Front bifurcation in a self-organizing kinase/phosphatase system capable of membrane trafficking

Biological systems self-organize into complex functional spatiotemporal structures. Here, we study the rich dynamical patterns generated by the proteins MavQ and SidP of the intracellular bacterial pathogen Legionella pneumophila. In vivo after infection, the pair exhibits traveling waves on the host ER membrane, remodeling membranes and inducing rapid lipid turnover. When the system is reconstituted in vitro, an even richer set of patterns emerges. To understand this, we develop a continuum theoretical model describing the interaction between MavQ, SidP, and phosphatidylinositol lipids which can be phosphorylated and dephosphorylated by the proteins. We identify a parameter regime where the system segregates into high-MavQ and low-MavQ regions. The front separating the two regions can undergo an Ising-Bloch bifurcation, which generates a variety of dynamical patterns such as spiral waves, spiral turbulence, and breathing droplets. By combining theory and experiments, our work provides new insights into membrane remodeling by Legionella effector proteins and establishes a promising new minimal model system for studying protein-lipid self-organization.