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Charge-Transfer Transitions in the Vacuum-Ultraviolet of Protein Circular Dichroism Spectra
journal contribution
posted on 2008-02-14, 00:00 authored by Benjamin M. Bulheller, Andrew J. Miles, B. A. Wallace, Jonathan D. HirstCircular dichroism (CD) is widely used in the structural characterization and secondary structure determination
of proteins. The vacuum UV region (below 190 nm), where charge-transfer transitions have an influence on
the CD spectra, can be accessed using synchrotron radiation circular dichroism (SRCD) spectroscopy. Recently,
charge-transfer transitions in a conformationally diverse set of dipeptides have been characterized ab initio
using complete active space self-consistent field calculations, and the relevant charge distributions have been
parametrized for use in the matrix method for calculations of protein CD. Here, we present calculations of
the vacuum UV CD spectra of 71 proteins, for which experimental SRCD spectra and X-ray crystal structures
are available. The theoretical spectra are calculated considering charge-transfer and side chain transitions.
This significantly improves the agreement with experiment, raising the Spearman correlation coefficient between
the calculated and the experimental intensity at 175 nm from 0.12 to 0.79. The influence of the conformation
on charge-transfer transitions is analyzed in detail, showing that the n → π* charge-transfer transitions are
most important in α-helical proteins, whereas in β strand proteins the π → π* charge-transfer transition
along the chain in the amino- to carboxy-end direction is most dominant.
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field calculationsmatrix methodCD spectraProtein Circular Dichroism SpectraCircular dichroism175 nmSpearman correlation coefficientvacuum UV CD spectraβ strand proteins71 proteinsSRCD spectrasynchrotron radiationcharge distributionsvacuum UV regionprotein CDab initiostructure determinationside chain transitions
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