The function of immune cells like neutrophils, macrophages, and T cells is tightly regulated and controlled by cell surface receptors. Those integral membrane receptors usually possess one or multiple transmembrane helices. They can sense diverse diffusible signaling molecules including hormones, peptides, lipids, and ions or signaling molecules presented on other cells to transmit signals to the intracellular compartment and induce various signaling pathways. We take multiple approaches in structural biology including crystallography and cryo-EM to study the molecular mechanisms underlying signal transduction of immune receptors. We also use methods in structure-based drug design (SBDD) and combinatorial biology such as yeast display to design novel ligands including antibodies to better regulate the activities of immune cells in various disease settings.
Structure and pharmacology of G protein-coupled receptors (GPCRs) in inflamation
GPCRs are a family of cell surface receptors with over 700 members. They can sense diffusible signaling molecules and then undergo complex conformational changes to activate or recruit intracellular effectors including heterotrimeric G proteins and β-arrestins. All GPCRs share a conserved structural topology characterized by 7-transmembrane helices (they are also called 7-TM receptors). GPCRs have been heavily investigated in the pharmaceutical industry, and they constitute 30-40% of current drug targets. A thorough molecular understanding of how endogenous and synthetic ligands act on different GPCRs to regulate their activities is of great importance to drug development for a broad spectrum of diseases.
We have used lipidic cubic phase (LCP) crystallography and cryo-EM to solve structures of multipole GPCRs and GPCR signaling complexes with diverse ligands, which have revealed critical insights into orthosteric and allosteric ligands recognition, receptor activation, G protein-coupling, and biased signaling. Currently, we focus on a group of GPCRs expressed in leukocytes that regulate inflammation. Some of those receptors including the C5a receptor 1 (C5aR) and the prostaglandin D2 receptor 2 (CRTH2, or DP2) can mediate chemotaxis of leukocytes and the release of inflammatory mediators to induce acute inlammatory reponses. Antagonists of these receptors are being developed as novel anti-inflammatory therapeutics. On the other hand, some receptors such as formylpeptide receptors (FPRs), chemerin receptors (ChemR23) and the cannabinoid receptor CB2 can induce anti-inflammatory or 'pro-resolving' signaling pathways to actively resolve inflammation and promote tissues repair. Agonists of these receptors thus represent a novel therapeutic frontier for various inflammatory pathologies including asthma and cardiovascular diseases. Our research goal is to reveal the molecular basis for how those GPCRs regonize diverse pro-inflammatory and pro-resolving agents to induce distinct physiological functions. We also perform structure-based drug design (SBDD) in collaboration with experts in computational biology to ddevelop novel ligands for those receptors.
Development of functional antibodies and engineered proteins targeting immune receptors
Another important project in the lab is to develop functional antibodies and engineer proteins as useful tools and potential therapeutics to regulate activities of immune receptors including GPCRs. One technique we use is yeast display. We screen a naive synthetic library of single-chain antibodies, also known as nanobodies (Nbs), displayed on yeasts to find functional Nbs as GPCR agonists or antagonists. We use novel screening strategies designed based on our structures. We also use molecular evolution methods combined with yeast display to engineer proteins as ligands of immune receptors in order to gain desired pharmacological properties such as high specificity, high affinity or biased agonism.
Structure-based drug design and high throughput screening to develop small-molecule ligands for orphan GPCRs
Through extensive collaborations, we use methods in structure-based drug design (SBDD) and high throughput screening (HTS) to find new ligands for orphan GPCRs emerging as critical players in various inflammatory diseases. The potential candidates are tested and characterized in cell-based signaling assays and potentially animal-based disease models. The goal is to find compounds with druggable properties for clinical evaluation.
Structural biology of large signaling complexes in cancer and neurodegenerative diseases
Besides GPCRs, we also work on other cell surface signaling complexes in collaboration with labs studying cancer immunology and neurodegenerative diseases. We take advantage of our expertise in human membrane protein production, protein complex assembly, and protein engineering to use cryo-EM to determine structures of signaling complexes that regulate the function of macrophages and T cells and Alzheimer's disease (AD)-related proteolytic pathways. The goal is to define molecular mechanisms for the assembly and regulation of those complexes in various disease settings.