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As a large family of membrane proteins crucial for bacterial physiology and virulence, the Multiple Peptide Resistance Factors (MprFs) utilize two separate domains to synthesize and translocate aminoacyl phospholipids to the outer leaflets of bacterial membranes. The function of MprFs enables Staphylococcus aureus and other pathogenic bacteria to acquire resistance to daptomycin and cationic antimicrobial peptides. Here we present cryo-electron microscopy structures of MprF homodimer from Rhizobium tropici ( Rt MprF) at two different states in complex with lysyl-phosphatidylglycerol (LysPG). Rt MprF contains a membrane-embedded lipid-flippase domain with two deep cavities opening toward the inner and outer leaflets of the membrane respectively. Intriguingly, a hook-shaped LysPG molecule is trapped inside the inner cavity with its head group bent toward the outer cavity which hosts a second phospholipid-binding site. Moreover, Rt MprF exhibits multiple conformational states with the synthase domain adopting distinct positions relative to the flippase domain. Our results provide a detailed framework for understanding the mechanisms of MprF-mediated modification and translocation of phospholipids. The Multiple Peptide Resistance Factors (MprFs) utilize two separate domains to synthesize and translocate aminoacyl phospholipids to the outer leaflets of bacterial membranes. Here authors present cryo-electron microscopy structures of MprF homodimer from Rhizobium tropici ( Rt MprF) at two different states in complex with lysyl-phosphatidylglycerol (LysPG).

G-protein-coupled receptors (GPCRs) are a class of integral membrane proteins that detect environmental cues and trigger cellular responses. Deciphering the functional states of GPCRs induced by various ligands has been one of the primary goals in the field. Here we developed an effective universal method for GPCR cryo-electron microscopy structure determination without the need to prepare GPCR-signaling protein complexes. Using this method, we successfully solved the structures of the β 2 -adrenergic receptor (β 2 AR) bound to antagonistic and agonistic ligands and the adhesion GPCR ADGRL3 in the apo state. For β 2 AR, an intermediate state stabilized by the partial agonist was captured. For ADGRL3, the structure revealed that inactive ADGRL3 adopts a compact fold and that large unusual conformational changes on both the extracellular and intracellular sides are required for activation of adhesion GPCRs. We anticipate that this method will open a new avenue for understanding GPCR structure‒function relationships and drug development. A fusion and glue platform was developed to determine the cryo-EM structures of GPCRs in diverse states ranging from β2-adrenergic receptors to adhesion receptors.

Adrenergic receptors (ARs) and muscarinic acetylcholine receptors (mAChRs) are essential G protein-coupled receptors (GPCRs) that regulate a wide range of physiological processes. Despite their significance, developing subtype-selective modulators for these receptors has been a formidable challenge due to the high structural and sequence similarities within their subfamilies. In this study, we elucidated the recognition and regulatory mechanisms of ARs and mAChRs by muscarinic toxin 3 (MT3), a cross-reactive ligand derived from snake venom. By leveraging the distinct toxin-receptor interfaces, we engineer a panel of toxin variants capable of selectively modulating α2A and M 4 AChR using computational design and directed evolution. These subtype-selective toxins not only provide valuable tools for basic research but also hold therapeutic potential for diseases associated with these GPCRs. This study further underscores the effectiveness of structure-guided approaches in transforming venom-derived scaffolds into receptor-specific modulators. Adrenergic and muscarinic receptors are key GPCRs involved in vital functions. Here, the authors engineer toxin variants that selectively target α2A and M4AChR, offering new tools and therapeutic leads through a structure-guided design strategy.

The formyl peptide receptor 1 (FPR1) is primarily responsible for detection of short peptides bearing N-formylated methionine (fMet) that are characteristic of protein synthesis in bacteria and mitochondria. As a result, FPR1 is critical to phagocyte migration and activation in bacterial infection, tissue injury and inflammation. How FPR1 distinguishes between formyl peptides and non-formyl peptides remains elusive. Here we report cryo-EM structures of human FPR1-Gi protein complex bound to S. aureus -derived peptide fMet-Ile-Phe-Leu (fMIFL) and E. coli -derived peptide fMet-Leu-Phe (fMLF). Both structures of FPR1 adopt an active conformation and exhibit a binding pocket containing the R201 5.38 XXXR205 5.42 (RGIIR) motif for formyl group interaction and receptor activation. This motif works together with D106 3.33 for hydrogen bond formation with the N-formyl group and with fMet, a model supported by MD simulation and functional assays of mutant receptors with key residues for recognition substituted by alanine. The cryo-EM model of agonist-bound FPR1 provides a structural basis for recognition of bacteria-derived chemotactic peptides with potential applications in developing FPR1-targeting agents. Detection of invading bacteria is key to immunity. Here, the authors report cryo-electron microscopy structures of agonist-bound formyl peptide receptor 1 (FPR1), that reveal structural basis for recognition of bacteria-derived formyl peptides.

