Insights in tubulin-like structures of the poultry pathogen Mycoplasmoides gallisepticum

Long, unique cytoskeleton-like structures resembling microtubules of higher eukaryotes were discovered in Mycoplasmoides gallisepticum (former taxonomy name Mycoplasma gallisepticum), one of the smallest prokaryotes. Identifying the structural components of these formations is of great interest. These structures may contribute to the motility of M. gallisepticum cells. Since proteins involved in motility are potential targets for new antibacterial therapies, studying them is crucial. M. gallisepticum causes chronic respiratory diseases in poultry, leading to significant economic losses. Therefore, combating this mycoplasma holds serious practical importance. Here, using immunoprecipitation with anti-tubulin antibodies and mass spectrometry, a previously undetected "tubulin-like" protein in the M. gallisepticum cell lysate was identified as type I glyceraldehyde-3-phosphate dehydrogenase (GapD). Moreover, this protein was one of the 10 major components of the Triton-insoluble fraction of the M. gallisepticum proteins. Bioinformatics analysis revealed both similarities and differences between the primary and spatial structures of tubulins and GapD. While GapD is not a classical tubulin-like protein, it is the only Triton-insoluble component exhibiting certain tubulin-like characteristics. The pure GapD protein formed loose filament-like structures in KGA buffer. Finally, GapD was directly recognized by TU-01 antibodies in its recombinant and native forms. Therefore, GapD may be considered as a candidate for the role of a protein involved in the formation of cytoskeleton-like structures, with functions extending beyond its traditional role in glycolysis. Similar to certain enzymes found in Mycoplasma mobile, other Triton-insoluble proteins in M. gallisepticum, although primarily enzymatic, are also likely candidates for components of cytoskeleton-like structures.