Divergent functions of late ESCRT components in Giardia lamblia: Insights from subcellular distributions and protein interactions

Giardia lamblia, a human gut pathogen, possesses a minimal ESCRT (Endosomal Sorting Complex Required for Transport) machinery. Paradoxically, there are multiple paralogues of some late-ESCRT components- three paralogues for Vps4, GlVps4a, GlVps4b, and GlVps4c, and two for Vps46, GlVps46a and GlVps46b. This study addressed whether these paralogues can potentially discharge distinct cellular functions by determining the subcellular distribution of the paralogues in trophozoites and during encystation. Consistent with the distribution of orthologues from model organisms, most of these components were found to be associated with various cellular membranes, particularly in regions of acute membrane bending. Some of these paralogues are also associated with microtubule structures, such as cytoplasmic axonemes and the median body. Considering their diverse sub-cellular distributions, it is likely that they perform non-overlapping functions within the cell. Further, their redistribution during encystation indicates that they may play a role in the morphological and functional changes accompanying this transition. The study also characterized GlIst1, an ESCRT-III accessory protein that undergoes unique post-translational myristoylation at lysine 43. GlIst1 selectively interacts with GlVps4b through non-canonical MIT-MIM interactions. GlIst1 also exhibits selective interaction with GlVps46b. Such selective interaction of GlIst1 with only specific paralogues of GlVps4 and GlVps46 further underscores the distinct cellular roles of these late-ESCRT paralogues.