmania homolog of receptors for activated C-kinase) is a plasminogen binding protein. Experimental parasitology Gómez-Arreaza, A. n., Acosta, H. n., Barros-Álvarez, X. n., Concepción, J. L., Albericio, F. n., Avilan, L. n. 2011; 127 (4): 752?61


    Leishmania mexicana is able to interact with the fibrinolytic system through its component plasminogen, the zymogenic form of the protease plasmin. In this study a new plasminogen binding protein of this parasite was identified: LACK, the Leishmania homolog of receptors for activated C-kinase. Plasminogen binds recombinant LACK with a K(d) value of 1.6±0.4 ?M, and binding is lysine-dependent since it is inhibited by the lysine analog ?-aminocaproic acid. Inhibition studies with specific peptides and plasminogen binding activity of a mutated recombinant LACK have highlighted the internal motif (260)VYDLESKAV(268), similar to those found in several enolases, as involved in plasminogen binding. Recombinant LACK and secreted proteins, in medium conditioned by parasites, enhance plasminogen activation to plasmin by the tissue plasminogen activator (t-PA). In addition to its localization in the cytosol, in the microsomal fraction and as secreted protein in conditioned medium, LACK was also localized on the external surface of the membrane. The results presented here suggest that LACK might bind and enhance plasminogen activation in vivo promoting the formation of plasmin. Plasminogen binding of LACK represents a new function for this protein and might contribute to the invasiveness of the parasite.

    View details for DOI 10.1016/j.exppara.2011.01.008

    View details for PubMedID 21272581

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