Biochemical and structural studies of the tetragonal crystalline modification of the Escherichia coli elongation factor Tu.

The tetragonal crystalline form of the trypsin-treated Escherichia coli protein elongation factor Tu has been analyzed by biochemical and x-ray crystallographic techniques. The crystals contain two tightly associated polypeptide fragments of molecular weight 36,000 and 6,500 which represent 97% of the native enzyme. The crystals do not contain a short internal polypeptide fragment of 14 amino acids which dissociates from the native enzyme following mild trypsin digestion. The short fragment has been implicated in the aminoacyl-tRNA binding function and its location has been determined. The structure of the modified enzyme in the P4(3)2(1)2 crystal form has been determined to 5 A resolution by x-ray diffraction methods. The protein consists of two domains: the larger domain exhibits considerable alpha helical characteristics and the smaller domain has no identifiable secondary structural features. The relationship between the double domain structure of the enzyme and its biochemical properties is discussed.