A 14.7 kDa protein from Francisella tularensis subsp. novicida (named FTN_1133), involved in the response to oxidative stress induced by organic peroxides, is not endowed with thiol-dependent peroxidase activity

PLoS One. 2014 Jun 24;9(6):e99492. doi: 10.1371/journal.pone.0099492. eCollection 2014.

Abstract

Francisella genus comprises Gram-negative facultative intracellular bacteria that are among the most infectious human pathogens. A protein of 14.7 KDa named as FTN_1133 was previously described as a novel hydroperoxide resistance protein in F. tularensis subsp. novicida, implicated in organic peroxide detoxification and virulence. Here, we describe a structural and biochemical characterization of FTN_1133. Contrary to previous assumptions, multiple amino acid sequence alignment analyses revealed that FTN_1133 does not share significant similarity with proteins of the Ohr/OsmC family or any other Cys-based, thiol dependent peroxidase, including conserved motifs around reactive cysteine residues. Circular dichroism analyses were consistent with the in silico prediction of an all-α-helix secondary structure. The pKa of its single cysteine residue, determined by a monobromobimane alkylation method, was shown to be 8.0±0.1, value that is elevated when compared with other Cys-based peroxidases, such as peroxiredoxins and Ohr/OsmC proteins. Attempts to determine a thiol peroxidase activity for FTN_1133 failed, using both dithiols (DTT, thioredoxin and lipoamide) and monothiols (glutathione or 2-mercaptoethanol) as reducing agents. Heterologous expression of FTN_1133 gene in ahpC and oxyR mutants of E. coli showed no complementation. Furthermore, analysis of FTN_1133 protein by non-reducing SDS-PAGE showed that an inter-molecular disulfide bond (not detected in Ohr proteins) can be generated under hydroperoxide treatment, but the observed rates were not comparable to those observed for other thiol-dependent peroxidases. All the biochemical and structural data taken together indicated that FTN_1133 displayed distinct characteristics from other thiol dependent peroxidases and, therefore, suggested that FTN_1133 is not directly involved in hydroperoxide detoxification.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Bacterial Proteins / chemistry
  • Bacterial Proteins / metabolism
  • Circular Dichroism
  • Conserved Sequence
  • Francisella tularensis / metabolism*
  • Hydrogen Peroxide / pharmacology*
  • Models, Molecular
  • Oxidants / pharmacology*
  • Oxidative Stress
  • Peroxidases / chemistry*
  • Peroxidases / metabolism*
  • Protein Structure, Secondary

Substances

  • Bacterial Proteins
  • Oxidants
  • Hydrogen Peroxide
  • Peroxidases

Grants and funding

This work was supported by grants 2007/58147-6 and 2013/07937-8 from the Fundação de Amparo à Pesquisado Estado de São Paulo (FAPESP) and by a post-doctoral fellowship from FAPESP, process number 2012/21722-1, to Diogo de Abreu Meireles. The funder (FAPESP) had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.