Structural Basis of Psychedelic LSD Recognition at Dopamine D1 Receptor

Biochemistry Biophysics Life Sciences Pharmacy Medicine Cell Biology
psychedelic LSD dopamine D1 receptor structural biology GPCR

Structural Basis of LSD Recognition in Dopamine D1 Receptors

Research Background and Problem Statement

LSD (lysergic acid diethylamide) is a well-known hallucinogen that primarily exerts profound cognitive and perceptual effects by acting on various neurotransmitter receptors, including serotonin (5-HT) receptors and dopamine receptors. The 5-HT2A and 5-HT2B receptors are major targets of LSD, and researchers have extensively studied the interactions between LSD and these receptors over the years. However, even though dopamine receptors, especially D1-type receptors (DRD1), are considered significant targets of LSD, the specific binding dynamics and mechanisms of receptor structure remain unclear. D1 receptors, the most abundant dopamine receptors in the central nervous system, are involved in memory, learning, and cognitive functions. Further elucidating the recognition and binding mechanisms of LSD on DRD1 is crucial for understanding its hallucinogenic effects and potential therapeutic applications.

Research Source and Publication Status

This study was collaboratively conducted by Luyu Fan, Youwen Zhuang, Hongyu Wu, and others from several leading research institutions in China, including the Key Laboratory of System Health Science of the Chinese Academy of Sciences, the Center for Structural Pharmacology of the Shanghai Institute of Materia Medica, and the iHuman Institute of ShanghaiTech University. The paper was published in the October 2024 issue of the journal “Neuron,” presenting a cryo-electron microscopy (Cryo-EM) structural analysis of LSD binding with DRD1 and exploring the impact of different signaling proteins on receptor dynamics.

Research Process and Experimental Methods

1. Research Design

The study mainly utilized cryo-electron microscopy structural analysis combined with nanobody-assisted techniques to thoroughly investigate the binding structure of LSD and the DRD1 receptor. The core steps of the study included:

  • Nanobody Design and Screening: Initially, the research team designed a nanobody NBA3 mimicking the β-arrestin protein by modifying the amino acid sequence in the CDR3 region, enabling it to bind with DRD1 and stabilize its active conformation.
  • Expression and Purification of the LSD-DRD1 Complex: Using protein engineering techniques, the research team fused the NBA3 to the C-terminus of DRD1 and introduced stabilizing mutations to enhance the protein expression and purification efficiency.
  • Cryo-Electron Microscopy Structure Analysis: Through cryo-electron microscopy, researchers successfully resolved the structure of the LSD-DRD1 complex at a resolution of 3.6 Å. Another agonist, PF6142, was used to further improve structure resolution, achieving a high-resolution structure at 3.0 Å.
  • Molecular Dynamics Simulation and Binding Kinetics Measurement: The research team utilized molecular dynamics simulation and isotope binding experiments to study the binding pattern and dissociation kinetics of LSD and analyzed the impact of different transducer proteins (G proteins and β-arrestins) on receptor stability.

2. Key Experimental Findings

During nanobody screening, NBA3 was demonstrated to stabilize the binding site of β-arrestin on DRD1, exhibiting pharmacological properties similar to β-arrestins. Structural analysis revealed significant differences in the binding mode of LSD on DRD1 compared to its binding mode on 5-HT2 receptors. On DRD1, the ergoline ring of LSD is positioned closer to TM4 (transmembrane helix 4) and away from TM5, resulting in a unique conformation that facilitates rapid LSD dissociation.

The study further revealed that the flexibility of the ECL2 (extracellular loop 2) region of DRD1 plays a crucial role in the rapid dissociation of LSD. However, when G protein binds, the conformation of ECL2 becomes stable, significantly slowing LSD dissociation.

Main Research Results

1. Unique Binding Mode of LSD on DRD1

LSD’s binding to DRD1 involves the formation of a conserved salt bridge, with D103^3.32 providing a pivotal anchoring role through its interaction with the basic nitrogen of LSD’s ergoline system. Compared to its binding modes in 5-HT2A and 5-HT2B receptors, LSD exhibits greater rotational freedom on DRD1. This rotational adjustment helps LSD avoid spatial conflict with the K2.61 residue on DRD1, thereby affecting receptor signal transduction.

2. Flexibility of ECL2 and LSD Dissociation Dynamics

The study showed that the flexibility of the ECL2 region of DRD1 is the primary reason for the extremely fast dissociation rate of LSD. The introduction of an S188^45.52L mutation results in a more stable ECL2 conformation, significantly extending the residence time of LSD on the receptor. This finding unveils the critical role of ECL2 in regulating ligand dissociation kinetics.

3. G Protein’s Role in Receptor Conformation Stability

The study found that G protein binding stabilizes the outward movement of DRD1’s TM5 and TM6 helices while also stabilizing the conformation of ECL2. This stability leads to significantly reduced dissociation rates of LSD and the antagonist SCH23390 in the presence of G proteins. Molecular dynamics simulations also supported the contribution of G proteins to ECL2 stability.

Research Conclusions and Significance

Through structural and dynamic analysis, this study for the first time unveiled the unique binding mode of LSD on dopamine D1 receptors and the molecular mechanism for its rapid dissociation. The research also demonstrated the key role of G proteins in stabilizing receptor active conformation and extending ligand residence time. These discoveries provide important structural foundations for further research into GPCR (G protein-coupled receptor) dynamic mechanisms and offer new perspectives for precision drug design targeting DRD1.

Research Highlights and Innovations

  • Innovative Application of Nanobody NBA3: The NBA3 nanobody designed by the research team simulates the action of β-arrestins, significantly enhancing the resolution of structural analysis and revealing the influence of transducer proteins on receptor conformation.
  • First Resolution of LSD-DRD1 Binding Structure: This study, for the first time, resolved the binding structure of LSD and DRD1 using cryo-electron microscopy, providing crucial structural insight into the mechanism of LSD’s action on dopamine receptors.
  • Revealing G Protein’s Impact on Receptor Stability: The research found that G proteins not only stabilize DRD1’s TM5 and TM6 helices but also extend ligand residence time by stabilizing ECL2 conformation. This mechanism holds significant potential for application in GPCR drug design.

Research Significance and Outlook

This study deepens the understanding of LSD’s recognition and binding mechanisms on dopamine D1 receptors, unveils new mechanisms of GPCR dynamic regulation, and provides a scientific basis for exploring the hallucinogenic mechanisms and potential therapeutic applications of LSD. Future research can leverage these structural insights to develop novel drug molecules that selectively modulate DRD1-mediated signaling pathways for treating neuropsychiatric disorders.

This research not only offers new insights to the GPCR field but also provides valuable references for future structural biology and medicinal chemistry studies.