TY - JOUR
T1 - Vibrational lifetime of the scn protein label in h2o and d2o reports site-specific solvation and structure changes during pyp's photocycle
AU - Schmidt-Engler, Julian M.
AU - Blankenburg, Larissa
AU - Błasiak, Bartosz
AU - Van Wilderen, Luuk J.G.W.
AU - Cho, Minhaeng
AU - Bredenbeck, Jens
N1 - Funding Information:
We thank Sabrina Oesteritz and Hans-Werner Müller for their expertise and help during protein production. Our gratitude is also extended to Ernst Winter for exceptional technical support, Florian Habenstein for the mutation and characterization of A30C* and V57C*, and Georg Wille for discussion. We also thank the Deutsche Forschungsgemeinschaft for funding through INST 161/722-1 FUGG. M.C. thanks the Institute for Basic Science in Korea for funding through IBS-R023-D1.
Publisher Copyright:
© 2019 American Chemical Society.
PY - 2020/1/7
Y1 - 2020/1/7
N2 - The application of vibrational labels such as thiocyanate »(-S-CN) for studying protein structure and dynamics is thriving. Absorption spectroscopy is usually employed to obtain wavenumber and line shape of the label. An observable of great significance might be the vibrational lifetime, which can be obtained by pump probe or 2D-IR spectroscopy. Due to the insulating effect of the heavy sulfur atom in the case of the SCN label, the lifetime of the CN oscillator is expected to be particularly sensitive to its surrounding as it is not dominated by through-bond relaxation. We therefore investigate the vibrational lifetime of the SCN label at various positions in the blue light sensor protein Photoactive Yellow Protein (PYP) in the ground state and signaling state of the photoreceptor. We find that the vibrational lifetime of the CN stretching mode is strongly affected both by its protein environment and by the degree of exposure to the solvent. Even for label positions where the line shape and wavenumber observed by FTIR are barely changing upon activation of the photoreceptor, we find that the lifetime can change considerably. To obtain an unambiguous measure for the solvent exposure of the labeled site, we show that it is imperative to compare the lifetimes in H2O and D2O. Importantly, the lifetimes shorten in H2O as compared to D2O for water exposed labels, while they stay largely the same for buried labels. We quantify this effect by defining a solvent exclusion coefficient (SEC). The response of the label's vibrational lifetime to its solvent exposure renders it a suitable universal probe for protein investigations. This applies even to systems that are otherwise hard to address, such as transient or short-lived states, which could be created during a protein's working cycle (as here in PYP) or during protein folding. It is also applicable to flexible systems (intrinsically disordered proteins), protein-protein and protein-membrane interactions.
AB - The application of vibrational labels such as thiocyanate »(-S-CN) for studying protein structure and dynamics is thriving. Absorption spectroscopy is usually employed to obtain wavenumber and line shape of the label. An observable of great significance might be the vibrational lifetime, which can be obtained by pump probe or 2D-IR spectroscopy. Due to the insulating effect of the heavy sulfur atom in the case of the SCN label, the lifetime of the CN oscillator is expected to be particularly sensitive to its surrounding as it is not dominated by through-bond relaxation. We therefore investigate the vibrational lifetime of the SCN label at various positions in the blue light sensor protein Photoactive Yellow Protein (PYP) in the ground state and signaling state of the photoreceptor. We find that the vibrational lifetime of the CN stretching mode is strongly affected both by its protein environment and by the degree of exposure to the solvent. Even for label positions where the line shape and wavenumber observed by FTIR are barely changing upon activation of the photoreceptor, we find that the lifetime can change considerably. To obtain an unambiguous measure for the solvent exposure of the labeled site, we show that it is imperative to compare the lifetimes in H2O and D2O. Importantly, the lifetimes shorten in H2O as compared to D2O for water exposed labels, while they stay largely the same for buried labels. We quantify this effect by defining a solvent exclusion coefficient (SEC). The response of the label's vibrational lifetime to its solvent exposure renders it a suitable universal probe for protein investigations. This applies even to systems that are otherwise hard to address, such as transient or short-lived states, which could be created during a protein's working cycle (as here in PYP) or during protein folding. It is also applicable to flexible systems (intrinsically disordered proteins), protein-protein and protein-membrane interactions.
UR - http://www.scopus.com/inward/record.url?scp=85076751932&partnerID=8YFLogxK
U2 - 10.1021/acs.analchem.9b03997
DO - 10.1021/acs.analchem.9b03997
M3 - Article
C2 - 31769286
AN - SCOPUS:85076751932
SN - 0003-2700
VL - 92
SP - 1024
EP - 1032
JO - Analytical Chemistry
JF - Analytical Chemistry
IS - 1
ER -