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Electrostatic stabilization of a native protein structure in the gas phase.

Breuker K, Brüschweiler S, Tollinger M - Angew. Chem. Int. Ed. Engl. (2010)

View Article: PubMed Central - PubMed

Affiliation: Institut für Organische Chemie and Center for Molecular Biosciences Innsbruck, Universität Innsbruck, Innrain 52a, 6020 Innsbruck, Austria. kathrin.breuker@uibk.ac.at

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Recently, a general picture has been proposed of how long, and to what extent, native protein structure can be retained in the gas phase... In particular, molecular dynamics simulations suggest that salt bridges and ionic hydrogen bonds on the protein surface can transiently stabilize the global fold shortly after desolvation... We demonstrate that in the gas phase, the most stable regions are those stabilized by salt bridges and ionic hydrogen bonds... The data in Figure 2 provide substantial evidence for a correlation between the solution- and gas-phase structures of KIX... This supposition is corroborated by ECD of 12+ ions generated by nano-ESI from a solution (in H2O at pH 4.5) that better resembles the native protein environment, which gave decreased - and -ion yields in the α2 and α3 regions (see Figure S4 in the Supporting Information), along with a smaller total fragment ion yield (37 %) relative to that resulting from ECD of 12+ ions from ESI of solutions in H2O/CH3OH (80:20) at pH 4 (total fragment-ion yield: 49 %; see Figure S3 in the Supporting Information)... This behavior is also reflected in the site-specific transition charge values from analysis of site-specific - and -ion yields (see Figure S6 in the Supporting Information), which generally increase from the N to the C terminus (Figure 4b)... Transition charge values for cleavage sites between helix regions (31–41, 62–64) are similar to values for adjacent helix ends, indicating that helix separation does not precede helix unraveling... This observation strongly suggests that interactions involving charged residues, that is, ionic hydrogen bonds and salt bridges, largely determine helix stability in the gas phase... The density of salt bridges correlates (r=0.9999) with transition charge values (Figure 6b) even better than the density of charged residues, suggesting that salt bridges are major determinants for protein structural stabilization in the gas phase... However, this conclusion does not exclude additional stabilization by ionic hydrogen bonds as well as charge–dipole interactions... We show here that electrostatic interactions can compensate for the loss of hydrophobic bonding and stabilize the native three-helix bundle structure of KIX in the gas phase on a timescale of at least 4 s... Among these interactions, salt bridges were found to play a dominant role... However, a high number of surface-exposed charged residues alone does not guarantee protein stability in the gas phase: equine Cytochrome c has 24 basic and 12 acidic residues, with the number of salt bridges on the protein surface increasing from 6 in solution to an average value of 17.3 in the gas phase within 10 ps after desolvation, yet its native fold disintegrates on a timescale of milliseconds., The outstanding stability of gaseous KIX ions observed in this study must be attributed to the combination of favorable electrostatic interactions, including salt bridges, neutral and ionic hydrogen bonds, as well as charge–dipole interactions.

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Analysis of the data in Figure 2: a) integrated c- and z•-ion yields for helix regions α1, α2, and α3 versus precursor ion charge; b) site-specific transition charge values (at 50 % of plateau value) versus backbone cleavage site; symbol size and error bars represent plateau values and standard deviations for transition charge values from sigmoidal fit functions, respectively.
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fig04: Analysis of the data in Figure 2: a) integrated c- and z•-ion yields for helix regions α1, α2, and α3 versus precursor ion charge; b) site-specific transition charge values (at 50 % of plateau value) versus backbone cleavage site; symbol size and error bars represent plateau values and standard deviations for transition charge values from sigmoidal fit functions, respectively.

Mentions: Figure 4a shows integrated c- and z•-ion yields for helix regions α1, α2, and α3 versus precursor ion charge. The data exhibit sigmoidal behavior, with transition charge values (at 50 % of the plateau value) of 9.2, 10.7, and 12.4 for α1, α2, and α3, respectively. This order of helix stability (α3>α2>α1) in the gas phase agrees with that in solution as determined by NMR spectroscopic experiments.10 However, in solution, each helix unfolds cooperatively,10 whereas the gas-phase data (Figure 1) show incremental unraveling from their N-terminal ends. This behavior is also reflected in the site-specific transition charge values from analysis of site-specific c- and z•-ion yields (see Figure S6 in the Supporting Information), which generally increase from the N to the C terminus (Figure 4b). Transition charge values for cleavage sites between helix regions (31–41, 62–64) are similar to values for adjacent helix ends, indicating that helix separation does not precede helix unraveling.


Electrostatic stabilization of a native protein structure in the gas phase.

