# 'Structure and function of the R-body, a piston-like nanomachine

> **NIH NIH R01** · UNIVERSITY OF WASHINGTON · 2020 · $330,438

## Abstract

Project Summary
R-bodies are self-assembling protein polymers from bacterial ensymbionts of 'killer' Paramecium strains that
confer to the host the ability to kill competing strains. The tightly coiled sub-micron sized R-body undergoes a
massive pH induced conformational change into elongated rods tens of microns long, generating forces
sufficient to rupture biological membranes. Purified recombinant R-bodies can undergo many successive
rounds of piston-like extension and contraction using only the chemical energy from pH change. These robust
nanomachines have enormous potential for biotechnological and therapeutic applications. Their ability to
behave as sensitive switches and to do work on biological structures can be adapted for many functions - they
have, for example, been proposed as systems for phagosomal delivery of bioactive molecules in a way that
would mimic their biological function. The ability to tune R-body behavior was recently demonstrated by a
panel of point mutants that alter the triggering pH for extension. However, the lack of detailed molecular
understanding of their assembly and the mechanism of the pH-sensitive piston-like extension are major
roadblocks to developing R-bodies for novel applications. This proposal aims to determine the molecular
architecture of R-bodies using a hybrid structural approach, and to measure their biophysical properties using
optical trapping force measurements. Visualizing the three-dimensional structure of R-bodies in coiled and
extended states will allow us to define the molecular mechanism of their piston-like behavior, laying the
groundwork for tuning the structures to new functions.

## Key facts

- **NIH application ID:** 9951068
- **Project number:** 5R01GM127648-03
- **Recipient organization:** UNIVERSITY OF WASHINGTON
- **Principal Investigator:** Justin M Kollman
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2020
- **Award amount:** $330,438
- **Award type:** 5
- **Project period:** 2018-06-01 → 2022-05-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/9951068

## Citation

> US National Institutes of Health, RePORTER application 9951068, 'Structure and function of the R-body, a piston-like nanomachine (5R01GM127648-03). Retrieved via AI Analytics 2026-05-23 from https://api.ai-analytics.org/grant/nih/9951068. Licensed CC0.

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