A Histone-Like Protein of Mycobacteria Possesses Ferritin Superfamily Protein-Like Activity and Protects against DNA Damage by Fenton Reaction

Masaki Takatsuka,Mayuko Osada-Oka,Tetsuo Arakawa,Mamiko Niki,Yukiko Nishiuchi,Anura Rambukkana,Kazuhiro Iwai,Yoshihiro Shimoji,Eisuke F Satoh,Hisashi Ogura,Sohkichi Matsumoto,Masayasu Inoue,Kazuo Kobayashi,Kengo Kitadokoro

doi:10.1371/journal.pone.0020985

Abstract

Iron is an essential metal for living organisms but its level must be strictly controlled in cells, because ferrous ion induces toxicity by generating highly active reactive oxygen, hydroxyl radicals, through the Fenton reaction. In addition, ferric ion shows low solubility under physiological conditions. To overcome these obstacles living organisms possess Ferritin superfamily proteins that are distributed in all three domains of life: bacteria, archaea, and eukaryotes. These proteins minimize hydroxyl radical formation by ferroxidase activity that converts Fe2+ into Fe3+ and sequesters iron by storing it as a mineral inside a protein cage. In this study, we discovered that mycobacterial DNA-binding protein 1 (MDP1), a histone-like protein, has similar activity to ferritin superfamily proteins. MDP1 prevented the Fenton reaction and protects DNA by the ferroxidase activity. The K m values of the ferroxidase activity by MDP1 of Mycobacterium bovis bacillus Calmette-Guérin (BCG-3007c), Mycobacterium tuberculosis (Rv2986c), and Mycobacterium leprae (ML1683; ML-LBP) were 0.292, 0.252, and 0.129 mM, respectively. Furthermore, one MDP1 molecule directly captured 81.4±19.1 iron atoms, suggesting the role of this protein in iron storage. This study describes for the first time a ferroxidase-iron storage protein outside of the ferritin superfamily proteins and the protective role of this bacterial protein from DNA damage.

Highlights

Iron is an essential element for virtually all living organisms, and is convertible between the ferrous ion (Fe2+) and ferric ion (Fe3+) under physiological pH
We analyzed the potential interaction between mycobacterial DNA-binding protein 1 (MDP1) of Mycobacterium bovis bacillus Calmette Guerin (BCG) (BCG-MDP1) and each ligand by measuring surface plasmon resonance (SPR) with a BIAcore 2000 biosensor
It was reported that protein-metal interaction changes the protein structure, which in turn causes the changes of SPR [25]

Summary

Introduction

Iron is an essential element for virtually all living organisms, and is convertible between the ferrous ion (Fe2+) and ferric ion (Fe3+) under physiological pH. Living organisms employ this feature of iron for the catalytic centers of several critical enzymes, such as ribonucleotide reductase for the synthesis of DNA substrates and cytochromes involved in electron transport in respiration. Fe2+ is a reductant and generates reactive oxygen species (ROS) and reactive nitrogen species (RNS), which damage most cell components, including DNA, membranes, and proteins. The hydroxyl radical (NOH) is known as most reactive species in ROS and toxic for the cells. The hydroxyl radical is generated via the non-enzymatic Fenton reaction: Fe2zzH2O2?Fe3zzHO{z.OH

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Results

Conclusion