title: Origin of robustness in generating drug-resistant malaria parasites.
abstract: Biological robustness allows mutations to accumulate while maintaining functional phenotypes. Despite its crucial role in evolutionary processes, the mechanistic details of how robustness originates remain elusive. Using an evolutionary trajectory analysis approach, we demonstrate how robustness evolved in malaria parasites under selective pressure from an antimalarial drug inhibiting the folate synthesis pathway. A series of four nonsynonymous amino acid substitutions at the targeted enzyme, dihydrofolate reductase (DHFR), render the parasites highly resistant to the antifolate drug pyrimethamine. Nevertheless, the stepwise gain of these four dhfr mutations results in tradeoffs between pyrimethamine resistance and parasite fitness. Here, we report the epistatic interaction between dhfr mutations and amplification of the gene encoding the first upstream enzyme in the folate pathway, GTP cyclohydrolase I (GCH1). gch1 amplification confers low level pyrimethamine resistance and would thus be selected for by pyrimethamine treatment. Interestingly, the gch1 amplification can then be co-opted by the parasites because it reduces the cost of acquiring drug-resistant dhfr mutations downstream in the same metabolic pathway. The compensation of compromised fitness by extra GCH1 is an example of how robustness can evolve in a system and thus expand the accessibility of evolutionary trajectories leading toward highly resistant alleles. The evolution of robustness during the gain of drug-resistant mutations has broad implications for both the development of new drugs and molecular surveillance for resistance to existing drugs.
authors.affiliation: Department of Biochemistry, Faculty of Science, Mahidol University, Bangkok, Thailand.
authors.forename: Krittikorn
authors.initials: K
authors.lastname: Kümpornsin
authors.affiliation: Department of Biochemistry, Faculty of Science, Mahidol University, Bangkok, ThailandBiophysics Group, Department of Physics, Faculty of Science, Mahidol University, Bangkok, Thailand.
authors.forename: Charin
authors.initials: C
authors.lastname: Modchang
authors.affiliation: Department of Microbiology and Immunology, Weill Cornell Medical College, New York, NY.
authors.forename: Adina
authors.initials: A
authors.lastname: Heinberg
authors.affiliation: Department of Microbiology and Immunology, Columbia University College of Physicians and Surgeons, New York, NY.
authors.forename: Eric H
authors.initials: EH
authors.lastname: Ekland
authors.affiliation: Department of Biochemistry, Faculty of Science, Mahidol University, Bangkok, Thailand.
authors.forename: Piyaporn
authors.initials: P
authors.lastname: Jirawatcharadech
authors.affiliation: Department of Biochemistry, Faculty of Science, Mahidol University, Bangkok, Thailand.
authors.forename: Pornpimol
authors.initials: P
authors.lastname: Chobson
authors.affiliation: National Center for Genetic Engineering and Biotechnology, National Science and Technology Development Agency, Pathum Thani, Thailand.
authors.forename: Nattida
authors.initials: N
authors.lastname: Suwanakitti
authors.affiliation: National Center for Genetic Engineering and Biotechnology, National Science and Technology Development Agency, Pathum Thani, Thailand.
authors.forename: Sastra
authors.initials: S
authors.lastname: Chaotheing
authors.affiliation: Department of Biochemistry, Faculty of Science, Mahidol University, Bangkok, Thailand.
authors.forename: Prapon
authors.initials: P
authors.lastname: Wilairat
authors.affiliation: Department of Microbiology and Immunology, Weill Cornell Medical College, New York, NY.
authors.forename: Kirk W
authors.initials: KW
authors.lastname: Deitsch
authors.affiliation: National Center for Genetic Engineering and Biotechnology, National Science and Technology Development Agency, Pathum Thani, Thailand.
authors.forename: Sumalee
authors.initials: S
authors.lastname: Kamchonwongpaisan
authors.affiliation: Department of Microbiology and Immunology, Columbia University College of Physicians and Surgeons, New York, NYDivision of Infectious Diseases, Department of Medicine, Columbia University College of Physicians and Surgeons, New York, NY.
authors.forename: David A
authors.initials: DA
authors.lastname: Fidock
authors.affiliation: Department of Microbiology and Immunology, Weill Cornell Medical College, New York, NYDivision of Infectious Diseases, Department of Medicine, Weill Cornell Medical College, New York, NY.
authors.forename: Laura A
authors.initials: LA
authors.lastname: Kirkman
authors.affiliation: National Center for Genetic Engineering and Biotechnology, National Science and Technology Development Agency, Pathum Thani, Thailand.
authors.forename: Yongyuth
authors.initials: Y
authors.lastname: Yuthavong
authors.affiliation: Department of Biochemistry, Faculty of Science, Mahidol University, Bangkok, ThailandCenter of Excellence in Malaria, Faculty of Tropical Medicine, Mahidol University, Bangkok, Thailand thanat.cho@mahidol.edu.
authors.forename: Thanat
authors.initials: T
authors.lastname: Chookajorn
mesh_terms: D019943:Amino Acid Substitution; D000962:Antimalarials / Q000494:pharmacology; D005075:Biological Evolution; D004351:Drug Resistance; D004843:Epistasis, Genetic; D006136:GTP Cyclohydrolase / Q000235:genetics* / Q000378:metabolism*; D017125:Genes, Protozoan; D056084:Genetic Fitness; D006801:Humans; D016778:Malaria, Falciparum / Q000188:drug therapy; D010963:Plasmodium falciparum / Q000235:genetics / Q000502:physiology*; D011739:Pyrimethamine / Q000494:pharmacology; D015398:Signal Transduction / Q000187:drug effects; D013762:Tetrahydrofolate Dehydrogenase / Q000235:genetics* / Q000378:metabolism*
chemical_list: D000962:Antimalarials; D013762:Tetrahydrofolate Dehydrogenase; D006136:GTP Cyclohydrolase; D011739:Pyrimethamine
keywords: drug resistance; evolution; malaria; robustness
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