The ventral disc is a specialised adhesive structure of the parasitic protozoan Giardia lamblia that is composed of about 100 microtubules (MTs); these are uniformly distributed in a spiral, forming a dome-shaped organelle. Although the disc architecture has been characterised, it remains poorly understood whether other components contribute to its MT hyperstability. By using biochemical fractionation and proteomic analysis, Scott Dawson and colleagues (Nosala, Hagen, Hilton et al., 2020) now identify 53 new disc-associated proteins (DAPs). Moreover, C-terminal GFP-tagging of these proteins allowed the differentiation of their distribution across five different regions of the ventral disc: the MT spiral array (body), the disc margin, the ventral groove, the dense bands and the overlap zone. Some of these DAPs are homologues of microtubule-associated proteins (MAPs) and microtubule inner proteins (MIPs). Interestingly, only two DAPs have known MT-binding domains, which could point to the existence of additional MT-binding motifs. Finally, CRISPR-mediated knockdown (KD) of DAP5188 and DAP6751 leads to the loss of ventral disc hyperstability; in fact, upon nocodazole treatment, the ventral disc is dissociated in the DAP5188 KD. Thus, this study provides insights into how DAPs contribute to the function, organisation and characteristic hyperstability of the ventral disc of G. lamblia.
