Building Protein-Based Nanomaterials

Today and tomorrow, we're reporting on presentations at an important conference on Productive Nanosystems: Launching the Technology Roadmap. Chris Phoenix is providing live blog coverage for us...

Next talk: Matthew B. Francis, Department of Chemistry, University of California, Berkeley, is talking about New Synthetic Strategies to Build Protein Based Nanomaterials.

When it's time to add functional molecules to proteins, only a few reactions are used these days. Sometimes the reaction is incompatible with the function you're trying to add. Their group is starting with viral capsids. 180 copies of a simple protein shape self-assemble into an icosahedral capsule (capsid) that's hollow. He wants to attach one type of things to the outside of the capsule, another to the inside of the capsule. So that means you have to attach two different things to each protein, in the right position, so the right things end up on the inside and the outside.

He's got a slide up with lots of chemical reactions, showing how molecules can be joined together. "To remind you why you didn't go into organic chem."

Bacteriophage MS2: affects E.coli, harmless to humans. Easy to grow, high yield. Stable to 60 C. Has 2-nm holes. Can be emptied of RNA by soaking at pH 11.8. Stable from pH 3 to 11. In other words, generally useful.

There's a unique amino acid on the inside of the capsule, and there's a reaction that will attach stuff to it.

They studied what happened to their capsule constructions in a rat in a PET scanner. Found that a small molecule was dumped into the bladder in minutes, but their molecular construction, being a lot bigger, wasn't cleared as quickly.

They've found a way to attach antibodies to other proteins. This is very useful for binding those proteins to whatever the antibody can bind to (almost anything). They built a molecule that'll generate a toxic form of oxygen when exposed to light. (Implication: if the antibody was for cancer cells, you could kill the cells in a very targeted way.)

Tobacco mosaic virus is stable at high temperatures, and can be harvested from tobacco plants in very large quantity. TMV can be broken up into rings. Photosynthetic bacteria use ring-structures to position chromophores (light absorbers) for maximum efficiency. They've attached chromophores to TMV rings, and found that light can be transferred from 38 "donor" to each "acceptor" chromophore. That implies that the construction is defect tolerant. They put other chromophore colors, and got 90% efficiency. Finally, they attached ketones to the outside of the TMV (the chromophore wound up on the inside) and attached gold particles to the keytones. The ultimate goal is to convert the light into a chemical transformation: to turn light into electron transfer.

He closed with a mention of modifying "whole cells" which I assume means attaching stuff to cellular proteins. He showed a slide of cells stuck to a surface in a precise line forming cursive letters.

My summary: This is cool stuff. To the extent that you can build nanoscale stuff out of the virus, that's great. In addition, their approach seems applicable to broader protein engineering. More ways to attach stuff to protein molecules is always useful.

Chris Phoenix

Tags: nanotechnology nanotech nano science technology ethics weblog blog