Tuesday, January 22, 2008

GroEL-Dependent Proteins Are Mostly Small

R. John Ellis (Nature 2006 442:360) makes the following observation(s): "About 85 different proteins of the bacterium Escherichia coli are thought to require encapsulation inside GroEL–GroES to fold correctly. Of these, 60% are 30–50 kilodaltons in size, and only 14% are greater than 50 kDa in size. The cage of GroEL–GroES measures 80 times 85 Angstroms, sufficient in principle to house proteins up to 70 kDa. However, the available volume is somewhat less, owing to the presence of 23 amino acids at the end of each GroEL subunit. Removal of these tails does not affect the basic mechanism, so they provide a way of changing the size of the cage."

This is interesting in two respects. It is interesting that so few E. coli proteins (only 85) are thought to require GroEL assistance in folding. It's also interesting that GroEL-assisted proteins are mostly small to medium-sized, because one would imagine that small proteins would have simpler folding requirements than large proteins. But on the other hand, the E. coli proteins that require GroEL-assist are (evidently) exceptional in some way.

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