Beneath the surface of ‘surface densities’

October 26, 2021

By Jim Shelton

In a new study in the Proceedings of the National Academy of Sciences, Yale researchers Mason Rouches and Benjamin Machta, as well as University of Michigan researcher Sarah Veatch, look at a specific way that cell proteins signal each other.

Called “phase separation of proteins,” it is an active area of current research and refers to the way proteins sometimes separate into two distinct phases — much like the way oil and water separate after they are mixed.

We examine what we term ‘surface densities’ — liquid-like assemblies of proteins found exclusively on the cell membrane,” said Rouches, a graduate student in molecular biophysics and biochemistry at Yale. “Our focus is on the subclass of proteins that phase-separate at cell membranes, often aiding in signaling.”

Rouches and Machta argue that these surface densities are prewet — a technical term used in physics. A prewet ‘phase’ would be, for example, a molecularly thin, two-dimensional film of liquid that forms on the surface of a system whose bulk is in a three-dimensional gas phase.

In this case, proteins are stabilized as droplet-like films at the membrane surface. “We find that phase-separation in the membrane encourages the phase separation of proteins at the cell surface, and that proteins likewise encourage phase separation of lipids in the membrane, reinforcing each other in a single surface phase,” said Machta, an assistant professor of physics in Yale’s Faculty of Arts and Sciences and a member of the Systems Biology Institute at West Campus.

The research offers insight into mechanisms of signaling cluster formation — for example, the clusters that form in T-cells upon engagement with a foreign antigen — and of long-lived protein assemblies found in the synapses of neurons and other cell types.

This article was originally published as part of Yale News’ “Insights & Outcomes” for October 25, 2021.
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