The determination of whether the crystal structure of a protein is the same as that in solution, and the ability to solve structures of proteins that do not form crystals, are issues that require a marriage of X-ray diffraction crystallography and nuclear magnetic resonance (NMR) spectroscopy. Here is the first solution of an X-ray structure using a previously obtained NMR structure. The differences in the structures for the short, 72-amino acid polypeptide are small but important.

E.T. Baldwin, I.T. Weber, R. St. Charles, J.-C. Xuan, et al., "Crystal structure of interleukin-8: symbiosis of NMR and crystallography," PNAS, 88, 502-6, 15 January 1991. (National Cancer Institute, Frederick and Bethesda, Md.; et al.)

Genetic analysis of amino acid residues needed for proper protein folding (rather than subsequent function) is leading to a series of "patterns." The use of mutants that are temperature-sensitive for folding and secondary mutations that reverse the sensitivity maps...

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