VitisC: Visualizing interested target via integrated scaffold of cytoophidium

Cryo-electron microscopy (cryo-EM) single-particle analysis has become a widely used technique for high-resolution structural determination of biological macromolecules and complexes. However, the determination of the structure of small molecule proteins remains a limitation of this technology. To address this issue, here we develop a novel approach termed Visualizing interested target via integrated scaffold of cytoophidium (VitisC). We use a filamentous structure formed by Escherichia coli CTP synthase (CTPS) as the scaffold, termed the scaffold of cytoophidium. Through artificial design and modification, small proteins can be attached to this symmetrical scaffold, which is very suitable for cryo-EM imaging. The formation conditions for stable filament structures of the fusion protein are optimized in vitro, and the three-dimensional structure of the fusion protein is reconstructed using cryo-EM single-particle analysis, achieving an overall resolution of 3.39 Å. Therefore, cryo-EM is successfully applied to visualize small proteins. VitisC not only demonstrates the feasibility of employing cytoophidia as scaffolds, but also provides an approach for high-resolution structural analysis of small proteins using Cryo-EM.