Flexibility and ligand exchange in a buried cavity mutant of T4 lysozyme studied by multinuclear NMR

The Leu99-->Ala mutant of T4 lysozyme contains a large internal cavity in t he core of its C-terminal domain that is capable of reversibly binding smal l hydrophobic compounds. Although the cavity is completely buried, molecule s such as benzene or xenon can exchange rapidly in and out. The dynamics of the unliganded protein have been compared to the wild-type protein by meas uring the NMR spin relaxation rates of backbone amide and side chain methyl nuclei. Many residues surrounding the cavity were found to be affected by a chemical exchange process with a rate of 1500 +/- 200 s(-1), which is que nched upon addition of saturating amounts of the ligand xenon. The relation ship between the structure, dynamics, and energetics of the T4 lysozyme mut ant is discussed.