ABSTRACT
New guanine nucleotide-binding (GNB) proteins keep on being discovered continuously and the number of individual members of this family of proteins may be 50 to 100 for a higher organism. In order to understand their function and mechanism of action, it is important to get a detailed description of the three-dimensional structure of these proteins down to the atomic level. This has been achieved for p21, the product of the ras protooncogene. It has enabled us to understand the basic features of this molecule whose general function is as a molecular switch. Although the three-dimensional structure of no other GNB protein except bacterial elongation factor Tu (EF-Tu) has been determined, albeit at lower resolution, the results of the structure determination have implications for other GNB proteins as well.
