Two-dimensional infrared population transfer spectroscopy for enhancing structural markers of proteins

¹ Zernike Institute of Advanced Materials, University of Groningen

^* To whom correspondence should be addressed. E-mail: j.knoester{at}rug.nl.

Submitted on August 17, 2007
Revised on September 4, 2007
Accepted on 20 September 2007

	Abstract

We propose the possibility of using vibrational population transfer to enhance the structural markers for protein motifs that occur in two-dimensional infrared spectroscopy. We demonstrate the potential of this method by calculating the spectrum of the trpzip2 -hairpin peptide, a system that is small enough to allow accurate simulation of its two-dimensional infrared spectra, including vibrational population transfer induced by a fluctuating solvent. The results show that under selected experimental conditions, in particular by using perpendicular polarization and finite waiting times, the cross peaks that constitute the well-known "Z"-shape marker for -sheet structure in two-dimensional spectra are strongly enhanced. This enhancement is shown to result from vibrational population transfer. It should be possible to use the same technique for enhancing cross peaks in other structures and generally improve structural determination by two-dimensional infrared spectroscopy. The simulated population transfer times are in good agreement with those observed in experiments on typical proteins.

Key Words: Tryptophan zipper, Two-dimensional infrared spectroscopy, beta-sheet structure, proteins, structural markers, vibrational population transfer