ABSTRACT
Determination of the three-dimensional structure of a protein can be considered as one of the most important goals in biochemistry. A variety of experimental methods exist that can be used for analysis of protein structures (described in part II of this book). Most of these techniques are slow, laborious, and expensive. At the same time, massive amounts of protein sequence data are produced by large-scale genome-sequencing projects, and knowing their three-dimensional structures could be very helpful for functional annotation. As we discussed in the Chapter 18, putative functions can sometimes be assigned to newly identied genes by sequence comparison methods. However, the threedimensional structure of a protein rather than its amino-acid sequence carries out the biochemical function of a protein. Therefore, a tentative function can be assigned to a hypothetical protein by comparing its structure to previously solved structures of proteins with assigned functions. As an example, the importance of structural similarities between two functionally related proteins can be seen by comparing hemoglobin and myoglobin, which are both oxygen carriers. The solved three-dimensional structures of the human α-globin and myoglobin are very similar, but their amino-acid sequences are different (26% identity, 38% similarity; see Chapter 18, Figure 18.1).
