Development and Validation of the Nonalcoholic Fatty Liver Disease Familial Risk Score to Detect Advanced Fibrosis: A Prospective, Multicenter Study.

BACKGROUND & AIMS: Nonalcoholic fatty liver disease (NAFLD)-related fibrosis is heritable, but it is unclear how family history may be used to identify first-degree relatives with advanced fibrosis. We aimed to develop and validate a simple risk score to identify first-degree relatives of probands who have undergone assessment of liver fibrosis who are at higher risk of NAFLD with advanced fibrosis. METHODS: This prospective, cross-sectional, familial study consisted of a derivation cohort from San Diego, California, and a validation cohort from Helsinki, Finland. This study included consecutive adult probands (n = 242) with NAFLD and advanced fibrosis, NAFLD without advanced fibrosis, and non-NAFLD, with at least 1 of their first-degree relatives. All included probands and first-degree relatives underwent evaluation of liver fibrosis, the majority by magnetic resonance elastography. RESULTS: A total of 396 first-degree relatives (64% male) were included. The median age and body mass index were 47 years (interquartile range, 32-62 y) and 27.6 kg/m2 (interquartile range, 24.1-32.5 kg/m2), respectively. Age (1 point), type 2 diabetes (1 point), obesity (2 points), and proband with NAFLD and advanced fibrosis (2 points) were predictors of advanced fibrosis among first-degree relatives in the derivation cohort (n = 220) and formed the NAFLD Familial Risk Score. The area under the receiver operator characteristic curve of the NAFLD Familial Risk Score for detecting advanced fibrosis was 0.94 in the validation cohort (n = 176). The NAFLD Familial Risk Score outperformed the Fibrosis-4 index in the validation cohort (area under the receiver operator characteristic curve, 0.94 vs 0.70; P = .02). CONCLUSIONS: The NAFLD Familial Risk Score is a simple and accurate clinical tool to identify advanced fibrosis in first-degree relatives. These data may have implications for surveillance in NAFLD.

Validation of AGA clinical care pathway and AASLD practice guidance for nonalcoholic fatty liver disease in a prospective cohort of patients with type 2 diabetes.

BACKGROUND AND AIMS: Recently, the American Gastroenterological Association and the American Association for the Study of Liver Diseases developed clinical pathways to evaluate populations at high risk for NAFLD. We assessed the diagnostic performance of the new guidance in a well-phenotyped cohort of patients with Type 2 diabetes mellitus (T2DM). APPROACH AND RESULTS: This prospective study enrolled patients age ≥50 years with T2DM. Participants underwent a standardized clinical research visit with MRI and ultrasound-based assessment of liver fat and stiffness and Enhanced Liver Fibrosis (ELF) testing. Of 417 participants (36% men) with T2DM with FIB-4 and MRE data, the prevalence of NAFLD was 64% and 12% had advanced fibrosis (MRE≥3.63 kPa). Applying the American Gastroenterological Association pathway of FIB-4 and vibration-controlled transient elastography, the false negative rate was 3.3% and 18% would qualify for specialty referral. Applying the FIB-4 + ELF American Association for the Study of Liver Diseases pathway, the false negative rate was 4.5%, but 50% would qualify for specialty referral. Applying higher ELF cut points improved the pathway, yielding a similar false negative rate of 4.9% but decreased specialty referral to 27%. CONCLUSION: Validation of the American Gastroenterological Association clinical pathway in a prospectively recruited cohort with T2DM revealed a low false negative rate and avoided specialty referral in a large percentage of patients. The American Association for the Study of Liver Diseases pathway with FIB-4 + ELF resulted in a high rate of specialty referral, which improved with the utilization of higher ELF cut points and may serve as an alternative for primary care and endocrinology clinics without access to vibration-controlled transient elastography.

A knockout-first model of H3f3a gene targeting leads to developmental lethality.

Histone variant H3.3 is encoded by two genes, H3f3a and H3f3b, which can be expressed differentially depending on tissue type. Previous work in our lab has shown that knockout of H3f3b causes some neonatal lethality and infertility in mice, and chromosomal defects in mouse embryonic fibroblasts (MEFs). Studies of H3f3a and H3f3b null mice by others have produced generally similar phenotypes to what we found in our H3f3b nulls, but the relative impacts of the loss of either H3f3a or H3f3b have varied depending on the approach and genetic background. Here we used a knockout-first approach to target the H3f3a gene for inactivation in C57BL6 mice. Homozygous H3f3a targeting produced a lethal phenotype at or before birth. E13.5 null embryos had some potential morphological differences from WT littermates including smaller size and reduced head size. An E18.5 null embryo was smaller than its control littermates with several potential defects including small head and brain size as well as small lungs, which would be consistent with a late gestation lethal phenotype. Despite a reduction in H3.3 and total H3 protein levels, the only histone H3 post-translational modification in the small panel assessed that was significantly altered was the unique H3.3 mark phospho-Serine31, which was consistently increased in null neurospheres. H3f3a null neurospheres also exhibited consistent gene expression changes including in protocadherins. Overall, our findings are consistent with the model that there are differential, cell-type-specific contributions of H3f3a and H3f3b to H3.3 functions in epigenetic and developmental processes.

Risk of advanced fibrosis in first-degree relatives of patients with nonalcoholic fatty liver disease.

