CCB Colloquium: Benjamin B. Machta

Presenter:
Dr. Benjamin B. Machta, Ph.D.
Assistant Professor of Physics
Yale University

Title: Surface densities prewet a nearly critical membrane.

Abstract: Proteins and nucleic acids can phase separate into three-dimensional liquid droplets in the cytoplasm and nucleus and the plasma membrane appears tuned close to a two-dimensional liquid-liquid critical point. In some examples, cytoplasmic proteins aggregate at plasma membrane domains, with functional roles in forming the post-synaptic density and diverse signaling clusters. I’ll argue that these surface densities are a novel phase reminiscent of pre-wetting, in which a molecularly thin three-dimensional liquid forms on a usually solid surface. However, in surface densities, the solid surface is replaced by a membrane with an independent propensity to phase separate. Using lattice simulations and a minimal Landau theory we have shown that proximity to criticality in the membrane dramatically increases the parameter regime in which a pre-wetting-like transition occurs, leading to a broad region where coexisting surface phases can form.

I will also discuss recent work done in collaboration with the Emonet lab investigating the information efficiency of E. coli chemotaxis. E. coli must acquire and use information about their environment in order to climb gradients, but it is unclear if information quantitatively limits their performance. To address this we first derive a theoretical bound that relates a minimum information rate to a given performance on gradient climbing. Next, we measured the information rate at an intermediate point of the chemotactic pathway, as well as climbing speeds in shallow gradients. We find that E. coli climb gradients at speeds near the limit allowed by our theoretical bound – E. coli chemotaxis is information limited.