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Hydration of guanidinium depends on its local environment.

ABSTRACT: Hydration of gaseous guanidinium (Gdm⁺) with up to 100 water molecules attached was investigated using infrared photodissociation spectroscopy in the hydrogen stretch region between 2900 and 3800 cm^-1. Comparisons to IR spectra of low-energy computed structures indicate that at small cluster size, water interacts strongly with Gdm⁺ with three inner shell water molecules each accepting two hydrogen bonds from adjacent NH₂ groups in Gdm⁺. Comparisons to results for tetramethylammonium (TMA⁺) and Na⁺ enable structural information for larger clusters to be obtained. The similarity in the bonded OH region for Gdm(H₂O)₂₀⁺vs. Gdm(H₂O)₁₀₀⁺ and the similarity in the bonded OH regions between Gdm⁺ and TMA⁺ but not Na⁺ for clusters with <50 water molecules indicate that Gdm⁺ does not significantly affect the hydrogen-bonding network of water molecules at large size. These results indicate that the hydration around Gdm⁺ changes for clusters with more than about eight water molecules to one in which inner shell water molecules only accept a single H-bond from Gdm⁺. More effective H-bonding drives this change in inner-shell water molecule binding to other water molecules. These results show that hydration of Gdm⁺ depends on its local environment, and that Gdm⁺ will interact with water even more strongly in an environment where water is partially excluded, such as the surface of a protein. This enhanced hydration in a limited solvation environment may provide new insights into the effectiveness of Gdm⁺ as a protein denaturant.

SUBMITTER: Heiles S

PROVIDER: S-EPMC5490459 | biostudies-literature | 2015 Jun

REPOSITORIES: biostudies-literature

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Hydration of guanidinium depends on its local environment.

Heiles Sven S Cooper Richard J RJ DiTucci Matthew J MJ Williams Evan R ER

Chemical science 20150414 6

Hydration of gaseous guanidinium (Gdm+) with up to 100 water molecules attached was investigated using infrared photodissociation spectroscopy in the hydrogen stretch region between 2900 and 3800 cm-1. Comparisons to IR spectra of low-energy computed structures indicate that at small cluster size, water interacts strongly with Gdm+ with three inner shell water molecules each accepting two hydrogen bonds from adjacent NH2 groups in Gdm+. Comp ...[more]

PMID: 28706704

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Project description:Disulfide bonds are covalent bonds that connect nonlocal fragments of proteins, and they are unique post-translational modifications of proteins. They require the oxidizing environment to be stable, which occurs for example during oxidative stress; however, in a cell the reductive environment is maintained, lowering their stability. Despite many years of research on disulfide bonds, their role in the protein life cycle is not fully understood and seems to strictly depend on a system or process in which they are involved. In this article, coarse-grained UNited RESidue (UNRES), and all-atom Assisted Model Building with Energy Refinement (AMBER) force fields were applied to run a series of steered molecular dynamics (SMD) simulations of one of the most studied, but still not fully understood, proteins─ribonuclease A (RNase A). SMD simulations were performed to study the mechanical stability of RNase A in different oxidative-reductive environments. As disulfide bonds (and any other covalent bonds) cannot break/form in any classical all-atom force field, we applied additional restraints between sulfur atoms of reduced cysteines which were able to mimic the breaking of the disulfide bonds. On the other hand, the coarse-grained UNRES force field enables us to study the breaking/formation of the disulfide bonds and control the reducing/oxidizing environment owing to the presence of the designed distance/orientation-dependent potential. This study reveals that disulfide bonds have a strong influence on the mechanical stability of RNase A only in a highly oxidative environment. However, the local stability of the secondary structure seems to play a major factor in the overall stability of the protein. Both our thermal unfolding and mechanical stretching studies show that the most stable disulfide bond is Cys65-Cys72. The breaking of disulfide bonds Cys26-Cys84 and Cys58-Cys110 is associated with large force peaks. They are structural bridges, which are mostly responsible for stabilizing the RNase A conformation, while the presence of the remaining two bonds (Cys65-Cys72 and Cys40-Cys95) is most likely connected with the enzymatic activity rather than the structural stability of RNase A in the cytoplasm. Our results prove that disulfide bonds are indeed stabilizing fragments of the proteins, but their role is strongly redox environment-dependent.

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Hydration of guanidinium depends on its local environment.

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Hydration of guanidinium depends on its local environment.

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