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Published June 1, 2006 | Supplemental Material
Journal Article Open

Ultrafast Solvation Dynamics of Human Serum Albumin: Correlations with Conformational Transitions and Site-Selected Recognition


Human serum albumin, the most abundant protein found in blood plasma, transports a great variety of ligands in the circulatory system and undergoes reversible conformational transitions over a wide range of pH values. We report here our systematic studies of solvation dynamics and local rigidity in these conformations using a single intrinsic tryptophan (W214) residue as a local molecular probe. With femtosecond resolution, we observed a robust bimodal distribution of time scales for all conformational isomers. The initial solvation occurs in several picoseconds, representing the local librational/rotational motions, followed by the dynamics, in the tens to hundreds of picoseconds, which result from the more bonded water in the tryptophan crevice. Under the physiological condition of neutral pH, we measured ∼100 ps for the decay of the solvation correlation function and observed a large wobbling motion at the binding site that is deeply buried in a crevice, revealing the softness of the binding pocket and the large plasticity of the native structure. At acidic pH, the albumin molecule transforms to an extended conformation with a large charge distribution at the surface, and a similar temporal behavior was observed. However, at the basic pH, the protein opens the crevice and tightens its globular structure, and we observed significantly faster dynamics, 25−45 ps. These changes in the solvation dynamics are correlated with the conformational transitions and related to their structural integrity.

Additional Information

© 2006 American Chemical Society. Received: October 19, 2005; In Final Form: January 17, 2006. Publication Date (Web): April 8, 2006. This work was supported in part by the Petroleum Research Fund (PRF-42734-G4) and grants from the National Science Foundation to D.Z. (CHE-0517334) and A.Z. O.O. is grateful for a NASA Harriett Jenkins predoctoral fellowship. D.Z. thanks Professor Sherwin Singer for helpful discussions and Ya-Ting Kao for the initial help.

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