The crystal structures of the tryparedoxin-tryparedoxin peroxidase couple unveil the structural determinants of Leishmania detoxification pathway

PLoS Negl Trop Dis. 2012;6(8):e1781. doi: 10.1371/journal.pntd.0001781. Epub 2012 Aug 21.

Abstract

Leishmaniasis is a neglected disease caused by Leishmania, an intracellular protozoan parasite which possesses a unique thiol metabolism based on trypanothione. Trypanothione is used as a source of electrons by the tryparedoxin/tryparedoxin peroxidase system (TXN/TXNPx) to reduce the hydroperoxides produced by macrophages during infection. This detoxification pathway is not only unique to the parasite but is also essential for its survival; therefore, it constitutes a most attractive drug target. Several forms of TXNPx, with very high sequence identity to one another, have been found in Leishmania strains, one of which has been used as a component of a potential anti-leishmanial polyprotein vaccine. The structures of cytosolic TXN and TXNPx from L. major (LmTXN and LmTXNPx) offer a unique opportunity to study peroxide reduction in Leishmania parasites at a molecular level, and may provide new tools for multienzyme inhibition-based drug discovery. Structural analyses bring out key structural features to elucidate LmTXN and LmTXNPx function. LmTXN displays an unusual N-terminal α-helix which allows the formation of a stable domain-swapped dimer. In LmTXNPx, crystallized in reducing condition, both the locally unfolded (LU) and fully folded (FF) conformations, typical of the oxidized and reduced protein respectively, are populated. The structural analysis presented here points to a high flexibility of the loop that includes the peroxidatic cysteine which facilitates Cys52 to form an inter-chain disulfide bond with the resolving cysteine (Cys173), thereby preventing over-oxidation which would inactivate the enzyme. Analysis of the electrostatic surface potentials of both LmTXN and LmTXNPx unveils the structural elements at the basis of functionally relevant interaction between the two proteins. Finally, the structural analysis of TXNPx allows us to identify the position of the epitopes that make the protein antigenic and therefore potentially suitable to be used in an anti-leishmanial polyprotein vaccine.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Crystallography, X-Ray
  • Hydrogen Peroxide / metabolism
  • Hydrogen Peroxide / toxicity
  • Inactivation, Metabolic
  • Leishmania major / chemistry
  • Leishmania major / drug effects
  • Leishmania major / enzymology*
  • Leishmania major / metabolism
  • Models, Molecular
  • Molecular Sequence Data
  • Peroxidases / chemistry*
  • Peroxidases / metabolism
  • Protein Conformation
  • Protein Multimerization
  • Protozoan Proteins / chemistry*
  • Protozoan Proteins / metabolism
  • Sequence Alignment
  • Static Electricity
  • Thioredoxins / chemistry*
  • Thioredoxins / metabolism

Substances

  • Protozoan Proteins
  • tryparedoxin
  • Thioredoxins
  • Hydrogen Peroxide
  • Peroxidases
  • tryparedoxin peroxidase

Grant support

The present studies have been partially supported from Ministero dell'Istruzione, dell'Università e della Ricerca of Italy (FIRB RBFR08F41U); from Istituto Pasteur, Fondazione Cenci Bolognetti to AB; from the Italian Ministry of Economy and Finance (CNR-Project FaReBio di Qualità) to GC; and from the European Community's Seventh Framework Programme (FP7/2007-2013) under grant agreement n° 226716. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.