Southwest Jiaotong University 2 articles published in JoVE Chemistry Construction of Cyclic Cell-Penetrating Peptides for Enhanced Penetration of Biological Barriers Dan Fang1, Rui Wang1, Xinyi Yu1, Yuan Tian1 1Sichuan Engineering Research Center for Biomimetic Synthesis of Natural Drugs, School of Life Science and Engineering, Southwest Jiaotong University This protocol describes the synthesis of cyclic cell-penetrating peptides with aromatic cross-links and the evaluation of their permeability across biological barriers. Immunology and Infection Screening Peptides that Activate MRGPRX2 using Engineered HEK Cells Shammy Raj1, Lei Lu2, Larry D. Unsworth1 1Department of Chemical and Materials Engineering, Donadeo Innovation Centre for Engineering, University of Alberta, 2School of Life Science and Engineering, Southwest Jiaotong University Techniques for generating a library of short peptides that can activate mast cells via the MRGPRX2 receptor are described. Associated techniques are easy, inexpensive, and can be extended to other cell receptors.