Apparatus for exporting DNA
Secretion System Core Complex”
R Fronzes, et al., Science,
323: 266-268 (2009).
Science recently reported a research advance linked to a series of topics I’ve covered:
- Self-assembled systems
- George Church’s roadmap for radically lowering the cost of DNA
- Structural DNA nanotechnology for modular molecular composite nanosystems
- Cryo-electron microscopy for visualizing large self-assembled structures
The advance is an improved structural map of the core of the self-assembled protein machinery that some bacteria use to export DNA from their cells: A type IV secretion apparatus of the kind that plays a key role in George Church’s roadmap toward making the products of structural DNA nanotechnology cheap enough for widespread use.
Today, DNA is often sold in tiny quantities at dollars per microgram, and “low cost” means thousands of dollars per gram. For products based on structural DNA nanotechnology, costs in this range would limit applications to low-mass, high value uses (for example, sensors, nanoelectronics, catalysts, and thin-film coatings).
George Church, however, has outlined a “Low-Cost DNA Production Roadmap”, aiming to make DNA an affordable industrial biopolymer (like various proteins and polyesters) with a production cost in the dollars-per-kilogram range. This cost reduction — roughly a factor of a million — radically changes the prospects for structural DNA nanotechnology, and from the perspective of researchers aiming to develop practical applications, it immediately expands the scope of what can be considered practical.
To accomplish this, George proposes to engineer bacteria with two important features:
- Upgraded metabolic pathways for synthesizing DNA monomers, and
- A mechanism for secreting the DNA product into the growth medium.
Secretion of DNA prevents it from accumulating in the bacterial cells; this enables them to produce more and allows DNA to be collected by simple means, without first destroying the cells. A type IV secretion apparatus of the necessary kind is found in various gram-negative bacteria. Used as a building block for synthetic biology, it can provide a selective, membrane-spanning portal through which cells deliver designer DNA for convenient harvesting and use.
