Presenter: Tyler S. Harmon
Guest Scientist
Max Planck Institute for Physics of Complex Systems 

Topic: Droplets as chemical reaction centers in cells

Over the past decade there has been a surge of interest in the membrane-less organelles.  Showing that their behavior is reminiscent of liquid droplets has brought them into the spotlight in part because it highlights that their behavior can be explored through the lens of polymer physics.  I will highlight two unexpected applications that droplets could be utilized for: the ability for cells to induce droplets to differentiate without changing the major components, and aiding the assembly of large complex through organizing an assembly line. 

 Each class of these droplets can have unique properties and thus perform unique functions for the cell.  The construction and deconstruction of these droplets has been proposed as a mechanism for cell signaling. However, another possibility is that cells might convert an existing type of droplet into multiple coexisting subclasses with different functions to facilitate signaling.  These new organelles would be composed of the same scaffold proteins but recruit different machinery and substrates, thus behaving as distinct subclasses.  These droplets have thus differentiated similar to why cells differentiate.  This can be demonstrated in a minimalistic model based on a phosphatase-kinase competition with a phosphorylation site on the scaffold.

 Large protein complexes are assembled from protein subunits to form a specific structure. Using theory, we propose that assembly into the correct structure could be reliably achieved through an assembly line with a specific sequence of assembly steps.  Using droplet interfaces to position compartment boundaries, we show that an assembly line can be self organized by active droplets.  As a consequence, assembly steps can be arranged spatially so that a specific order of assembly is achieved and incorrect assembly is strongly suppressed.

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America/New_York
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For access to this seminar, please contact Camille Norrell via email: cnorrell@flatironinstitute.org