Structure and function of an intermediate GPCR-Gαβγ complex

Unraveling the signaling roles of intermediate complexes is pivotal for G protein-coupled receptor (GPCR) drug development. Despite hundreds of GPCR-Gαβγ structures, these snapshots primarily capture the fully activated end-state complex. Consequently, a comprehensive understanding of the conformational transitions during GPCR activation and the roles of intermediate GPCR-G protein complexes in signaling remain elusive. Guided by a conformational landscape profiled by 19 F quantitative NMR ( 19 F-qNMR) and Molecular Dynamics (MD) simulations, we resolved the structure of an unliganded GPCR-G protein intermediate complex by blocking its transition to the fully activated end-state complex. More importantly, we presented direct evidence that the intermediate GPCR-Gαsβγ complex initiates a rate-limited nucleotide exchange without progressing to the fully activated end-state complex, thereby bridging a significant gap in our understanding the complexity of GPCR signaling. Understanding the roles of individual conformational states and their complexes in signaling efficacy and bias will help us to design drugs that discriminately target a disease-related conformation.

Assembly of SARS-CoV-2 ribonucleosomes by truncated N∗ variant of the nucleocapsid protein

The nucleocapsid (N) protein of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) compacts the RNA genome into viral ribonucleoprotein (vRNP) complexes within virions. Assembly of vRNPs is inhibited by phosphorylation of the N protein serine/arginine (SR) region. Several SARS-CoV-2 variants of concern carry N protein mutations that reduce phosphorylation and enhance the efficiency of viral packaging. Variants of the dominant B.1.1 viral lineage also encode a truncated N protein, termed N∗ or Δ(1-209), that mediates genome packaging despite lacking the N-terminal RNA-binding domain and SR region. Here, we use mass photometry and negative stain electron microscopy to show that purified Δ(1-209) and viral RNA assemble into vRNPs that are remarkably similar in size and shape to those formed with full-length N protein. We show that assembly of Δ(1-209) vRNPs requires the leucine-rich helix of the central disordered region and that this helix promotes N protein oligomerization. We also find that fusion of a phosphomimetic SR region to Δ(1-209) inhibits RNA binding and vRNP assembly. Our results provide new insights into the mechanisms by which RNA binding promotes N protein self-association and vRNP assembly, and how this process is modulated by phosphorylation.

Invasive fungal infection is associated with antibiotic exposure in preterm infants: a multi-centre prospective case-control study

BACKGROUND

Previous antibiotic exposure is an important risk factor for invasive fungal infection (IFI). Antibiotic overexposure is common in lower-income countries; however, multi-centre studies concerning IFI in relation to antibiotic exposure are scarce.

AIM

This prospective, multi-centre matched case-control study explored the correlation of IFI and antibiotic exposure in very preterm infants or very-low-birthweight infants admitted to 23 tertiary hospitals in China between 2018 and 2021.

METHODS

Using a 1:2 matched design for gestational age, birth weight and early-onset sepsis (yes/no), the risk factors between infants diagnosed with IFI and infection-free controls were compared. The antibiotic use rate (AUR) was calculated using calendar days of antibiotic therapy in the 4 weeks preceding IFI onset divided by onset day of IFI.

FINDINGS

In total, 6368 infants were included in the study, of which 90 (1.4%) were diagnosed with IFI. Median AUR, length of antibiotic therapy (LOT) and days of antibiotic therapy (DOT) within the 4 weeks preceding IFI onset were 0.90, 18 days and 30 days, respectively. Multi-variate analysis showed that a 10% increase in AUR, each additional day of DOT and LOT, and each additional day of third-generation cephalosporins and carbapenems were notably associated with IFI.

CONCLUSION

Prolonged antibiotic therapy is common before the onset of IFI, and is an important risk factor, especially the use of third-generation cephalosporins and carbapenems. Antibiotic stewardship should be urgently developed and promoted for preterm infants in order to reduce IFI in lower-income countries such as China.

Reconstitution of the SARS-CoV-2 ribonucleosome provides insights into genomic RNA packaging and regulation by phosphorylation

The nucleocapsid (N) protein of severe acute respiratory syndrome coronavirus 2 is responsible for compaction of the ∼30-kb RNA genome in the ∼90-nm virion. Previous studies suggest that each virion contains 35 to 40 viral ribonucleoprotein (vRNP) complexes, or ribonucleosomes, arrayed along the genome. There is, however, little mechanistic understanding of the vRNP complex. Here, we show that N protein, when combined in vitro with short fragments of the viral genome, forms 15-nm particles similar to the vRNP structures observed within virions. These vRNPs depend on regions of N protein that promote protein-RNA and protein-protein interactions. Phosphorylation of N protein in its disordered serine/arginine region weakens these interactions to generate less compact vRNPs. We propose that unmodified N protein binds structurally diverse regions in genomic RNA to form compact vRNPs within the nucleocapsid, while phosphorylation alters vRNP structure to support other N protein functions in viral transcription.

