Proteomic analysis of Giardia lamblia and Trichomonas vaginalis flagella reveal unique post-translational modifications in tubulin that provide clues to regulation of their motilities

All eukaryotic flagella are made of microtubules and driven by dynein motor proteins. However, every organism is unique in terms of its flagellar waveform, beat frequency, and its general motility pattern. With recent research, it is becoming clear that despite overall conservation in flagellar structure, the pattern of tubulin post-translational modifications within the flagella are diverse and may contribute to variations in their patterns of motility. In this study, we have analyzed the tubulin post-translational modification in the protozoan parasites Giardia lamblia and Trichomonas vaginalis using global, untargeted mass spectrometry. We show that tubulin monoglycylation is a modification localized to the flagella present in G. lamblia but absent in T. vaginalis. We also show the presence of glutamylated tubulin in both G. lamblia and T. vaginalis. Using MS/MS, we were also able to identify the previously unknown sites of monoglycylation in beta-tubulin at E438 and E439 in G. lamblia. Using isolated flagella, we also characterized the flagellar proteome in G. lamblia and T. vaginalis and identified 475 proteins in G. lamblia and 386 proteins in T. vaginalis flagella. Altogether, the flagellar proteomes as well as the sites of tubulin PTMs in these organisms, reveal potential mechanisms in regulating flagellar motilities in these neglected protozoan parasites.