The subcortical maternal complex (SCMC) is essential for safeguarding female fertility in mammals. Assembled in oocytes, the SCMC maintains the cleavage of early embryos, but the underlying mechanism remains unclear. Here, we report that 14-3-3, a multifunctional protein, is a component of the SCMC. By resolving the structure of the 14-3-3-containing SCMC, we discover that phosphorylation of TLE6 contributes to the recruitment of 14-3-3. Mechanistically, during maternal-to-embryo transition, the SCMC stabilizes 14-3-3 protein and contributes to the proper control of CDC25B, thus ensuring the activation of the maturation-promoting factor and mitotic entry in mouse zygotes. Notably, the SCMC establishes a conserved molecular link with 14-3-3 and CDC25B in human oocytes/embryos. This study discloses the molecular mechanism through which the SCMC regulates the cell cycle in early embryos and elucidates the function of the SCMC in mammalian early embryogenesis. The subcortical maternal complex (SCMC) maintains cleavage of early embryos. Here the authors identify 14-3-3 as a component of the SCMC and show that phosphorylation of TLE6 contributes to 14-3-3 recruitment and stabilization, ensuring mitotic entry in mouse zygotes.

Mas-related G-protein-coupled receptors X1-X4 (MRGPRX1-X4) are 4 primate-specific receptors that are recently reported to be responsible for many biological processes, including itch sensation, pain transmission, and inflammatory reactions. MRGPRX1 is the first identified human MRGPR, and its expression is restricted to primary sensory neurons. Due to its dual roles in itch and pain signaling pathways, MRGPRX1 has been regarded as a promising target for itch remission and pain inhibition. Here, we reported a cryo-electron microscopy (cryo-EM) structure of G q -coupled MRGPRX1 in complex with a synthetic agonist compound 16 in an active conformation at an overall resolution of 3.0 Å via a NanoBiT tethering strategy. Compound 16 is a new pain-relieving compound with high potency and selectivity to MRGPRX1 over other MRGPRXs and opioid receptor. MRGPRX1 was revealed to share common structural features of the G q -mediated receptor activation mechanism of MRGPRX family members, but the variable residues in orthosteric pocket of MRGPRX1 exhibit the unique agonist recognition pattern, potentially facilitating to design MRGPRX1-specific modulators. Together with receptor activation and itch behavior evaluation assays, our study provides a structural snapshot to modify therapeutic molecules for itch relieving and analgesia targeting MRGPRX1.

Yellow fever virus (YFV) infections can cause severe diseases in humans, resulting in mass casualties in Africa and the Americas each year. Secretory NS1 (sNS1) is thought to be used as a diagnostic marker of flavivirus infections, playing an essential role in the flavivirus life cycle, but little is known about the composition and structure of YFV sNS1. Here, we present that the recombinant YFV sNS1 exists in a heterogeneous mixture of oligomerizations, predominantly in the tetrameric form. The cryoEM structures show that the YFV tetramer of sNS1 is stacked by the hydrophobic interaction between β-roll domains and greasy fingers. According to the 3D variability analysis, the tetramer is in a semi-stable state that may contain multiple conformations with dynamic changes. We believe that our study provides critical insights into the oligomerization of NS1 and will aid the development of NS1-based diagnoses and therapies.

The chemotaxis of CD4 + type 1 helper cells and CD8 + cytotoxic lymphocytes, guided by interferon-inducible CXC chemokine 9–11 (CXCL9–11) and CXC chemokine receptor 3 (CXCR3), plays a critical role in type 1 immunity. Here we determined the structures of human CXCR3–DNG i complexes activated by chemokine CXCL11, peptidomimetic agonist PS372424 and biaryl-type agonist VUF11222, and the structure of inactive CXCR3 bound to noncompetitive antagonist SCH546738. Structural analysis revealed that PS372424 shares a similar orthosteric binding pocket to the N terminus of CXCL11, while VUF11222 buries deeper and activates the receptor in a distinct manner. We showed an allosteric binding site between TM5 and TM6, accommodating SCH546738 in the inactive CXCR3. SCH546738 may restrain the receptor at an inactive state by preventing the repacking of TM5 and TM6. By revealing the binding patterns and the pharmacological properties of the four modulators, we present the activation mechanisms of CXCR3 and provide insights for future drug development. The authors present the structures of chemokine receptor CXCR3 complexed with agonists CXCL11, PS372424 and VUF11222 and antagonist SCH546738, providing a basis for the ligand recognition and activation mechanism of CXCR3.

Intracellular S1P promotes cellular proliferation, whereas plasma S1P facilitates immune cell trafficking, regulates angiogenesis, and helps to maintain vascular integrity.1 Due to the amphipathic property, S1P cannot diffuse freely but has to be transported across the cell membrane through active transport.1 In the past two decades, several S1P transporters have been identified, including two major facilitator superfamily (MFS) members: Among these transporters, Spns2 is the first identified and the most extensively studied.2 Here, we reported two cryo-electron microscopy (EM) structures of human Spns2 in inward-open conformations bound to S1P or inhibitor 16d. Human Spns2 is a classical MFS member with twelve transmembrane (TM) helices and a molecular weight of ~58 kDa, which is small for cryo-EM analysis. [...]we fused a PGS (Pyrococcus abyssi glycogen synthase) protein (UniProt ID: Q9V2J8) between F222 and T223 on intracellular loop 2 of Spns2 (named Spns2fusion) to enlarge the protein size to facilitate cryo-EM structure determination (Supplementary information, Fig.