The Entamoeba histolytica Dnmt2 homolog (Ehmeth) confers resistance to nitrosative stress

Eukaryot Cell. 2014 Apr;13(4):494-503. doi: 10.1128/EC.00031-14. Epub 2014 Feb 21.

Abstract

Nitric oxide (NO) has antimicrobial properties against many pathogens due to its reactivity as an S-nitrosylating agent. It inhibits many of the key enzymes that are involved in the metabolism and virulence of the parasite Entamoeba histolytica through S-nitrosylation of essential cysteine residues. Very little information is available on the mechanism of resistance to NO by pathogens in general and by this parasite in particular. Here, we report that exposure of the parasites to S-nitrosoglutathione (GSNO), an NO donor molecule, strongly reduces their viability and protein synthesis. However, the deleterious effects of NO were significantly reduced in trophozoites overexpressing Ehmeth, the cytosine-5 methyltransferase of the Dnmt2 family. Since these trophozoites also exhibited high levels of tRNA(Asp) methylation, the high levels suggested that Ehmeth-mediated tRNA(Asp) methylation is part of the resistance mechanism to NO. We previously reported that enolase, another glycolytic enzyme, binds to Ehmeth and inhibits its activity. We observed that the amount of Ehmeth-enolase complex was significantly reduced in GSNO-treated E. histolytica, which explains the aforementioned increase of tRNA methylation. Specifically, we demonstrated via site-directed mutagenesis that cysteine residues 228 and 229 of Ehmeth are susceptible to S-nitrosylation and are crucial for Ehmeth binding to enolase and for Ehmeth-mediated resistance to NO. These results indicate that Ehmeth has a central role in the response of the parasite to NO, and they contribute to the growing evidence that NO is a regulator of epigenetic mechanisms.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Cysteine / chemistry
  • Cysteine / metabolism
  • DNA (Cytosine-5-)-Methyltransferases / genetics*
  • DNA (Cytosine-5-)-Methyltransferases / metabolism
  • Drug Resistance / genetics*
  • Entamoeba histolytica / drug effects
  • Entamoeba histolytica / genetics*
  • Entamoeba histolytica / metabolism
  • Epigenesis, Genetic
  • Methylation
  • Mutagenesis, Site-Directed
  • Nitric Oxide / metabolism
  • Nitric Oxide / pharmacology
  • Nitric Oxide Donors / metabolism
  • Nitric Oxide Donors / pharmacology*
  • Phosphopyruvate Hydratase / genetics
  • Phosphopyruvate Hydratase / metabolism
  • Protein Binding
  • Protein Biosynthesis / drug effects
  • Protozoan Proteins / genetics*
  • Protozoan Proteins / metabolism
  • RNA, Transfer / metabolism
  • S-Nitrosoglutathione / metabolism
  • S-Nitrosoglutathione / pharmacology*
  • Signal Transduction
  • Stress, Physiological
  • Trophozoites / drug effects
  • Trophozoites / growth & development
  • Trophozoites / metabolism

Substances

  • Nitric Oxide Donors
  • Protozoan Proteins
  • Nitric Oxide
  • S-Nitrosoglutathione
  • RNA, Transfer
  • DNA (Cytosine-5-)-Methyltransferases
  • Phosphopyruvate Hydratase
  • Cysteine