Ruilin Qian

Advisor: Prof. Shu-ou Shan · I investigated the mechanism of co-translational protein targeting pathway mediated by the Signal Recognition Particle (SRP) and SRP receptor (SR), which deliver ribosome–nascent chain complexes (RNCs) to the Sec61 translocon on the endoplasmic reticulum (ER) membrane. · I performed in vitro transcription/translation of truncated mRNAs to stall ribosomes and capture RNCs. And I expressed and purified SRP, SRP receptor, and other proteins engaged in this process from E.coli, yeast, insect, and mammalian cells. Guided by their structures, I designed mutants to investigate the mechanisms of protein function. · I developed biochemical and biological assays, including but not limited to fluorescence, Western Blot, and chemical crosslinking, to dissect SRP–RNC–SR–translocon interactions and uncover modulatory factors. For fluorescence assay, I established site-specific bioconjugation methods to label proteins with fluorophores via click chemistry and enzymatic reactions. · I am building mechanistic models of this co-translational protein targeting process. From this project, I gained extensive expertise in macromolecule (protein and RNA) production, purification, and interaction measurement.

· I developed a high-throughput platform to quantify monoclonal antibodies’ (mAbs) reduction propensity by the thioredoxin/thioredoxin reductase (Trx/TrxR) system in vitro, providing insights into the relationship between mAb structure and reduction, and enabling the design of more stable mAbs. Using this platform, I also identified two novel inhibitors of the Trx/TrxR system that protect mAbs from reduction during production. · I collaborated with the bioanalytical team to monitor the dissociation of heavy and light chains after reduction, using UP-SEC and CE-SDS methods. · I established a rapid workflow to quantify Trx and TrxR levels in harvested cell culture fluid (HCCF) by ELISA and enzymatic assay, supporting optimization of cell lines and culture conditions. Leveraging this workflow, I evaluated the clearance efficiency of different resins on these two enzymes and investigated the underlying clearance mechanisms.

Advisor: Prof. Yangzhong Liu · I conducted high-throughput screening from herbal extracts to identify natural inhibitors against the E3 ligase MDM2, whose overexpression downregulates p53 tumor suppressor protein, thereby contributing to the development of various types of cancer. · I purified the active components using analytical chemistry techniques such as liquid-liquid extraction, TLC, and HPLC, and quantified their inhibitory effects in vitro using methods like ITC.