DnaK Functions as a Moonlighting Protein on the Surface of Mycoplasma hyorhinis Cells.

Yao Li,Yanna Wei,Zhigang Tu,Qiyan Xiong,Jia Wang,Yuan Gan,Zhixin Feng,Yanfei Yu,Jia Shao,Beibei Liu,Ting Yuan,Guoqing Shao

doi:10.3389/fmicb.2022.842058

Abstract

Mycoplasma hyorhinis is a common pathogen of swine and is also associated with various human tumors. It causes systemic inflammation, typically polyserositis and polyarthritis, in some infected pigs. However, the pathogenic mechanism of M. hyorhinis remains unclear. DnaK is a highly conserved protein belonging to the heat-shock protein 70 family of molecular chaperones, which plays important roles as a moonlighting protein in various bacteria. In the present study, we identified the surface exposure of M. hyorhinis DnaK. Two virulent strains expressed more DnaK on their surface than the avirulent strain. Thereafter, the potential moonlighting functions of DnaK were investigated. Recombinant M. hyorhinis DnaK (rMhr-DnaK) was found to be able to adhere to swine PK-15 cells and human NCI-H292 cells. It also bound to four extracellular matrix components—fibronectin, laminin, type IV collagen, and vitronectin—in a dose-dependent manner. ELISA demonstrated an interaction between rMhr-DnaK and plasminogen, which was significantly inhibited by a lysine analog, ε-aminocaproic acid. rMhr-DnaK-bound plasminogen was activated by tissue-type plasminogen activator (tPA), and the addition of rMhr-DnaK significantly enhanced the activation. Finally, a DnaK-specific antibody was detected in the serum of pigs immunized with inactivated vaccines, which indicated good immunogenicity of it. In summary, our findings imply that DnaK is an important multifunctional moonlighting protein in M. hyorhinis and likely participates extensively in the infection and pathogenesis processes of M. hyorhinis.

Highlights

Mycoplasma hyorhinis is a species of mycoplasmas, which are small-sized, cellwall-free, prokaryotic organisms
The Full-length DnaK gene was designed according to the amino acid sequence of DnaK of M. hyorhinis strain HUB-1 and optimized according to E. coli codon usage
The antibody could react to the DnaK from M. hyorhinis and purified rMhr-DnaK protein (Figure 1C)

Summary

Introduction

Mycoplasma hyorhinis is a species of mycoplasmas (class Mollicutes), which are small-sized, cellwall-free, prokaryotic organisms. It was once considered to be a harmless commensal bacteria colonizing the tonsils and respiratory tract epithelium; its pathogenicity was subsequently identified and confirmed. It is well recognized as a cause of polyserositis and polyathritis primarily in nurseryage pigs. It seems not to be a commensal bacteria wildly popular in human, but the infection proportion of M. hyorhinis has been reported to be significantly higher in cancer tissues than the tissues of patients without cancer (Huang et al, 2001; Vande Voorde et al, 2014a). M. hyorhinis infection increases the resistance of tumor cells to anticancer agents. Multidrug resistance (MDR) to various chemotherapeutic agents has been observed in M. hyorhinis-infected hepatocarcinoma cells, which depends on the interaction between a surface lipoprotein P37 of M. hyorhinis and annexin A2 of the cell (Liu et al, 2017)

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