Increased backbone mobility in beta-barrel enhances entropy gain driving binding of N-TIMP-1 to MMP-3.
The high-affinity inhibition of stromelysin 1 (MMP-3) by tissue inhibitor of metalloproteinases 1 (TIMP-1) helps control tissue remodeling and tumor development. The interaction of N-TIMP-1 with the catalytic domain of MMP-3 has been investigated by titration calorimetry and 15N NMR. Their unfavorable enthalpy of binding of +6.5 kcal mol(-1) is unusual among protein-protein associations, deviates from structure-based prediction, and is compensated by a net entropy increase providing at least 18 kcal mol(-1) of favorable free energy of binding at a 1M reference state. The small heat capacity of binding agrees well with the heat capacity predicted from 65% of the surface buried on binding being polar, and suggests that the hydrophobic effect can account for only part of the entropy of binding. Using NMR, binding-induced changes in the backbone of N-TIMP-1 were checked as one possible source of conformational entropy changes. MMP binding slightly increases rigidity in some contact sites in TIMP-1 but increases mobility remotely in the otherwise rigid beta-barrel core of N-TIMP-1, increasing 15N relaxation evidence of pico- to nanosecond and micro- to millisecond fluctuations of beta-strands A-F. Residual dipolar couplings suggest dynamic deviations from X-ray coordinates of the complex. These suggest that the beta-barrel has small backbone conformational fluctuations, while segments of strands betaB, betaE and betaF might experience fluctuations only in their backbone environment. This is a distinctive example of affinity between two well-structured proteins being enhanced by increased conformational entropy in the reservoir of a folding core.
Arumugam
S
S
Department of Biochemistry, University of Missouri, 117 Schweitzer Hall, Columbia, MO 65211, USA.
Gao
Guanghua
G
Patton
Brian L
BL
Semenchenko
Valentyna
V
Brew
Keith
K
Van Doren
Steven R
SR
D055592:Biophysical Phenomena; D001703:Biophysics; D002151:Calorimetry; D019277:Entropy; D006358:Hot Temperature; D006801:Humans; D009682:Magnetic Resonance Spectroscopy; D019278:Matrix Metalloproteinase 3 / Q000737:chemistry* / Q000378:metabolism; D008958:Models, Molecular; D011485:Protein Binding; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D013696:Temperature; D013816:Thermodynamics; D019715:Tissue Inhibitor of Metalloproteinase-1 / Q000737:chemistry* / Q000378:metabolism
D019715:Tissue Inhibitor of Metalloproteinase-1; D019278:Matrix Metalloproteinase 3