Overexpression of a monomeric form of the bovine odorant-binding protein protects Escherichia coli from chemical-induced oxidative stress

Abstract

Mammalian odorant-binding proteins (OBPs) are soluble lipocalins produced in the nasal mucosa and in other epithelial tissues of several animal species, where they are supposed to serve as scavengers for small structurally unrelated hydrophobic molecules. These would include odorants and toxic aldehydes like 4-hydroxy-2-nonenal (HNE), which are end products of lipid peroxidation; therefore OBP might physiologically contribute to preserve the integrity of epithelial tissues under oxidative stress conditions by removing toxic compounds from the environment and, eventually, driving them to the appropriate degradative pathways. With the aim of developing a biological model based on a living organism for the investigation of the antioxidant properties of OBP, here we asked whether the overexpression of the protein could confer protection from chemical-induced oxidative stress in Escherichia coli. To this aim, bacteria were made to overexpress either GCC-bOBP, a redesigned monomeric mutant of bovine OBP, or its amino-terminal 6-histidine-tagged version 6H-GCC-bOBP. After inducing overexpression for 4 h, bacterial cells were diluted in fresh culture media, and their growth curves were followed in the presence of hydrogen peroxide (H₂O₂) and tert-Butyl hydroperoxide (tBuOOH), two reactive oxygen species whose toxicity is mainly due to lipid peroxidation, and menadione, a redox-cycling drug producing the superoxide ion. GCC-bOBP and 6H-GCC-bOBP were found to protect bacterial cells from the insulting agents H₂O₂ and tBuOOH but not from menadione. The obtained data led us to hypothesize that the presence of overexpressed OBP may contribute to protect bacterial cells against oxidative stress probably by sequestering toxic compounds locally produced during the first replication cycles by lipid peroxidation, before bacteria activate their appropriate enzyme-based antioxidative mechanisms.

Keywords::

• lipocalins
• lipid peroxidation
• 4-hydroxy-2-nonenal
• reactive oxygen species
• unsaturated fatty acids

Acknowledgments

We thank Dr. Héctor Malagón (IFC, UNAM) for his help in antibody production and Dr. Virna Conti (Univ. of Parma) for technical assistance.

Declaration of interest

The authors report no declarations of interest. The authors alone are responsible for the content and writing of the paper.

This work was partially supported by grants Consejo Nacional de Ciencia y Tecnología (CONACyT, Mexico) 128110 and Dirección General de Asuntos del Personal Académico (DGAPA-UNAM, Mexico) IN203311-3 to D.G.-H. The work was also supported by the bilateral research project ‘MX11MO10’ funded by CONACyT (Mexico) and the Italian Minister of Foreign Affairs (MAE, Italy). CONACyT also supported with a fellowship the Ph.D. studies of A.M.-M. (Biochemical Sciences Graduate Program at UNAM, fellowship No 176940).