Tryptophan oxidation-induced dynamics highlight why stable γS-crystallin variants aggregate
- 1Department of Chemistry, University of California, Irvine, Irvine, CA 92697-2025, USA
- 2Department of Molecular Biology and Biochemistry, University of California, Irvine, Irvine, CA 92697-3900, USA
- 3School of Population & Public Health, University of California, Irvine, Irvine, CA 92697, USA
Abstract
Human γS-crystallin (γS) is a highly soluble protein found in the eye lens, where it is densely packed with other proteins to form the refractive tissue required for vision. Mutations in γS can compromise its solubility and cause congenital cataract, while post-translational modifications (PTMs) can lead to age-related cataract. γS is especially susceptible to oxidative PTMs, which accumulate from lifelong exposure to UV light. We previously investigated the effects of side-chain oxidation at tryptophan 163 (W163) by incorporating an oxidation mimic, 5-hydroxytryptophan (5HTP), in a site-specific manner using genetic code expansion. The resulting variant, γS-W163(5HTP), retains the overall fold of the wild-type γS (γS-WT) even under thermal and chemical stress, yet readily forms large oligomers at physiological temperature. Here, we probe the mechanism underlying this behavior. We first characterize γS-W163S, a serine variant in which the indole ring at position 163 is effectively removed, to further define the role of W163 in γS-crystallin structure and stability. We also map changes in backbone dynamics caused by W163 oxidation in γS-W163(5HTP) using solution-state NMR. Together, our findings support the established model in which crystallin aggregation is decoupled from global destabilization: although the oxidative modification at W163 is structurally tolerated through rearrangement of the local hydrogen bond network, the resulting changes in backbone flexibility render aggregation-competent conformations accessible. This work provides mechanistic insights into how covalent damage to crystallin monomers promotes aberrant intermolecular interactions that lead to cataract formation.
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BibTeX
@article{seo2026tryptophan,
title = {{Tryptophan oxidation-induced dynamics highlight why stable γS-crystallin variants aggregate}},
author = {Yeonseong Seo and Amanda Abiad and Micco Iwase and Tsoler K. Demerdjian and Linyuting Xing and Minseo Kim and Elizabeth M. Wingen and Rachel W. Martin},
journal = {Biophysical reports},
year = {2026},
month = oct,
doi = {10.1016/j.bpr.2026.100291},
url = {https://europepmc.org/article/PMC/PMC13722077},
note = {CC BY},
}
RIS
TY - JOUR
TI - Tryptophan oxidation-induced dynamics highlight why stable γS-crystallin variants aggregate
AU - Yeonseong Seo
AU - Amanda Abiad
AU - Micco Iwase
AU - Tsoler K. Demerdjian
AU - Linyuting Xing
AU - Minseo Kim
AU - Elizabeth M. Wingen
AU - Rachel W. Martin
PY - 2026
DA - 2026/10/12
JO - Biophysical reports
DO - 10.1016/j.bpr.2026.100291
UR - https://europepmc.org/article/PMC/PMC13722077
AB - Human γS-crystallin (γS) is a highly soluble protein found in the eye lens, where it is densely packed with other proteins to form the refractive tissue required for vision. Mutations in γS can compromise its solubility and cause congenital cataract, while post-translational modifications (PTMs) can lead to age-related cataract. γS is especially susceptible to oxidative PTMs, which accumulate from lifelong exposure to UV light. We previously investigated the effects of side-chain oxidation at tryptophan 163 (W163) by incorporating an oxidation mimic, 5-hydroxytryptophan (5HTP), in a site-specific manner using genetic code expansion. The resulting variant, γS-W163(5HTP), retains the overall fold of the wild-type γS (γS-WT) even under thermal and chemical stress, yet readily forms large oligomers at physiological temperature. Here, we probe the mechanism underlying this behavior. We first characterize γS-W163S, a serine variant in which the indole ring at position 163 is effectively removed, to further define the role of W163 in γS-crystallin structure and stability. We also map changes in backbone dynamics caused by W163 oxidation in γS-W163(5HTP) using solution-state NMR. Together, our findings support the established model in which crystallin aggregation is decoupled from global destabilization: although the oxidative modification at W163 is structurally tolerated through rearrangement of the local hydrogen bond network, the resulting changes in backbone flexibility render aggregation-competent conformations accessible. This work provides mechanistic insights into how covalent damage to crystallin monomers promotes aberrant intermolecular interactions that lead to cataract formation.
SN - 2667-0747
ER -