Evan Sayer

Evan Sayer

“The Effects of Scaffolding Polymers on Microcompartment Size”

Evan Sayer, Farri Mohajerani, Michael F. Hagan
Brandeis / Biological Physics and Mathematics
Hosted by Hagan's Lab


Bacterial microcompartments, or BMCs, are protein shells bacteria use to encapsulate collections of enzymes. Attempts have been made to reengineer BMCs to target new enzymes, with goals such as affecting the function of bacteria and delivering drugs to humans. The factors that control BMC assembly and the size of the resulting shells are not fully understood, limiting our understanding of cell biology and ability to reengineer BMCs. One such factor is scaffolding proteins, long polypeptides that drive aggregation of cargo and recruit shell subunits.

To further our understanding, we computationally simulated BMC assembly and studied the effects of scaffolding proteins, modeled as polymers of variable length, on the ability of shells to assemble and their resulting size. We first simulated shell formation in the absence of cargo and polymers to establish the size of empty shells resulting from the intrinsic curvature of the simulated hexamers. We then performed simulations in which we varied polymer lengths, as well as the interaction strengths of polymer-cargo, polymer-hexamer and hexamer-hexamer contacts.

We found that shell assembly occurred by different pathways depending on whether or not the polymer-cargo interaction strength was large enough to drive phase separation of polymer-cargo complexes. For both types of pathways, short polymers caused shells to become smaller than the empty shells, while long polymers caused them to become larger, meaning that polymer length is a key factor controlling shell size. However, the phase-separating polymer-cargo complexes allowed complete shells to form over a wider range of interaction strengths than the non-phase-separating cases, and the largest simulated microcompartments assembled around phase-separating polymer-cargo complexes.


SMURF (Summer MRSEC Undergrad Research Fellowship)