Breuker K, Brüschweiler S, Tollinger M - Angew. Chem. Int. Ed. Engl. (2010)

Analysis of the data in Figure 2: a) integrated c- and z•-ion yields for helix regions α1, α2, and α3 versus precursor ion charge; b) site-specific transition charge values (at 50 % of plateau value) versus backbone cleavage site; symbol size and error bars represent plateau values and standard deviations for transition charge values from sigmoidal fit functions, respectively.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3045662&req=5

fig04: Analysis of the data in Figure 2: a) integrated c- and z•-ion yields for helix regions α1, α2, and α3 versus precursor ion charge; b) site-specific transition charge values (at 50 % of plateau value) versus backbone cleavage site; symbol size and error bars represent plateau values and standard deviations for transition charge values from sigmoidal fit functions, respectively.
Mentions: Figure 4a shows integrated c- and z•-ion yields for helix regions α1, α2, and α3 versus precursor ion charge. The data exhibit sigmoidal behavior, with transition charge values (at 50 % of the plateau value) of 9.2, 10.7, and 12.4 for α1, α2, and α3, respectively. This order of helix stability (α3>α2>α1) in the gas phase agrees with that in solution as determined by NMR spectroscopic experiments.10 However, in solution, each helix unfolds cooperatively,10 whereas the gas-phase data (Figure 1) show incremental unraveling from their N-terminal ends. This behavior is also reflected in the site-specific transition charge values from analysis of site-specific c- and z•-ion yields (see Figure S6 in the Supporting Information), which generally increase from the N to the C terminus (Figure 4b). Transition charge values for cleavage sites between helix regions (31–41, 62–64) are similar to values for adjacent helix ends, indicating that helix separation does not precede helix unraveling.

View Article: PubMed Central - PubMed

Affiliation: Institut für Organische Chemie and Center for Molecular Biosciences Innsbruck, Universität Innsbruck, Innrain 52a, 6020 Innsbruck, Austria. kathrin.breuker@uibk.ac.at

AUTOMATICALLY GENERATED EXCERPT
Please rate it.

Recently, a general picture has been proposed of how long, and to what extent, native protein structure can be retained in the gas phase... In particular, molecular dynamics simulations suggest that salt bridges and ionic hydrogen bonds on the protein surface can transiently stabilize the global fold shortly after desolvation... We demonstrate that in the gas phase, the most stable regions are those stabilized by salt bridges and ionic hydrogen bonds... The data in Figure 2 provide substantial evidence for a correlation between the solution- and gas-phase structures of KIX... This supposition is corroborated by ECD of 12+ ions generated by nano-ESI from a solution (in H2O at pH 4.5) that better resembles the native protein environment, which gave decreased - and -ion yields in the α2 and α3 regions (see Figure S4 in the Supporting Information), along with a smaller total fragment ion yield (37 %) relative to that resulting from ECD of 12+ ions from ESI of solutions in H2O/CH3OH (80:20) at pH 4 (total fragment-ion yield: 49 %; see Figure S3 in the Supporting Information)... This behavior is also reflected in the site-specific transition charge values from analysis of site-specific - and -ion yields (see Figure S6 in the Supporting Information), which generally increase from the N to the C terminus (Figure 4b)... Transition charge values for cleavage sites between helix regions (31–41, 62–64) are similar to values for adjacent helix ends, indicating that helix separation does not precede helix unraveling... This observation strongly suggests that interactions involving charged residues, that is, ionic hydrogen bonds and salt bridges, largely determine helix stability in the gas phase... The density of salt bridges correlates (r=0.9999) with transition charge values (Figure 6b) even better than the density of charged residues, suggesting that salt bridges are major determinants for protein structural stabilization in the gas phase... However, this conclusion does not exclude additional stabilization by ionic hydrogen bonds as well as charge–dipole interactions... We show here that electrostatic interactions can compensate for the loss of hydrophobic bonding and stabilize the native three-helix bundle structure of KIX in the gas phase on a timescale of at least 4 s... Among these interactions, salt bridges were found to play a dominant role... However, a high number of surface-exposed charged residues alone does not guarantee protein stability in the gas phase: equine Cytochrome c has 24 basic and 12 acidic residues, with the number of salt bridges on the protein surface increasing from 6 in solution to an average value of 17.3 in the gas phase within 10 ps after desolvation, yet its native fold disintegrates on a timescale of milliseconds., The outstanding stability of gaseous KIX ions observed in this study must be attributed to the combination of favorable electrostatic interactions, including salt bridges, neutral and ionic hydrogen bonds, as well as charge–dipole interactions.

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