Activation of the human chemokine receptor CX3CR1 regulated by cholesterol.

As the only member of the CX3C chemokine receptor subfamily, CX3CR1 binds to its sole endogenous ligand CX3CL1, which shows notable potential as a therapeutic target in atherosclerosis, cancer, and neuropathy. However, the drug development of CX3CR1 is hampered partially by the lack of structural information. Here, we present two cryo-electron microscopy structures of CX3CR1-Gi1 complexes in ligand-free and CX3CL1-bound states at 2.8- and 3.4-Å resolution, respectively. Together with functional data, the structures reveal the key factors that govern the recognition of CX3CL1 by both CX3CR1 and US28. A much smaller conformational change of helix VI upon activation than previously solved class A GPCR-Gi complex structures is observed in CX3CR1, which may correlate with three cholesterol molecules that play essential roles in conformation stabilization and signaling transduction. Thus, our data deepen the understanding of cholesterol modulation in GPCR (G protein-coupled receptor) signaling and provide insights into the diversity of G protein coupling.

Receptor-specific recognition of NPY peptides revealed by structures of NPY receptors.

In response to three highly conserved neuropeptides, neuropeptide Y (NPY), peptide YY, and pancreatic polypeptide (PP), four G protein-coupled receptors mediate multiple essential physiological processes, such as food intake, vasoconstriction, sedation, and memory retention. Here, we report the structures of the human Y1, Y2, and Y4 receptors in complex with NPY or PP, and the Gi1 protein. These structures reveal distinct binding poses of the peptide upon coupling to different receptors, reflecting the importance of the conformational plasticity of the peptide in recognizing the NPY receptors. The N terminus of the peptide forms extensive interactions with the Y1 receptor, but not with the Y2 and Y4 receptors. Supported by mutagenesis and functional studies, subtype-specific interactions between the receptors and peptides were further observed. These findings provide insight into key factors that govern NPY signal recognition and transduction, and would enable development of selective drugs.

[Analysis of Transfusion Therapy Effectiveness in Patients with Myelodysplastic Syndrome].

OBJECTIVE: To investigate the transfusion effectiveness of suspended leucocyte depleted red blood cells (sld RBC) and fresh and irradiated apheresis platelets (fia Plt) in patients with myelodysplastic syndromes (MDS), and to explore the causes and mechanisms of ineffective platelet transfusion in patients with MDS. METHODS: Clinical data of 37 patients with confirmed MDS (WHO standard) such as the sex, age, Hb levels, Plt count, hemorrhage and coagulation functions, TEG and so on, were retrospectively analyzed. RESULTS: Among the 37 patients, 15 patients (40.5%) received only sld RBC transfusion, 9 patients (24.3%) received only fia Plt transfusion, and 13 patients (35.1%) received both transfusion. Among the 15 patients with only red blood cell transfusion, 3 patients were ineffective and the ineffectual transfusion rate was 20.0%. Among the 9 patients with only received platelet transfusion, 5 patients were ineffective and the ineffectual transfusion rate was 55.6%, there were significant statistical differences between the two groups (P﹤0.01). The red blood cell transfusion ineffective were 3 patients (23.1%) , the platelet transfusion ineffective were 8 patients (61.5%) and the both transfusion ineffective were 2 patients (15.4%) among the patients both transfusion . The positive rate of platelet antibody in MDS patients with ineffective platelet transfusion was 23.1%. Compared with the normal control group, Human P selectin (P-SelectinCD62P) (P＜0.001) and human anti-thrombin 3 antibody (AT-III Ab) (P＜0.001) significantly increased and human tissue factor pathway inhibitor (TFPI) significantly decreased (P＜0.05) in MDS patients with ineffective platelet transfusion. CONCLUSION: In the process of component transfusion for MDS patients, compared with the transfusion of red blood cells, the inefficiencies of platelet transfusion significantly increased, mainly due to the disorder of blood coagulation and the generation of platelet antibodies in MDS patients with ineffective platelet transfusion. Compared with the normal control group, human P selectin and human anti-thrombin 3 antibody significantly increase and human tissue factor pathway inhibitor significantly decreases in MDS patients with ineffective platelet transfusion. Human P selectin, human anti-thrombin 3 antibody and human tissue factor pathway inhibitor in molecular markers and fibrinolytic markers can be used as indicators of platelet transfusion time and efficiency in patients with MDS.

Cryo-electron microscopy structure of the glucagon receptor with a dual-agonist peptide.

Unimolecular dual agonists of the glucagon (GCG) receptor (GCGR) and glucagon-like peptide-1 receptor (GLP-1R) are a new class of drugs that are potentially superior to GLP-1R-specific agonists for the management of metabolic disease. The dual-agonist, peptide 15 (P15), is a glutamic acid 16 analog of GCG with GLP-1 peptide substitutions between amino acids 17 and 24 that has potency equivalent to those of the cognate peptide agonists at the GCGR and GLP-1R. Here, we have used cryo-EM to solve the structure of an active P15-GCGR-Gs complex and compared this structure to our recently published structure of the GCGR-Gs complex bound to GCG. This comparison revealed that P15 has a reduced interaction with the first extracellular loop (ECL1) and the top of transmembrane segment 1 (TM1) such that there is increased mobility of the GCGR extracellular domain and at the C terminus of the peptide compared with the GCG-bound receptor. We also observed a distinct conformation of ECL3 and could infer increased mobility of the far N-terminal His-1 residue in the P15-bound structure. These regions of conformational variance in the two peptide-bound GCGR structures were also regions that were distinct between GCGR structures and previously published peptide-bound structures of the GLP-1R, suggesting that greater conformational dynamics may contribute to the increased efficacy of P15 in activation of the GLP-1R compared with GCG. The variable domains in this receptor have previously been implicated in biased agonism at the GLP-1R and could result in altered signaling of P15 at the GCGR compared with GCG.