| Autor: |
Deniz E; Institute of Biophysics, Goethe University Frankfurt am Main, Frankfurt am Main 60438, Germany., Schmidt-Engler JM; Institute of Biophysics, Goethe University Frankfurt am Main, Frankfurt am Main 60438, Germany., Ulrich K; Institute of Biophysics, Goethe University Frankfurt am Main, Frankfurt am Main 60438, Germany., Oberle M; Institute of Biophysics, Goethe University Frankfurt am Main, Frankfurt am Main 60438, Germany., Wille G; Institute of Biophysics, Goethe University Frankfurt am Main, Frankfurt am Main 60438, Germany., Bredenbeck J; Institute of Biophysics, Goethe University Frankfurt am Main, Frankfurt am Main 60438, Germany. |
| Abstrakt: |
Cysteine S-H bonds have a spectroscopically convenient stretching frequency of ∼2550 cm -1 . However, their cross section is low, and the band can be strongly broadened in heterogeneous environments, making detection very challenging. With two-dimensional infrared (2D-IR) setups achieving ever higher sensitivities in recent years, systematic use of the weak cysteine sulfhydryls (Cys-SHs) absorption band is now within reach, even at low millimolar protein concentrations. Here, we demonstrate the capabilities of Cys-SH as an intrinsic 2D-IR label in pyruvate oxidase from E. coli, an enzyme with ten cysteines in its native sequence. 1D-IR measurements on the wild-type and individual cysteine knock-out variants show that two such residues have especially narrow SH signatures, caused by their intrahelical hydrogen bonding. 2D-IR analysis of these bands reveals an extraordinarily high anharmonicity (∼110 cm -1 ) and a long vibrational lifetime (∼4 ps). This allows monitoring spectral diffusion via center line slope analysis for up to 10 ps-separately for both the ground and excited states. The unique spectroscopic features and its ease of introduction make Cys-SH a useful IR spectroscopic label. |
