Host-symbiont interactions in Angomonas deanei include the evolution of a host-derived dynamin ring around the endosymbiont division site

The trypanosomatid Angomonas deanei is a model to study endosymbiosis. Each cell contains a single β-proteobacterial endosymbiont that divides at a defined point in the host cell cycle and contributes essential metabolites to the host metabolism. Additionally, one endosymbiont gene, encoding an ornithine cyclodeaminase (OCD), was transferred by endosymbiotic gene transfer (EGT) to the nucleus. However, the molecular mechanisms mediating the intricate host/symbiont interactions are largely unexplored. Here, we used protein mass spectrometry to identify nucleus-encoded proteins that co-purify with the endosymbiont. Expression of fluorescent fusion constructs of these proteins in A. deanei confirmed seven host proteins to be recruited to specific sites within the endosymbiont. These endosymbiont-targeted proteins (ETPs) include two proteins annotated as dynamin-like protein and peptidoglycan hydrolase that form a ring-shaped structure around the endosymbiont division site that remarkably resembles organellar division machineries. The EGT-derived OCD was not among the ETPs, but instead localizes to the glycosome, likely enabling proline production in the glycosome. We hypothesize that recalibration of the metabolic capacity of the glycosomes that are closely associated with the endosymbiont helps to supply the endosymbiont with metabolites it is auxotrophic for and thus supports the integration of host and endosymbiont metabolic networks. Hence, scrutiny of endosymbiosis-induced protein re-localization patterns in A. deanei yielded profound insights into how an endosymbiotic relationship can stabilize and deepen over time far beyond the level of metabolite exchange.