Human dopamine signaling pathway induces and facilitates dopamine neurotransmission through the
mesolimbic dopaminergic pathway, which modifies reward-related behaviors and is associated with the
development of many diseases, including schizophrenia, Huntington's disease, cognitive disorders and
Parkinson’s disease. Mounting evidence suggests that this important signaling pathway is constructively
regulated by the dopamine receptors (DRs). Thus, making members of this membrane protein family highly
promising therapeutic targets as supported by both pre-clinical and clinical studies.
Although some agonists of receptors in the human DR (hDR) family members (e.g. for dopamine D1-like
receptors) are being intensively studied for therapeutic intervention, their success has been greatly hampered
due to poor adherence and efficacy, or due to associated side effects. Relatedly, the polypharmacology of
dopamine D1-like receptor and other hDRs have been discovered in recent studies. New knowledge based on
structures of D1-like receptors (D1R and D5R) will not only reveal their signaling mechanisms, but also provide
new understanding that can be exploited to facilitate rational drug design.
hDRs belong to the G protein-coupled receptor (GPCR) family which is notorious for difficulties in generating
diffraction-quality crystals that are essential for the determination of high-resolution structures by X-ray
crystallography. This R&D proposal aims to develop a comprehensive and robust platform for structural and
functional studies of dopamine D1-like receptors and complexes of hDRs with G proteins, for screening high-
affinity nanobodies, antibodies, and ligands targeting these receptors. This platform will involve multiple steps
that are closely interconnected and looped through a forward and backward feedback system. The PI has now
also established strong collaborations with other research groups with different expertise as alternative
approaches, including X-ray free electron laser, Microcrystal Electron Diffraction technique, etc.
Three specific aims are proposed: (1) Structure/function studies of human D1R (hD1R) in the inactive state, (2)
Using X-ray crystallography and computational biology approaches to study the putative active state of hD1R,
and (3) Establishing optimized approaches for determining the structure of complexes of hD1R with G protein
partners using EM imaging. The significance of this study is multi-fold on dopamine signaling pathway and
related drug discovery studies: 1) we will gain insights into dopamine D1-like receptor functionalities and
allosteric modulations, 2) we will be able to screen extensively to identify new high-affinity ligands for hDRs, 3)
characterize the mechanisms of DR signaling and ligand selection between different dopamine receptor
subfamilies, 4) stimulate hDR structure-based drug design, 5) examine hDRs/G protein complex signaling and
reveal the activation mechanism, and 6) pave the road for the application of cryoEM technology on difficult
membrane protein targets in the future.