Crystallization, X-ray analysis, and the tertiary structure

The crystallization of native elongation factor Tu isolated from bacterial cells, i.e. in complex with GDP, proved to be difficult. Useful crystals for X-ray structure analyses could be obtained only from a partially trypsinized E. coli EF-Tu GDP missing a part of the L2 region (amino acid residues 45-58 E. coli numbering). Through laborious efforts of several crystallographic groups, the structure of the partially proteolyzed E. coli EF-Tu GDP has been determined up to 2.5 A resolution [56]. 

The structure of EF-Tu in the active GTP form, namely that of EF-Tu GppNHp from T thermophilus, was determined up to 1.7 A resolution [1]. The EF-Tu structures in GDP and GTP bound forms can now be compared (Fig. 19.12). However, we still have to keep in 

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