Biology subjects

Chen, S.-N.

Publications and source records attributed to Chen, S.-N..

3 recordsLinked to original sources

bioRxiv2025

Structural basis of K11/K48-branched ubiquitin chain recognition by the human 26S proteasome

Beyond the canonical K48-linked homotypic polyubiquitination for proteasome-targeted proteolysis, K11/K48-branched ubiquitin (Ub) chains are involved in fast-tracking protein turnover during cell cycle progression and proteotoxic stress. Here, we report cryo-EM structures of human 26S proteasome in a complex with a K11/K48-branched Ub chain. The structures revealed a multivalent substrate recognition mechanism involving a hitherto unknown K11-linked Ub binding site at the groove formed by RPN2 and RPN10 in addition to the canonical K48-linkage binding site formed by RPN10 and RPT4/5 coiled-coil. Additionally, RPN2 recognizes an alternating K11-K48 linkage through a conserved motif similar to the K48-specific T1 binding site of RPN1. The insights gleaned from these structures explain the molecular mechanism underlying the recognition of the K11/K48 branched Ub as a priority signal in the ubiquitin-mediated proteasomal degradation.

biochemistry↗

bioRxiv2022

Inhibition of Aromatase by Hops, Licorice Species, and their bioactive compounds in Postmenopausal Breast Tissue

Breast cancer risk continues to rise post menopause. Endocrine therapies are employed to prevent postmenopausal breast cancer in high-risk women. However, their adverse effects have reduced acceptability and overall success in cancer preventionatural products such as hops (Humulus lupulus) and pharmacopoeial licorice (Glycyrrhiza) species, which are used for managing menopausal symptoms, have demonstrated estrogenic and chemopreventive properties. Their beneficial effects on aromatase activity and expression as important factors in postmenopausal breast carcinogenesis are understudied. The presented data show that Gycyrrhiza inflata (GI) has the highest aromatase inhibition potency among these plants. Moreover, phytoestrogens such as 8-prenylnaringenin from hops as well as liquiritigenin and 8-prenylapigenin from licorice are shown to be potent bioactives, in line with computational docking studies. 8-Prenylnaringenin, GI extract, liquiritigenin, and licochalcone A all suppress aromatase expression in postmenopausal womens breast tissue. Collectively, these data suggest that these natural products may have breast cancer prevention potential for high-risk postmenopausal women.

pharmacology and toxicology↗

bioRxiv2020

In-cell destabilization of a homo-dimeric protein complex detected by DEER spectroscopy

The complexity of the cellular medium can affect proteins properties and therefore in-cell characterization of proteins is essential. We explored the stability and conformation of BIR1, the first baculoviral IAP repeat domain of X-chromosome-linked inhibitor of apoptosis (XIAP), as a model for a homo-dimer protein in human HeLa cells. We employed double electron-electron resonance (DEER) spectroscopy and labeling with redox stable and rigid Gd3+ spin labels at three protein residues, C12 (flexible region), E22C and N28C (part of helical residues 26-31) in the N-terminal region. In contrast to predictions by excluded volume crowding theory, the dimer-monomer dissociation constant KD was markedly higher in cells than in solution and dilute cell lysate. As expected, this increase was recapitulated under conditions of high salt concentrations given that a conserved salt bridge at the dimer interface is critically required for association. Unexpectedly, however, also the addition of a crowding agent such as Ficoll destabilized the dimer, suggesting that Ficoll forms specific interactions with the monomeric protein. Changes in DEER distance distributions were observed for the E22C site, which displayed reduced conformational freedom in cells. Although overall DEER behaviors at E22C and N28C were compatible with a predicted compaction of disordered protein regions by excluded volume effects, we were unable to reproduce E22C properties in artificially crowded solutions. These results highlight the importance of in-cell DEER measurements to appreciate the complexities of cellular in vivo effects on protein structures and functions.

biophysics↗