Tissue inhibitor of metalloproteinases-1 undergoes microsecond to millisecond motions at sites of matrix metalloproteinase-induced fit

The N-terminal, matrix metalloproteinase (MMP)-inhibitory fragment of recom binant, human tissue inhibitor of metalloproteinases (TIMP-1) exhibits vari ed backbone dynamics and rigidity. Most striking is the presence of chemica l exchange in the MMP-binding ridge reported to undergo conformational chan ge upon MMP binding. Conformational exchange fluctuations in microseconds t o milliseconds map to the sites of MMP-induced fit at residues Val29 throug h Leu34 of the AB loop and to the Ala65 and Cys70 "hinges" of the CD loop o f TIMP-1. Slow chemical exchange is also present at the type I turn of the EF loop at the base of the MMP-binding ridge. These functional slow motions and other fast internal motions are evident from backbone N-15 spin relaxa tion at 500 and 750 MHz, whether interpreted by the model-free formalism wi th axial diffusion anisotropy or by the reduced spectral density approach. The conformational exchange is confirmed by its deviation from the trend be tween R-2 and the cross-correlation rate eta. The magnetic field dependence indicates that the chemical exchange broadening in the AB and CD loops is fast on the time-scale of chemical shift differences, The conformational ex change rates for most of these exchanging residues, which can closely appro ach MMP, appear to be a few thousand to several thousand per second. The sl ow dynamics of the TIMP-1 AB loop contrast the picosecond to nanosecond dyn amics reported in the longer TIMP-2 AB loop. (C) 2000 Academic Press.