Symmetry Reduction in a Hyperpolarization-Activated Homotetrameric Ion Channel

Plants obtain nutrients from the soil via transmembrane transporters and channels in their root hairs, from which ions radially transport in toward the xylem for distribution across the plant body. We determined structures of the hyperpolarization-activated channel AKT1 from Arabidopsis thaliana, which mediates K+ uptake from the soil into plant roots. These structures of AtAKT1 embedded in lipid nanodiscs show that the channel undergoes a reduction of C4 to C2 symmetry, possibly to regulate its electrical activation.

Reconstitution of the SARS-CoV-2 ribonucleosome provides insights into genomic RNA packaging and regulation by phosphorylation

The nucleocapsid (N) protein of coronaviruses is responsible for compaction of the ∼30-kb RNA genome in the ∼100-nm virion. Cryo-electron tomography suggests that each virion contains 35-40 viral ribonucleoprotein (vRNP) complexes, or ribonucleosomes, arrayed along the genome. There is, however, little mechanistic understanding of the vRNP complex. Here, we show that N protein, when combined with viral RNA fragments in vitro, forms cylindrical 15-nm particles similar to the vRNP structures observed within coronavirus virions. These vRNPs form in the presence of stem-loop-containing RNA and depend on regions of N protein that promote protein-RNA and protein-protein interactions. Phosphorylation of N protein in its disordered serine/arginine (SR) region weakens these interactions and disrupts vRNP assembly. We propose that unmodified N binds stem-loop-rich regions in genomic RNA to form compact vRNP complexes within the nucleocapsid, while phosphorylated N maintains uncompacted viral RNA to promote the protein's transcriptional function.

The assembly of β-barrel membrane proteins by BAM and SAM

Gram-negative bacteria, mitochondria, and chloroplasts all possess an outer membrane populated with a host of β-barrel outer-membrane proteins (βOMPs). These βOMPs play crucial roles in maintaining viability of their hosts, and therefore, it is essential to understand the biogenesis of this class of membrane proteins. In recent years, significant structural and functional advancements have been made toward elucidating this process, which is mediated by the β-barrel assembly machinery (BAM) in Gram-negative bacteria, and by the sorting and assembly machinery (SAM) in mitochondria. Structures of both BAM and SAM have now been reported, allowing a comparison and dissection of the two machineries, with other studies reporting on functional aspects of each. Together, these new insights provide compelling support for the proposed budding mechanism, where each nascent βOMP forms a hybrid-barrel intermediate with BAM/SAM in route to its biogenesis into the membrane. Here, we will review these recent studies and highlight their contributions toward understanding βOMP biogenesis in Gram-negative bacteria and in mitochondria. We will also weigh the evidence supporting each of the two leading mechanistic models for how BAM/SAM function, and offer an outlook on future studies within the field.

Silencing of ATPase family AAA domain-containing protein 2 inhibits migration and invasion of colorectal cancer cells

Colorectal cancer is one of the most common malignant tumors with a high rate of distant metastasis, postoperative recurrence and mortality. ATPase family AAA domain-containing protein 2 (ATAD2), a member of ATPase family, is highly expressed in various cancers, including colorectal cancer. However, whether ATAD2 plays a role in the migration and invasion of colorectal cancer cells remains unknown. In this study, we established ATAD2 knockdown in colorectal cancer cell lines by RNA interference and found that silencing of ATAD2 inhibited the migration and invasion ability of Caco-2 and SW-480 cells. Moreover, ATAD2 silencing suppressed epithelial-mesenchymal transition (EMT), and reduced the expression and enzymatic activity of matrix metalloproteinases (MMPs) in Caco-2 and SW-480 cells. In summary, our results suggest that silencing of ATAD2 inhibits migration and invasion of colorectal cancer cells by suppressing EMT and decreasing the activity of MMPs. Hence, ATAD2 could be considered as a novel molecular marker of metastatic colorectal cancer, and it may provide new insights for clinical diagnosis and treatment of colorectal cancer.

