Deterministic Early Endosomal Maturation Driven By Eea1 Noise Suppression
Endosomal trafficking in single cells is built of generation of membrane vesicles, their motor protein mediated transport, morphological alterations such as tubulation, fusion and fission, and dynamic maintenance of various identities, which is defined by the lipid composition and localization of specific proteins on them. Endosomal maturation is a major process in endosomal trafficking in which endosomes shed one specific protein and acquire another, resulting in an identity change. Individual processes that build up endosomal trafficking, including conversions, are interlinked and are inherently stochastic. While the general biochemical interactions have been well described, how all the events come together to overcome the inherent noise and stochasticity is much less explored. Here, capitalising on the rapid volumetric imaging capability of Lattice-light sheet, we capture whole-cell volumes, enabling post-acquisition analysis of all conversion events as well as other dynamic characteristics. We show that early endosome maturation is driven by endosomal collision-induced conversions. Furthermore, using live-cell Förster Resonance Energy Transfer, we demonstrate that this is underpinned by cyclical conformational changes in EEA1, which promotes the biochemical maturation of these vesicles through its asymmetric binding capacity and clustering on the endosomal membranes. Using simulations, we recapture the experimentally observed characteristics in the reaction scheme and the activity of EEA1. Based on these experiments, we describe an EEA1-dependent mechanism that enables deterministic outcomes in ensemble endosomal conversions in an otherwise stochastic system.