Fig. 2.

Methyl TROSY heteronuclear multiple quantum correlation spectra of U-[¹⁵N,²H], Ile δ1-[¹³C,¹H] ClpP protease (300 kDa). (a) Spectrum of WT ClpP at 0.5°C. The molecular tumbling time is predicted to be >400 ns (14). The upper boxed area is enlarged in b, and the lower boxed area is enlarged in c. Spectra of the ClpP I149V and I151L mutants are consistent with both isoleucines adopting at least two distinct conformations. The dotted circles indicate the positions of cross-peaks that are eliminated by either the I149V or I151L mutation. Note the different line widths for correlations derived from the two states, indicating a difference in internal mobility for state S (slowly relaxing) and F (fast relaxing). (b) Methyl TROSY spectra of WT ClpP showing increased exchange between states F and S as a function of temperature. (c) Representative correlations from nonexchanging Ile residues.