Board 14: Investigating the Potential of the M3-M4 Loop of the Glycine Receptor to Act as a Cell Penetrating Peptide

Student Scientist: Audrey Calvin ’23
Research Mentor: Kayce Tomcho (OWU Department of Chemistry)

A multitude of cars exist on the market which vary in capability. To the average buyer, an engine looks similar between car brands, but a mechanic understands that the intricacies of the engine are related to its performance. The proteins of our body work similarly. When structures vary between proteins, their differences ultimately lead to a distinct function. Our research examines the structure of the intracellular M3-M4 loop of one type of protein, the Glycine Receptor (GlyR). By understanding the function of GlyR, we can build more specific tools to treat diseases linked to this protein; in the same way a specific car would require a specific tool to fix it.

Our cells contain a vast number of proteins that perform countless functions. For every different function, a specific structure coincides. To date, many techniques are used to reveal protein structures including x-ray diffraction and cryo-electron microscopy. These approaches have disadvantages as they are often expensive and require samples of high purity and stability. One method, cross-linking mass spectrometry (CX-MS) has proved advantageous. With CX-MS, a cross-linker is covalently bonded to a known mutation in a protein, and another inter or intra-cellular bond is formed nearby. These distance constraints are analyzed using mass spectrometry which can help elucidate existing structural models. The structure and dynamics of the glycine receptor (GlyR) has been extensively studied using multiple techniques, however; the structure of the intracellular M3-M4 loop remains unclear. Previous CX-MS studies (Tomcho et al.) have shown distance measurements that suggest the loop is very dynamic and may be able to penetrate the membrane and interact with the extracellular domain. Our study has designed a workflow to better understand this mechanism. We hypothesize that the loop is traversing the membrane in a similar fashion as a cell-penetrating peptide (CPP). CPPs are short peptides that cross over the cell’s membrane and often contain basic residues such as arginine and lysine. Our experimental design attempts to interact portions of the loop with the cell membrane using co-sedimentation techniques for analysis. Further defining the structure of GlyR may lead to developing targeted therapeutics for its associated diseases.