# Subcellular proteomics reveals a blueprint for endosymbiont integration in trypanosomatid Angomonas deanei

## TL;DR

This study maps proteins in the protist Angomonas deanei and its bacterial endosymbiont, revealing how they interact and integrate metabolically.

## Contribution

The study provides a detailed subcellular proteome of Angomonas deanei and its endosymbiont, identifying novel host proteins targeted to the bacterium.

## Key findings

- Over 5,000 host proteins and 400 endosymbiont proteins were localized using subcellular proteomics.
- Novel host-encoded proteins targeted to the endosymbiont were identified and validated experimentally.
- Metabolic interactions were revealed, including energetic links between host glycosomes and acidocalcisomes with the endosymbiont.

## Abstract

The acquisition of endosymbionts is a fundamental process that has driven the evolution of eukaryotes. The tree of life is filled with cases of internalised prokaryotes that have become integrated into their hosts, often forming mutually beneficial relationships. The trypanosomatid Angomonas deanei is one such case, harbouring a single β-proteobacterial endosymbiont. This symbiotic relationship is highly advanced, as evidenced by the identification of host-encoded proteins that are targeted to the bacterium and control its division. To deeper understand this integration, we performed an in-depth subcellular proteomic analysis to determine the compartmental localisation of both host and endosymbiont proteins. Our analysis resolved over 5,000 host proteins and over 400 endosymbiont proteins. We used this rich dataset to identify several novel host-encoded proteins targeted to the bacterium, and validated our predictions using genetic manipulations and microscopy. By mapping the localised enzymatic repertoire, we were able to shed light on metabolic interplay between the two organisms. We confirmed an energetic basis for the previously observed association between the host’s glycosomes and its endosymbiont, and discovered an interaction between the endosymbiont and the host’s acidocalcisomes. This subcellular proteomic dataset provides a comprehensive foundation for future research into the remarkable process of bacterial integration.

The flagellated protist Angomonas deanei harbours a bacterial endosymbiont. Here, Hammond et al. report a high-confidence subcellular proteome, localising 5,796 proteins of the protist and its endosymbiont to various organelles and cell compartments, and identify several host-encoded proteins that are targeted to the bacterium.