BIOSYNTHESIS OF THE 17-KDA AND 27-KDA N-T ERMINAL FRAGMENTS OF ELONGATION-FACTOR EF-2 AND THEIR CONFORMATION IN SOLUTION

N-Terminal fragments of the rat liver elongation factor EF-2 containin g 162 (17 kDa) and 244 (27 kDa) amino acid residues of 857 (95 kDa) re sidues of the native protein were synthesized in E. coli cells and in a wheat germ cell-free translation system, and their conformations wer e studied. Both fragments were synthesized as inclusion bodies (nonspe cific molecular aggregates), The conformations of the fragments in a s olution were studied at neutral pH values by CD, fluorescence spectros copy, scanning microcalorimetry, viscosimetry, gel-filtration, limited proteolysis, and interaction with monospecific anti-EF-2 antibodies a nd GroEL/ES molecular chaperon. Under nondenaturing conditions, both f ragments existed in a solution as associates within a broad range of m olecular masses, contained a considerable amount of elements of the in tramolecular secondary structure, and represented globules without rig id tertiary structure (molten globules). A rigid tertiary structure wa s not formed even after the interaction of the fragments with the GroE L/ES molecular chaperone, thus indicating that the C-terminal fragment is essential for the formation of the rigid tertiary structure, Both fragments contained conformational antigenic determinants similar to t hose in the whole protein; i.e., despite the absence of the rigid tert iary structure, the fragments contained elements whose structure was s imilar to that of the corresponding regions in the whole protein.