The Structure of the Mouse Serotonin 5-HT3 Receptor in Lipid Vesicles

• 5-HT3 receptors are imaged in lipid bilayers by cryo electron tomography
• Subtomogram averaging resulted in a 3D structure at 12 Å resolution
• No major differences were found between EM and X-ray structures
• Inter-receptor interactions in the membrane are mediated by short horizontal helices

SummaryThe function of membrane proteins is best understood if their structure in the lipid membrane is known. Here, we determined the structure of the mouse serotonin 5-HT3 receptor inserted in lipid bilayers to a resolution of 12 Å without stabilizing antibodies by cryo electron tomography and subtomogram averaging. The reconstruction reveals protein secondary structure elements in the transmembrane region, the extracellular pore, and the transmembrane channel pathway, showing an overall similarity to the available X-ray model of the truncated 5-HT3 receptor determined in the presence of a stabilizing nanobody. Structural analysis of the 5-HT3 receptor embedded in a lipid bilayer allowed the position of the membrane to be determined. Interactions between the densely packed receptors in lipids were visualized, revealing that the interactions were maintained by the short horizontal helices. In combination with methodological improvements, our approach enables the structural analysis of membrane proteins in response to voltage and ligand gating.

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