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Published online before print December 20, 2007, 10.1110/ps.073147608
Protein Science (2008), 17:352-361. Published by Cold Spring Harbor Laboratory Press. Copyright © 2008 The Protein Society
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An unusual red-edge excitation and time-dependent Stokes shift in the single tryptophan mutant protein DD-carboxypeptidase from Streptomyces: The role of dynamics and tryptophan rotamers

Giovanni Maglia1,4, Abel Jonckheer1,2, Marc De Maeyer2, Jean-Marie Frère3, and Yves Engelborghs1

1 Laboratory of Biomolecular Dynamics, Department of Chemistry, University of Leuven, Celestijnenlaan 200 G, B-3001 Leuven, Belgium
2 Laboratory of Biomolecular Modeling and BioMacS, Department of Chemistry, University of Leuven, Celestijnenlaan 200 G, B-3001 Leuven, Belgium
3 CIP/Enzymology, Institute of Chemistry B6, Université de Liège, Sart-Tilman, B-4000 Liège, Belgium

(RECEIVED August 1, 2007; FINAL REVISION October 18, 2007; ACCEPTED October 31, 2007)

The fluorescence emission of the single tryptophan (W233) of the mutant protein DD-carboxypeptidase from streptomyces is characterized by a red-edge excitation shift (REES), i.e., the phenomenon that the wavelength of maximum emission depends on the excitation wavelength. This phenomenon is an indication for a strongly reduced dynamic environment of the single tryptophan, which has a very low accessibility to the solvent. The REES shows, however, an unusual temperature and time dependence. This, together with the fluorescence lifetime analysis, showing three resolvable lifetimes, can be explained by the presence of three rotameric states that can be identified using the Dead-End Elimination method. The three individual lifetimes increase with increasing emission wavelength, indicating the presence of restricted protein dynamics within the rotameric states. This is confirmed by time-resolved anisotropy measurements that show dynamics within the rotamers but not among the rotamers. The global picture is that of a protein with a single buried tryptophan showing strongly restricted dynamics within three distinct rotameric states with different emission spectra and an anisotropic environment.

Keywords: tryptophan; fluorescence; lifetime; red-edge excitation shift; DD peptidase


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