The function of 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 across the cell membrane to the intracellular compartment and induce complex signaling pathways. We take multiple approaches in structural biology including crystallography and cryo-EM to study the molecular mechanisms underlying signal transduction of membrane-embedded 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 receptor activities in various disease settings.
Structure and pharmacology of G protein-coupled receptors (GPCRs) in inflammation and immunity
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 several groups of GPCRs that regulate the function of macrophages and T cells. They include formyl peptide receptors (FPRs), the C5a receptor, cannabinoid receptors, free fatty acid receptors (FFARs), chemokine receptors, and several orphan GPCRs. Our research aims to uncover the molecular mechanisms by which these GPCRs recognize a variety of peptide and lipid ligands to regulate immune cell chemotaxis, phagocytosis, secretion of inflammatory mediators, and T cell activation and exhaustion. Additionally, we engage in structure-based drug design (SBDD), partnering with experts in computational biology, to develop novel ligands for these 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
In addition to GPCRs, we collaborate with labs specializing in cancer immunology and neurodegenerative diseases to study other cell surface signaling complexes. Leveraging our expertise in human membrane protein production, protein complex assembly, and protein engineering, we employ cryo-EM to elucidate the structures of signaling complexes involved in immune responses and neurodegenerative diseases.