Correlations of MC4R and MSH2 expression with obesity in colon cancer patients

OBJECTIVE

To investigate the correlations of MC4R and MSH2 with adult obesity, a total of 46 patients with early-stage colon cancer were treated in our hospital between February 2008 and February 2009 and were enrolled.

PATIENTS AND METHODS

Venous blood was regularly drawn from subjects of the observation group and 48 healthy subjects for 6 years. Expression levels of MC4R and MSH2 genes were tested using quantitative polymerase chain reaction analyses, and the ensuing proteins were determined using enzyme-linked immunosorbent assays and Western blotting and immunohistochemical analyses. Finally, correlations with body mass index (BMI) and the presence of colon cancer were identified using multivariate analyses.

RESULTS

Compared with the control group, MSH2 mRNA and protein expression increased significantly over time (p < 0.05) in patients with colon cancer. Moreover, MSH2 expression was correlated with colon cancer progression, and MC4R mRNA and protein expression increase concurrently in comparison with the control group (p < 0.05). Also, the mean BMI among patients with colon cancer was 30.8, whereas that among control subjects was only 21.4. These data indicate a relationship between BMI and colon cancer.

CONCLUSIONS

Expression of MSH2 in patients with colon cancer may promote the expression of the obesity gene MC4R, potentially contributing to body weight gains.

Defective expression of regulatory B cells in iodine-induced autoimmune thyroiditis in non-obese diabetic H-2(h4) mice

INTRODUCTION

The ability of B cells to negatively regulate cellular immune responses and inflammation has been described. The regulatory B (Breg) cells with the unique CD1d(hi)CD5(+)CD19(+) phenotype and the capacity to produce IL-10 are potent negative regulators of inflammation and autoimmunity in several in vivo mouse models of autoimmune disease.

AIM

To investigate whether Breg cell deficiency participates in autoimmune thyroiditis (AIT) in an animal model.

MATERIALS AND METHODS

Non-obese diabetic (NOD).H-2(h4) mice at 4 weeks of age were randomly divided into control and iodine-treated groups; the iodine-treated group received sterile water containing 0.005 % NaI for 10 or 20 weeks. The percentage of CD1d(hi)CD5(+)CD19(+) Bregs, CD4(+)CD25(+)FoxP3(+) regulatory T cells (Treg) and CD4(+)IL17(+) T helper 17 cells (Th17) in splenic mononuclear cells was detected by multicolor flow cytometry. The expression of IL-10 mRNA and TGF-β mRNA in splenocytes was measured by real-time RT-PCR.

RESULTS

NOD.H-2(h4) mice spontaneously develop anti-thyroglobulin autoantibodies and intrathyroidal lymphocyte infiltration when supplied with iodine in drinking water. Mice with AIT had a decreased CD1d(hi)CD5(+)CD19(+) Breg subset and reduced IL-10 mRNA expression in splenocytes compared with controls (p < 0.05) and maintained relatively low levels during the development of thyroiditis. The proportion of Breg cells was negatively correlated with the proportion of Th17 cells, but positively correlated with CD4(+)CD25(+)FoxP3(+) Treg cells in splenocytes (All p < 0.05).

CONCLUSIONS

The defective expression of Breg cells combined with impaired Treg cells and enhanced Th17 cells might play an important role in the development of iodine-induced AIT in NOD.H-2(h4) mice.

Heterogeneous processing and zona pellucida binding activity of pig zonadhesin

Zonadhesin is a mosaic protein in sperm membrane fractions that binds directly and in a species-specific manner to the extracellular matrix (zona pellucida) of the oocyte. The active form of pig zonadhesin from capacitated, epididymal spermatozoa comprises two covalently associated polypeptide chains of M(r) 105,000 (p105) and M(r) 45,000 (p45). Here we report detection and characterization of multiple zonadhesin isoforms in freshly ejaculated cells. Antibodies to the predicted von Willebrand D0-D1, D1, and D3 domains of pig zonadhesin recognized p105, p45, and additional M(r) 60,000-90,000 polypeptides in particulate fractions of uncapacitated cells. Although the p105/45 form constituted a minority of all zonadhesin forms in sperm membrane fractions, it was the predominant form capable of binding to the pig zona pellucida. Zonadhesin-binding sites were distributed over the entire zona pellucida. Anion exchange chromatography resolved active, p105/45 zonadhesin from the p60-90 inactive forms. Without disulfide bond reduction some zonadhesin was M(r) > or = 300,000, including M(r) 300,000 and 900,000 proteins comprising in part multimers of p105/45. The multimeric forms did not bind the zona pellucida as avidly as did the p105/45 monomer. Expressed D1 and D3 domain fragments containing the CG(L/V)CG sequence motif spontaneously formed multimers at -246 mV E(h) in vitro. Double Cys --> Ser mutants of the D1 fragment formed multimers with the same apparent kinetics as the wild type protein. Zonadhesin localized to the apical head of pig spermatozoa. We conclude that a heterogeneous combination of specific proteolysis and intermolecular disulfide bond formation in the sperm head generates multiple forms of zonadhesin with differing avidities for the zona pellucida.

