A small-angle X-ray scattering study of the complex formation between elongation factor Tu . GTP and valyl-tRNA Val I...

The complex formation between elongation factor Tu (EF-Tu) . GTP and valyl-tRNA Val 1 has been investigated using the small-angle X-ray scattering titration technique. The main species observed is a 1:1 complex with a stability constant log K greater than or equal to 6. The corresponding interaction between EF-Tu . GTP and non-aminoacylated tRNA appears to be much weaker with an estimated log K approximately equal to 4. The radius of gyration determined for the EF-Tu . GTP -- valyl-tRNA Val 1 complex is larger (R = 3.6 nm) than that of EF-Tu . GTP (R = 2.5 nm). Likewise, the maximum distance within this complex is larger (Dmax = 12.5 nm) than the one within EF-Tu . GTP (Dmax = 8.5 nm). These data as well as the p(r) curve are consistent with a multiellipsoid model for the complex. From this model it is indicated that the acceptor stem of tRNA is attached to EF-Tu and that the anticodon stem and loop protrude into the solution.