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Experimentally-Determined Strengths of Atom-Atom (C, N, O) Interactions Responsible for Protein Self-Assembly in Water: Applications to Folding and Other Protein Processes

Xian Cheng, Irina A. Shkel, Kevin O’Connor, M. Thomas Record Jr.
doi: https://doi.org/10.1101/2020.05.26.104851
Xian Cheng
1Program in Biophysics, University of Wisconsin – Madison, Madison WI 53706
2Departments of Biochemistry, University of Wisconsin – Madison, Madison WI 53706
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Irina A. Shkel
2Departments of Biochemistry, University of Wisconsin – Madison, Madison WI 53706
3Departments of Chemistry,University of Wisconsin – Madison, Madison WI 53706
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Kevin O’Connor
2Departments of Biochemistry, University of Wisconsin – Madison, Madison WI 53706
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M. Thomas Record Jr.
1Program in Biophysics, University of Wisconsin – Madison, Madison WI 53706
2Departments of Biochemistry, University of Wisconsin – Madison, Madison WI 53706
3Departments of Chemistry,University of Wisconsin – Madison, Madison WI 53706
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  • For correspondence: mtrecord@wisc.edu
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Abstract

Folding and other protein self-assembly processes are driven by favorable interactions between O, N, and C unified atoms of the polypeptide backbone and sidechains. These processes are perturbed by solutes that interact with these atoms differently than water does. C=O···HN hydrogen bonding and various π-system interactions have been better-characterized structurally or by simulations than experimentally in water, and unfavorable interactions are relatively uncharacterized. To address this situation, we previously quantified interactions of alkylureas with amide and aromatic compounds, relative to interactions with water. Analysis yielded strengths of interaction of each alkylurea with unit areas of different hybridization states of unified O, N, C atoms of amide and aromatic compounds. Here, by osmometry, we quantify interactions of ten pairs of amides selected to complete this dataset. A novel analysis yields intrinsic strengths of six favorable and four unfavorable atom-atom interactions, expressed per unit area of each atom and relative to interactions with water. The most favorable interactions are sp2O - sp2C (lone pair-π, presumably n-π*), sp2C - sp2C (π-π and/or hydrophobic), sp2O-sp2N (hydrogen bonding) and sp3C-sp2C (CH-π and/or hydrophobic). Interactions of sp3C with itself (hydrophobic) and with sp2N are modestly favorable, while sp2N interactions with sp2N and with amide/aromatic sp2C are modestly unfavorable. Amide sp2O-sp2O interactions and sp2O-sp3C interactions are more unfavorable, indicating the preference of amide sp2O to interact with water. These intrinsic interaction strengths are used to predict interactions of amides with proteins and chemical effects of amides (including urea, N-ethylpyrrolidone (NEP), and polyvinyl-pyrrolidone (PVP)) on protein stability.

Significance Quantitative information about strengths of amide nitrogen-amide oxygen hydrogen bonds and π-system and hydrophobic interactions involving amide-context sp2 and/or sp3 carbons is needed to assess their contributions to specificity and stability of protein folds and assemblies in water, as well as to predict or interpret how urea and other amides interact with proteins and affect protein processes. Here we obtain this information from thermodynamic measurements of interactions between small amide molecules in water and a novel analysis that determines intrinsic strengths of atom-atom interactions, relative to water and per unit area of each atom-type present in amide compounds. These findings allow prediction or interpretation of effects of any amide on protein processes from structure, and may be useful to analyze protein interfaces.

Competing Interest Statement

The authors have declared no competing interest.

Copyright 
The copyright holder for this preprint is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is made available under a CC-BY-NC-ND 4.0 International license.
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Posted May 27, 2020.
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Experimentally-Determined Strengths of Atom-Atom (C, N, O) Interactions Responsible for Protein Self-Assembly in Water: Applications to Folding and Other Protein Processes
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Experimentally-Determined Strengths of Atom-Atom (C, N, O) Interactions Responsible for Protein Self-Assembly in Water: Applications to Folding and Other Protein Processes
Xian Cheng, Irina A. Shkel, Kevin O’Connor, M. Thomas Record Jr.
bioRxiv 2020.05.26.104851; doi: https://doi.org/10.1101/2020.05.26.104851
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Experimentally-Determined Strengths of Atom-Atom (C, N, O) Interactions Responsible for Protein Self-Assembly in Water: Applications to Folding and Other Protein Processes
Xian Cheng, Irina A. Shkel, Kevin O’Connor, M. Thomas Record Jr.
bioRxiv 2020.05.26.104851; doi: https://doi.org/10.1101/2020.05.26.104851

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