Date of Award

Spring 2021

Project Type

Dissertation

Program or Major

Biochemistry

Degree Name

Doctor of Philosophy

First Advisor

Krisztina Varga

Second Advisor

Xuanmao Chen

Third Advisor

Rick Cote

Abstract

The polar organizing protein Z (PopZ) is an intrinsically disordered protein from Caulobacter crescentus that is necessary for the formation of three-dimensional microdomains at the cell poles, where it functions as a hub protein that recruits multiple regulatory proteins. Although a large portion of the protein is predicted to be disordered, PopZ can self-assemble into polymeric superstructure scaffolds that directly bind to at least ten different proteins. Here, we report the solution NMR structure of PopZΔ134–177, a truncated variant of PopZ that does not self-assemble but retains the ability to interact with heterologous proteins. We show that the unbound form of PopZΔ134–177 is unstructured in solution, with the exception of a small amphipathic α-helix encompassing residues M10-I17, which is included within a highly conserved region near the N-terminus. In applying NMR techniques to map the interactions between PopZΔ134–177 and one of its binding partners, RcdA, we find that the α-helix and neighboring residues extending to position E23 serve as the core of the binding motif. Consistent with this, a point mutation at position I17 perturbs the binding region and severely inhibits interaction with RcdA. Our results show that a partially structured Molecular Recognition Feature (MoRF) within an intrinsically disordered domain of PopZ contributes to the assembly of polar microdomains, revealing a structural basis for complex network assembly in Alphaproteobacteria that is analogous to those formed by intrinsically disordered hub proteins in other kingdoms.

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