Physics Colloquium - Professor Sarah L. Keller
March 25, 2019 - 3:00pm to 4:00pm
Marcus Nano Building
Conference Rooms 1116-1118
University of Washington, Seattle
For decades, scientists have argued about how living cell membranes acquire and maintain regions enriched in particular lipid and protein types. One of the more contentious theories has been that lipids and proteins spontaneously phase separate within the plane of the membrane to create liquid regions that differ in their composition. Physicists have long observed this type of demixing in simple artificial membranes. Clear identification of the same transition in a living biological system had previously been elusive. We addressed this challenge by directly imaging micron-scale membrane domains of yeast organelles both in vivo and cell-free, and we found that large-scale membrane organization in living cells under physiologically relevant conditions can be controlled by tuning a single thermodynamic parameter.
Of course, our observation of micron-scale phases in vacuole membranes does not disprove the popular proposal that other membranes may be heterogeneous on sub-micron length scales. This leads to the interesting question of what would happen if domains became very small – would they cease to colocalize across the two faces of the membrane, hindering signal transduction? This question led to the first measurement of the interleaflet coupling parameter. Our value confirms one prediction, rules out others, and sets a lower bound on domain sizes that result in colocalization.