Received October 29, 2006

Abstract:

Two-dimensional infrared spectroscopy in conjunction with hydrogen-deuterium exchange experiments provides detailed information about solvent penetration into protein structure. Correlating the secondary-structure sensitivity of the amide I vibration and the solvent-exposure sensitivity of amide II provides a direct probe of solvent-inaccessible residues of proteins embedded in the hydrophobic core or those involved in strong hydrogen bonds in secondary structures. Distinct spectral signatures of the cross-peak region arising from the coupling of the amide I and II modes imply a significant degree of structural stability of hydrogen-bonded contacts in -helices and -sheets in a series of proteins. Ubiquitin, an /-protein, exhibits strong -helical signatures and lacks those of the -sheet in the cross-peak region, demonstrating that ubiquitin's -sheet exchanges protons with the surrounding solvent and is conformationally unstable.

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