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The enzyme Candida Antarctica lipase B (CALB) serves here as a model for understanding connections among hydration layer dynamics, solvation shell structure, and protein surface structure. The structure and dynamics of water molecules in the hydration layer were characterized for regions of the CALB surface, divided around each α-helix, β-sheet, and loop structure. Heterogeneous hydration dynamics were observed around the surface of the enzyme, in line with spectroscopic observations of other proteins. Regional differences in the structure of the biomolecular hydration layer were found to be concomitant with variations in dynamics. In particular, it was seen that regions of higher density exhibit faster water dynamics. This is analogous to the behavior of bulk water, where dynamics (diffusion coefficients) are connected to water structure (density and tetrahedrality) by excess (or pair) entropy, detailed in the Rosenfeld scaling relationship. Additionally, effects of protein surface topology and hydrophobicity on water structure and dynamics were evaluated using multiregression analysis, showing that topology has a somewhat larger effect on hydration layer structure–dynamics. Concave and hydrophobic protein surfaces favor a less dense and more tetrahedral solvation layer, akin to a more ice-like structure, with slower dynamics. Results show that pairwise entropies of local hydration layers, calculated from regional radial distribution functions, scale logarithmically with local hydration dynamics. Thus, the Rosenfeld relationship describes the heterogeneous structure–dynamics of the hydration layer around the enzyme CALB. These findings raise the question of whether this may be a general principle for understanding the structure–dynamics of biomolecular solvation.
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This content will become publicly available on October 21, 2026
Hydration of tryptophan probed by triplet lifetime isotope effect
Water plays an essential role in the structures, dynamics, and functions of proteins. The experimental determination of the presence of water in proteins remains a challenge. Tryptophan and its derivatives are well-studied molecules whose photophysical properties are sensitive to the local environment. In particular, the lifetime of the triplet state is impacted by the presence of nearby water via coupling to high-frequency vibrational modes of solvent. The ratio of the indole triplet lifetimes in D2O and H2O (τD/τH), called the triplet lifetime isotope effect (3LIE), is 1.6. The feasibility of using measurements of 3LIE to assess hydration of tryptophan residues in proteins was explored, with focus on a membrane-associated model compound, tryptophan octyl-ester; soluble proteins, human serum albumin and ribonuclease T1; the membrane peptide melittin; a leucine-rich synthetic membrane peptide we call leucimer; and the membrane protein outer membrane protein A. The results indicate that while there is variation in the triplet lifetimes depending on the local environment, the value of 3LIE reflects the absence (3LIE = 1.0) or presence (3LIE > 1.0) of nearby water. Molecular dynamics simulations support this interpretation. The mechanism and number of water O–H bonds that couple to the triplet state were explored. These findings suggest that measurements of 3LIE can be applied to directly monitor changes in the hydration of proteins.
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- Award ID(s):
- 2004081
- PAR ID:
- 10646707
- Publisher / Repository:
- AIP
- Date Published:
- Journal Name:
- The Journal of Chemical Physics
- Volume:
- 163
- Issue:
- 15
- ISSN:
- 0021-9606
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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