Dihydrolipoamide acetyltransferase is a key factor mediating adhesion and invasion of host cells by Mycoplasma synoviae

Mycoplasma synoviae is a significant avian pathogen responsible for chronic respiratory diseases, arthritis, and infectious synovitis in chickens and turkeys. These infections result in substantial economic losses to the global poultry industry. Dihydrolipoamide acetyltransferase (E2) is a multifunctional protein that plays an indispensable role in energy metabolism and redox balance and is also a key virulence factor of various pathogens. In this study, we used the avian pathogen M. synoviae as a model to identify the role of the E2 protein in the colonization and invasion of host cells. First, we prepared the polyclonal antibody of recombinant E2 (rE2) protein and found that the rE2 antibody had a strong complement-activating ability. E2 was found to be distributed in the cytoplasm and cell membrane of M. synoviae by immunoelectron microscopy. E2 localized on the cell membrane is a key factor in the adhesion of M. synoviae and has good immunogenicity. Enzyme-linked immunosorbent assay showed that the binding of rE2 to membrane proteins of chicken embryo fibroblasts (DF-1) was dose-dependent, and antiserum effectively inhibited this binding ability. Furthermore, E2 interacted with various components of the host extracellular matrix (ECM) and promoted the conversion of plasminogen to plasmin through terephthalic acid (tPA). In addition, E2 can enhance the ability of M. synoviae to invade DF-1 cells, which was significantly reduced after treatment with anti-E2 serum. These results indicate that E2 is an adhesion- and invasion-related protein and may be involved in the pathogenesis of M. synoviae, which provides new ideas for studying the pathogenesis of M. synoviae and preparing subunit vaccines.