Fig. 4.

Effect of substrates on the gradients of coupled water motions. (A) Changes in hydration dynamics on Michaelis complex formation. Shown are the averaged hydrogen bond lifetimes τ_HB of bulk water (red line; distance to closest protein atom > 10 Å), water molecules solvating MT1-MMP (magenta line; distance to closest enzyme atom < 3 Å), and water solvating the zinc ion (distance to catalytic zinc ion < 6 Å) in the unbound MMP–triple-helical substrate system (purple line), the MMP–single-stranded substrate system (blue line), and the MMP–triple-helical substrate system (cyan line). (B) A gradient of water motions [from retarded water molecules (cyan) to bulk (red)] is detected in the unbound MT1-MMP when the substrates are at a distance d of ∼7 Å from the zinc ion. When the substrates approach closer to the zinc ion (d ∼ 4.9 Å), an additional decrease in the water HB lifetime at the active site for both substrates is observed. The gradient of water motions depends on the substrate: τ_HB is steeper when the MT1-MMP is bound to the triple-helical substrate (Right) than when it is bound to the single-stranded substrate (Center).