The high-resolution structure of a protein provides a great deal of useful information. It is often a source of insight into the function of an unknown protein; it may also suggest the locations of active sites and provide information about other molecules that interact with the protein. Furthermore, knowledge of a protein’s structure often suggests targets for potential drugs that might interact with the protein. Therefore, one goal of proteomics is to determine the structure of every protein found in a cell.

Two procedures are currently used to solve the structures of complex proteins: (1) X-ray crystallography, in which crystals of the protein are bombarded with X-rays and the diffraction patterns of the X-rays are used to determine the structure (see Chapter 8); and (2) nuclear magnetic resonance (NMR), which provides information on the positions of specific atoms within a molecule by using the magnetic properties of their nuclei.

Both X-ray crystallography and NMR require human intervention at many stages and are too slow for determining the structures of the thousands of proteins that may exist within a cell. Because the structures of hundreds of thousands of proteins are required for studies of the proteome, researchers ultimately hope to be able to predict the structure of a protein from its amino acid sequence. That is not possible at the present time, but the hope is that, if enough high-resolution protein structures are solved, it will be possible in the future to model the structures from the amino acid sequence alone. As scientists work on automated methods that will speed the structural determination of proteins, bioinformaticists are developing better computer programs for predicting protein structure from sequence. TRY PROBLEM 22