Protein Crystallization Hits

Seeding with protein 'crap': Microseed Matrix Screening

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What's the new thing that people are tying out these days? Lots of new methodologies, ranging from low-volume plug-based crystallization (of course) to new crystallization screening matrices for membrane proteins. I've noticed that there's a 'new' seeding method around that has come up in several conversations I've had with protein crystallizers over the past 3 years or so. It's called Microseed Matrix Seeding. Judging from people who try and stick with it, it is my impression is that this seems to be working rather well.

What is Microseed Matrix Seeding in practical terms?

You start with a 'failed' primary protein crystallization tray and:

1. Harvest some or all the precipitated drops, pool them (yes!) and call this seed stock.
2. Spike each drop of a new, secondary crystallization trial with a portion of the seed stock.
3. Obtain crystals from a protein/formulation combination that is different from that you used to create the seed stock with.

The Matrix Microseeding method and its application to yeast cytosine deaminase was first described by Gregory Ireton and Barry Stoddard in:

G. Ireton & B. Stoddard

Microseed matrix screening to improve crystals of yeast cytosine deaminase

Then Alan D'Arcy picked up on this new method and initiated a robotic application for this new protein crystallization seeding method:

Seeding with 'crap'? (mind me - not my own words, but I've heard this very question more than once)

Maybe not. What you see as precipitated material may be not properly characterized crystalline material. For all I know, there could be sub-micrometer sized microcyrstalline protein material mixed in the precipitate. And there's just no way for you to see that. Alternatively, the precipitated protein material itself may form a heterogenous nuclation surface in similar ways that seaweed or horse hair can serve as nuclei for protein crystallization.

A case for Microseed Matrix Screening(?) 

If you you've got many drops with precipitation in it (B), and no crystallization leads whatsoever - why not try give it a try?

Thanks,

Peter