In situ structural biology of human immune defence

Structural biology provides insights into protein function but generally requires purified complexes, which necessitates removing the protein from its native context. We therefore lose in situ information. Cryo-electron tomography (cryoET) provides this information, but finding a specific protein in a cell is akin to searching for a needle in a haystack 50 m tall. We are at the forefront of developing a technique to solve this problem; by combining super-resolution (SR) light microscopy on samples prepared for cryoET we can locate specific proteins and events within whole mammalian cells. This information can be correlated with 3D cryoET volumes to perform in situ structural biology. We call this technique super-resolution cryo-correlative light and electron microscopy (SRcryoCLEM). Here, I describe how we will enhance SRcryoCLEM and use it to image antibody-activated aspects of human immunity, enabling the development of cutting-edge immunotherapeutics. The first aim of this proposal is to augment SRcryoCLEM with multicolour imaging and automated data analysis. Spectrally-distinct fluorescent proteins will be identified that are ideal for cryoSR imaging, and AI-based volume segmentation and automated particle picking will help to democratise in situ structural biology. The second aim is to deliver in situ structural data to explain discrepancies in antibody effector functions with an unknown structural cause, which will be used to perform structure guided antibody design to further enhance their effector functions for the benefit of human health.The third aim is to discover the structural determinants orchestrating antibody-mediated phagocytosis by macrophages using SRcryoCLEM. This immunologically-pivotal mechanism is poorly understood, but is being exploited as a next-generation therapeutic. Our data will provide crucial insights into the fundamental biological processes underlying macrophage function, allowing therapeutic gain.