Stability of luteinizing hormone releasing hormone: effects of pH, temperature, pig skin, and enzyme inhibitors

The purpose of this investigation was to determine the stability of luteinizing hormone releasing hormone (LHRH) as a function of solution pH, temperature, and pig skin with and without enzyme inhibitors. LHRH, incubated with a 0.1 M phosphate buffer (pH 2.5-8.1), pig skin, and pig skin with enzyme inhibitors, was analyzed using reversed-phase high performance liquid chromatography. The solution's pH affected the rate constants of LHRH, following apparent first-order kinetics. Maximum stability was achieved at pH 6.05. Therefore, the effect of various temperatures (i.e., 65, 75, 80, and 90 degrees C) was studied on the stability of LHRH at pH 6.05. The activation energy for the overall reaction was 23.4 kcal/mol at pH 6.05. The shelf-life of LHRH at 25 degrees C and pH 6.05, calculated using the Arrhenius equation, was approximately 4 years. The rate constant of LHRH in the skin (area: 9 cm2; thickness: 0.5 mm) was 0.167 hr-1. Out of three inhibitors (i.e., aprotinin, bestatin, and leupeptin), bestatin had the best stabilizing effect on the degradation of LHRH by the skin. The rate constant of LHRH in the presence of bestatin was 0.082 hr-1. Sixty percent of LHRH was found to be degraded in the skin within 5 hr in the absence of enzyme inhibitors, whereas only 33% of LHRH was degraded in the presence of bestatin (an aminopeptidase inhibitor).

Application of solid-phase microextraction to the recovery of explosives and ignitable liquid residues from forensic specimens

A current review of the application of solid-phase microextraction (SPME) to the analysis of ignitable liquids and explosive residues is presented along with experimental results demonstrating the relative effects of controllable variables. Variables discussed include fiber chemistry, adsorption and desorption temperatures, extraction and desorption times, fiber sampling placement (direct, headspace, and partial headspace) and matrix effects, including water content. SPME is shown to be an inexpensive, rapid and sensitive method for the analysis of ignitable liquids and high explosives residues from solid debris samples and from aqueous samples. Explosives are readily detected at parts per trillion concentrations and ignitable liquids are reproducibly detected at levels below those using conventional methods.

Effect of buffer pH, buffer concentration and skin with or without enzyme inhibitors on the stability of [Arg(8)]-vasopressin

The stability of [Arg(8)]-vasopressin (AVP) as a function of buffer pH, buffer concentration, salt concentration, temperature, and skin with and without enzyme inhibitors was investigated. AVP was analyzed by reverse-phase high-performance liquid chromatography. The results indicated that the buffer's pH affected the degradation rate of AVP. Buffer ions (H(2)PO(4)(-) and HPO(4)(2-)) and salt concentrations had no effect on the degradation of AVP. Maximum stability was achieved at pH 3.35 among pH values tested. The activation energy for the overall reaction was 21.5 kcal mol(-1) at pH 3.35. From the Arrhenius equation, the shelf-life of AVP at 25 degrees C and pH 3.35 was calculated to be 1.38 years. The degradation rate of AVP in the skin (area: 9 cm(2), thickness: 0.5 mm) was 0.22 h(-1). Bestatin (an aminopeptidase inhibitor) had the best stabilizing effect on the degradation of AVP by skin among the three enzyme inhibitors (i.e. aprotinin, bestatin, and leupeptin) studied. The degradation rate of AVP in the skin was reduced to 0. 059 h(-1) in the presence of bestatin in comparison with no inhibitor (0.22 h(-1)).

[Determination of trace arsenic using GFAAS with metal-coated graphite tube]

The sensitivity, precision and disturbance-resisting property were studied by using metal-coated graphite tube for electrically heated atomic absorption spectrometry. The surface characteristic of the metal-coated graphite tube was studied by using X-ray diffraction meter and scanning electron microscope. The mechanism of satisfactory performance was discussed.