Crystallizing proteins in cell

A3 tbcatbTrying days and nights to crystallize your protein in vitro?  Stop it right now! Maybe the best way to solve its structure is to… do it in cell? And destroy it?
Since long time ago structural biologists have been using x-ray crystallography as a universal method for solving structures of proteins. In this method, proteins are crystallized and x-ray beam is applied to them. The beam meets protein and is diffracted. Finally, pattern of diffraction is used to obtain detailed structure.  However, it poses some problems difficult to overcome. For instance, since x-rays are destructive to proteins, you have to obtain relatively huge amounts of it. And it became a real art.

 

To overcome this problem, group leaded by Henry Chapman from Hamburg apply slightly different approach – they use free electron lasers to generate incredibly fast femtosecond x-rays (femto means 10-15). You may ask “woudn’t such high-energy radiation destroy protein?”. And well, it will but relatively much later after pattern of diffraction will be recorded. X-rays are so fast here that the protein won’t have enough time for being destroyed. So surprising, isn’t it?

Thanks to femto, group can solve structures of proteins that can’t be crystallized in large amounts. And here they came up with another innovations. If size is not a limit now, why don’t crystallize protein… in cell in vivo? And they managed to do with Cathepsin B which they overexpressed in T. brucei! Here you can see SEM picture of single crystal (picture was taken
from here.):

A3 krysztal w komórce

Femtosecond Crystallography

Paper in Science about crystallizing Cathepsin B

Prof. Chapman’s Group

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