Chongyuan Wang

GPR99 holds promise as a potential therapeutic target for inflammatory diseases. GPR99 exhibits marked basal activity when coupled with the G _q protein, its activation mechanism remains elusive. In this study, we determine the high-resolution structure of the human GPR99 in complex with the heterotrimeric miniG _q in the ligand-free state using cryo-electron microscopy (cryo-EM). Our structural analysis and functional experiments reveal that the second extracellular loop (ECL2) of GPR99 occupies the orthosteric binding pocket, thereby promoting receptor self-activation. Moreover, we observe structural water molecules forming an extended polar network that connects ECL2 and the binding pocket, intricately linking these elements to the receptor’s functional activity. Structure-based mutagenesis experiments further validate the critical role of ECL2 in intracellular signal transduction of GPR99, offering a structural basis for exploring its function under physiological or pathological conditions. Additionally, these findings also provide a crucial theoretical framework for the design of drugs targeting GPR99.

Cysteinyl leukotriene receptor CysLT2R, which is activated by the endogenous cysteinyl leukotrienes (CysLTs) LTC4, LTD4, and LTE4, has emerged as a potential therapeutic target due to the involvement in various inflammatory diseases. Accumulating evidence indicates that CysLT2R is also involved in the pathogenesis of cardiovascular diseases and contribute to tumor progression in cancer. However, the structural basis underlying the ligand recognition and the receptor activation remains to be elucidated. Here, we present two cryo-electron microscopy (cryo-EM) structures of the human CysLT2R-G _q complexes bound to LTC4 and LTD4. CysLTs are characterized as ago-allosteric modulators (ago-PAMs) of CysLT2R. Our structures reveal that CysLTs are recognized by a lipid-facing pocket above intracellular loop 2 (ICL2) near the cytoplasmic side of the receptor. Furthermore, a noncanonical activation mechanism exists between the allosteric binding pocket and the G _q -binding site. Our findings provide comprehensive insights into the recognition of CysLTs and G _q protein signaling transduction by CysLT2R, which may facilitate rational design of drugs.

DEK is a highly conserved chromatin-associated oncoprotein that has important roles in regulating chromatin dynamics and stem cell fate. Dysregulation of DEK is associated with stem cell dysfunction and cancers, including acute myeloid leukemia. Despite its importance in chromatin regulation, the structural mechanisms underlying DEK’s interaction with chromatin and its influence on gene regulation remain poorly understood. Here we combined cryogenic electron microscopy (cryo-EM), biochemical and cellular approaches to investigate the molecular mechanisms and functional importance of DEK’s interaction with chromatin. Our cryo-EM structures reveal the structural basis of the DEK–nucleosome interaction. Biochemical and cellular results demonstrate that this interaction is crucial for DEK deposition onto chromatin. Furthermore, our results reveal that DEK safeguards mouse embryonic stem cells from acquiring primitive endoderm fates by modulating the repressive histone mark H3K27me3. Together, our study provides crucial molecular insights into the structure and function of DEK, establishing a framework for understanding its roles in chromatin biology and cell fate determination.

The potassium channel TWIK-2 is crucial for ATP-induced activation of the NLRP3 inflammasome in macrophages. The channel is a member of the two-pore domain potassium (K2P) channel superfamily and an emerging therapeutic target to mitigate severe inflammatory injury involving NLRP3 activation. We report the cryo-EM structure of human TWIK-2. In comparison to other K2P channels, the structure reveals a unique ‘up’ conformation of Tyr111 in the selectivity filter and a SF1-P1 pocket behind the filter that could serve as a binding site for channel modulators. Density for acyl chains is present in fenestrations within the transmembrane region that connect the central cavity of the pore to the lipid membrane. Limited pharmacological tools are available for TWIK-2 despite its importance as a drug target. We show that the small molecule pimozide inhibits TWIK-2 and determine a structure of the channel with pimozide. Pimozide displaces the acyl chains and binds below the selectivity filter to block ion conduction. The drug may access its binding site via the membrane, suggesting that other hydrophobic small molecules could have utility for inhibiting TWIK-2. The work defines the structure of TWIK-2 and provides a structural foundation for development of specific inhibitors with potential utility as anti-inflammatory drugs. Significance Statement: The TWIK-2 potassium channel is a member of the two-pore domain potassium (K2P) channel superfamily and a potential therapeutic target to control severe inflammatory injury involving the NLRP3 inflammasome. We report the cryo-EM structure of the human TWIK-2 channel at 2.85 Å resolution, revealing differences in comparison to other K2P channels. We identify that pimozide, an FDA-approved drug for Tourette syndrome, inhibits TWIK-2. A cryo-EM structure of TWIK-2 in complex with pimozide identifies its binding location and mechanism of inhibition. The work provides a structural foundation for development of specific TWIK-2 inhibitors that have potential therapeutic utility for inflammatory diseases involving NLRP3 activation.

Pentamidine and melarsoprol are primary drugs used to treat the lethal human sleeping sickness caused by the parasite Trypanosoma brucei. Cross-resistance to these two drugs has recently been linked to aquaglyceroporin 2 of the trypanosome (TbAQP2). TbAQP2 is the first member of the aquaporin family described as capable of drug transport; however, the underlying mechanism remains unclear. Here, we present cryo-electron microscopy structures of TbAQP2 bound to pentamidine or melarsoprol. Our structural studies, together with the molecular dynamic simulations, reveal the mechanisms shaping substrate specificity and drug permeation. Multiple amino acids in TbAQP2, near the extracellular entrance and inside the pore, create an expanded conducting tunnel, sterically and energetically allowing the permeation of pentamidine and melarsoprol. Our study elucidates the mechanism of drug transport by TbAQP2, providing valuable insights to inform the design of drugs against trypanosomiasis.

The proton-activated chloride channel ASOR (TMEM206/PAC) permeates anions across cellular membranes in response to acidification, thereby enhancing acid-induced cell death and regulating endocytosis. The molecular mechanisms of pH-dependent control are not understood, in part because structural information for an activated conformation of ASOR is lacking. Here, we reconstitute function from purified protein and present a 3.1-Å-resolution cryo–electron microscopy structure of human ASOR at acidic pH in an activated conformation. The work contextualizes a previous acidic pH structure as a desensitized conformation. Combined with electrophysiological studies and high-resolution structures of resting and desensitized states, the work reveals mechanisms of proton sensing and ion pore gating. Clusters of extracellular acidic residues function as pH sensors and coalesce when protonated. Ensuing conformational changes induce metamorphosis of transmembrane helices to fashion an ion conduction pathway unique to the activated conformation. The studies identify a new paradigm of channel gating in this ubiquitous ion channel.

The proteins MCU and EMRE form the minimal functional unit of the mitochondrial calcium uniporter complex in metazoans, a highly selective and tightly controlled Ca ²⁺ channel of the inner mitochondrial membrane that regulates cellular metabolism. Here we present functional reconstitution of an MCU-EMRE complex from the red flour beetle, Tribolium castaneum , and a cryo-EM structure of the complex at 3.5 Å resolution. Robust Ca ²⁺ uptake is observed into proteoliposomes containing the purified complex and is dependent on EMRE. The structure reveals a tetrameric channel with a single ion pore. EMRE is located at the periphery of the transmembrane domain and associates primarily with the first transmembrane helix of MCU. Coiled coil and juxtamembrane domains within the matrix portion of the complex adopt markedly different conformations than in a structure of a human MCU-EMRE complex, suggesting that the structures represent different conformations of these functionally similar metazoan channels.