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

## TL;DR

This study explores the different roles of ESCRT proteins in Giardia lamblia, showing they have unique functions during cell transformation and membrane changes.

## Contribution

The paper reveals functional divergence among ESCRT paralogues in Giardia through distinct subcellular localization and selective protein interactions.

## Key findings

- ESCRT paralogues in Giardia show non-overlapping subcellular distributions and distinct interactions.
- GlIst1 selectively interacts with GlVps4b and GlVps46b, highlighting specialized roles.
- ESCRT components redistribute during encystation, suggesting involvement in morphological transitions.

## Abstract

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.

Giardia lamblia, a unicellular protozoan parasite, manifests in two morphologically distinct forms- trophozoites and cysts. Transformation between these forms is essential for the organism’s survival both within the host and without. It requires extensive membrane remodeling, which is likely to involve the Endosomal Sorting Complex Required for Transport (ESCRT) complexes, as this machinery is known to participate in both prokaryotic and eukaryotic membrane remodeling events. Giardia was known to encode multiple paralogs of the late-ESCRT components, GlVps4 and GlVps46, raising the possibility of them performing nonredundant functions. Our study indicates functional divergence of the paralogs by showing their nonoverlapping cellular distribution and also documenting selective interactions between them. The redistribution of these paralogs to sites of membrane deformation during encystation, along with regions of microtubule enrichment, indicates that they are likely to contribute to the stage transition process. Also, observed Giardia-specific interactions within ESCRTs opens new therapeutic avenues.