Saturday, October 21, 2006

Intrinsically unstructured proteins

It's long been the conventional wisdom that proteins have rigidly fixed shapes which are crucial to their function – at least those proteins which actually have important functions. But now, apparently, not so much:

First Major Study Of Mammalian 'Disorderly' Proteins
Unlike the classic description of proteins described in science textbooks, IUPs are not completely locked into rigid, 3-D shapes that determine their function in the cell. Instead, IUPs have varying amounts of flexibility within their sometimes spaghetti-like structures that is critical for function. For example, one protein named p27 initially looks like a Slinky™ toy. However, when p27 goes to work, it puts a vise-like grip on an enzyme that otherwise would promote uncontrolled cell division.

The St. Jude team developed a technique that uses heat to isolate IUPs in large, purified quantities from extracts of a standard type of cultured mouse cells called NIH3T3 fibroblasts. The IUPs were resistant to the heat, unlike more structured proteins, which fell apart. Based on these studies, the investigators were able to classify all proteins into one of three categories: IUPs; intrinsically folded proteins (IFPs, i.e., fully folded into specific shapes); or mixed ordered or disordered proteins (MPs), which have both structured and unstructured parts.

The point isn't that protein scientists have been wrong all this time, so much as that nature will often be able to find a use for building blocks in order to take advantage of varying characteristics that are available.

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