Ectoine is one of the most common compatible Solutes found in halophilic bacteria, and has ail effect to introduce a tolerance to high salt concentration or high temperature. By analyzing l ns molecular dynamics Simulations at 370 K, we have shown that. in the ectoine aqueous Solution, the water diffusion slows down around a protein (chymotrypsin inhibitor 2 (C12)), keeping the protein hydration structure essentially Unchanged. It is concluded that the slowdown of water diffusion around the backbone amide protons must be one of the decisive factors in reducing the exchange rate of the backbone amide protons, whose reduction is experimentally believed closely related to the tolerance effect. (C) 2004 Elsevier B.V. All rights reserved.