Department Colloquium: The influence of geometry beyond equilibrium: How size controls delivery and signaling for cellular organelles

Speaker

Aidan Brown, Toronto Metropolitan University

Abstract

Among their many features, living cells maintain spatial organization and send internal signals to sustain their health and functional capacity. Targeted delivery and clustering of proteins are key to spatial organization and intracellular signaling. This talk will focus on the physical principles that control the delivery of proteins to mitochondria and clustering of proteins on the endoplasmic reticulum, with a significant role for the size of these organelles. Mitochondria, popularly known as powerhouses of the cell, form dynamic tubular networks. I will describe our theoretical work examining how protein translation and mitochondrial geometry combine to drive mRNA association, and thus protein delivery to mitochondria, out of equilibrium and enable distinct mRNA targeting behaviour. I will also explain how small mRNA numbers, combined with mitochondrial size, can control mitochondrial protein concentration fluctuations. I will then examine the dynamics of IRE1 protein clusters on the tubes of the endoplasmic reticulum (ER), an organelle composed of a cell-spanning network sheets and tubes. With a lattice gas model, we find that narrow ER tubes facilitate IRE1 cluster wrapping around the tubes, allowing clusters to grow more rapidly, evaporate more slowly, and remain stable at lower protein concentrations. Overall, geometry in the form of organelle size is an important factor in the nonequilibrium processes of protein delivery and cluster-driven signaling inside living cells.