# Self-assembly and function of bacterial microcompartments

> **NIH NIH R01** · UNIVERSITY OF CALIFORNIA BERKELEY · 2020 · $298,579

## Abstract

Bacterial cells possess significantly more ultrastructural organization than is typically appreciated. One
of the most striking examples of this are bacterial microcompartments (BMCs), large (i.e. 100+ nm)
proteinaceous complexes that encapsulate cargo enzymes catalyzing a short metabolic pathway within
a capsid-like shell. BMCs enable metabolism incompatible with their host and this functional advantage
is borne out in their pervasiveness. 20-30% of bacterial genomes possess BMC-like proteins. Despite
this prevalence, only a handful of BMCs are characterized. One of the most intriguing open questions
surrounding BMCs is how a mature functional complex emerges from only protein-protein interactions.
Specifically, the mechanism of assembly, cargo ordering and stoichiometry, and the robustness, shape,
and size of the mature complex cannot be explained from the current qualitative knowledge of known
protein interactions. The goal of our work is to use mechanistic biochemical approaches in order to
understand the in vivo self-assembly and function of the BMC known as the α-carboxysome (α-CB). The
α-CB facilitates autotrophic growth in many bacteria and was the first BMC to be characterized due to its
robustness and ease of biochemical analysis. It is therefore an excellent model system to answer these
open questions. Preliminary data indicates that a protein known as CsoS2 is essential for α-CB formation
and may be the hub of an interaction network driving self-assembly. We propose to use biochemical and
biophysical tools in order to both map the molecular determinants of these interactions and quantitatively
understand how multivalency controls assembly. CsoS2 is also an intrinsically disordered protein and
possesses numerous repetitive sequence elements. Preliminary data indicates these regions of CsoS2
play an important role in determining α-CB size. Intrinsically disordered proteins are known to participate
in an organizing role in eukaryotes, but are largely uncharacterized in prokaryotes. We therefore propose
a series of experiments to understand the significance of disorder to CsoS2 function and how its repetitive
elements are involved in determining the outcome of the assembly process. Finally, it has long been
postulated that BMCs act like an organelle and possess a chemical environment that is distinct from the
cytosol. This hypothesis is supported by circumstantial data but has never been directly measured
biochemically due to experimental challenges. Here we proposed a series of experiments to make this
measurement ex vivo by determining whether the α-CB naturally possesses an oxidative lumen due to
the action of its protein shell. We will additionally determine to what extent the chemistry of the lumen
affects the self-assembly process. If successful, these experiments will provide novel mechanistic insight
into how BMCs assemble and function, and more broadly, the interplay between bacterial ultrastructure
and bacterial physiology.

## Key facts

- **NIH application ID:** 9984452
- **Project number:** 5R01GM129241-03
- **Recipient organization:** UNIVERSITY OF CALIFORNIA BERKELEY
- **Principal Investigator:** David Frank Savage
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2020
- **Award amount:** $298,579
- **Award type:** 5
- **Project period:** 2018-09-15 → 2022-07-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/9984452

## Citation

> US National Institutes of Health, RePORTER application 9984452, Self-assembly and function of bacterial microcompartments (5R01GM129241-03). Retrieved via AI Analytics 2026-05-27 from https://api.ai-analytics.org/grant/nih/9984452. Licensed CC0.

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