BACKGROUNDA pilot, single-center study showed that first-degree relatives of probands with nonalcoholic fatty liver disease (NAFLD) cirrhosis have a high risk of advanced fibrosis. We aimed to validate these findings using 2 independent cohorts from the US and Europe.METHODSThis prospective study included probands with NAFLD with advanced fibrosis, NAFLD without advanced fibrosis, and non-NAFLD, with at least 1 first-degree relative. A total of 396 first-degree relatives - 220 in a derivation cohort and 176 in a validation cohort - were enrolled in the study, and liver fibrosis was evaluated using magnetic resonance elastography and other noninvasive imaging modalities. The primary outcome was prevalence of advanced fibrosis in first-degree relatives.RESULTSPrevalence of advanced fibrosis in first-degree relatives of probands with NAFLD with advanced fibrosis, NAFLD without advanced fibrosis, and non-NAFLD was 15.6%, 5.9%, and 1.3%, respectively (P = 0.002), in the derivation cohort, and 14.0%, 2.6%, and 1.3%, respectively (P = 0.004), in the validation cohort. In multivariable-adjusted logistic regression models, age of ≥50 years (adjusted OR [aOR]: 2.63, 95% CI 1.0-6.7), male sex (aOR: 3.79, 95% CI 1.6-9.2), diabetes mellitus (aOR: 3.37, 95% CI 1.3-9), and a first-degree relative with NAFLD with advanced fibrosis (aOR: 11.8, 95% CI 2.5-57) were significant predictors of presence of advanced fibrosis (all P < 0.05).CONCLUSIONFirst-degree relatives of probands with NAFLD with advanced fibrosis have significantly increased risk of advanced fibrosis. Routine screening should be done in the first-degree relatives of patients with advanced fibrosis.FUNDINGSupported by NCATS (5UL1TR001442), NIDDK (U01DK061734, U01DK130190, R01DK106419, R01DK121378, R01DK124318, P30DK120515, K23DK119460), NHLBI (P01HL147835), and NIAAA (U01AA029019); Academy of Finland grant 309263; the Novo Nordisk, EVO, and Sigrid Jusélius Foundations; and the Innovative Medicines Initiative 2 Joint Undertaking under grant agreement 777377. This Joint Undertaking receives support from the European Union's Horizon 2020 research and innovation program and the EFPIA.

Reciprocal H3.3 gene editing identifies K27M and G34R mechanisms in pediatric glioma including NOTCH signaling.

Histone H3.3 mutations are a hallmark of pediatric gliomas, but their core oncogenic mechanisms are not well-defined. To identify major effectors, we used CRISPR-Cas9 to introduce H3.3K27M and G34R mutations into previously H3.3-wildtype brain cells, while in parallel reverting the mutations in glioma cells back to wildtype. ChIP-seq analysis broadly linked K27M to altered H3K27me3 activity including within super-enhancers, which exhibited perturbed transcriptional function. This was largely independent of H3.3 DNA binding. The K27M and G34R mutations induced several of the same pathways suggesting key shared oncogenic mechanisms including activation of neurogenesis and NOTCH pathway genes. H3.3 mutant gliomas are also particularly sensitive to NOTCH pathway gene knockdown and drug inhibition, reducing their viability in culture. Reciprocal editing of cells generally produced reciprocal effects on tumorgenicity in xenograft assays. Overall, our findings define common and distinct K27M and G34R oncogenic mechanisms, including potentially targetable pathways.

Yeast ENV9 encodes a conserved lipid droplet (LD) short-chain dehydrogenase involved in LD morphology.

Lipid droplets (LDs) have emerged as dynamic and interactive organelles with important roles in lipid metabolism and membrane biogenesis. Here, we report that Saccharomyces cerevisiae Env9 is a novel conserved oxidoreductase involved in LD morphology. Microscopic and biochemical studies confirm localization of tagged Env9 to LDs and implicate its C-terminal hydrophobic domain (aa241-265) in its membrane association and stability. Confocal studies reveal a role for Env9 in LD morphology. Env9 positively affects both formation of large LDs upon overexpression and LD proliferation under poor carbon source. In silico bioinformatic and modeling approaches establish that ENV9 is a widely conserved member of the short-chain dehydrogenase (SDR) superfamily. Bayesian phylogenetic studies strongly support ENV9 as an ortholog of human SDR retinol dehydrogenase 12 (RDH12). Dehydrogenase activity of Env9 was confirmed by in vitro oxidoreductase assays. RDH12 mutations have been linked to Leber Congenital Amaurosis. Similar site-directed point mutations in the predicted Env9 oxidoreductase active site (N146L) or cofactor-binding site (G23-24A) abolished its reductase activity in vitro, consistent with those reported in other retinol dehydrogenases. The same residues were essential for affecting LD size and number in vivo. Taken together, our results implicate oxidoreductase activity of Env9 in its cellular role in LD morphology.

Thyroid Hormone Receptor α Plays an Essential Role in Male Skeletal Muscle Myoblast Proliferation, Differentiation, and Response to Injury.

Thyroid hormone plays an essential role in myogenesis, the process required for skeletal muscle development and repair, although the mechanisms have not been established. Skeletal muscle develops from the fusion of precursor myoblasts into myofibers. We have used the C2C12 skeletal muscle myoblast cell line, primary myoblasts, and mouse models of resistance to thyroid hormone (RTH) α and ß, to determine the role of thyroid hormone in the regulation of myoblast differentiation. T3, which activates thyroid hormone receptor (TR) α and ß, increased myoblast differentiation whereas GC1, a selective TRß agonist, was minimally effective. Genetic approaches confirmed that TRα plays an important role in normal myoblast proliferation and differentiation and acts through the Wnt/ß-catenin signaling pathway. Myoblasts with TRα knockdown, or derived from RTH-TRα PV (a frame-shift mutation) mice, displayed reduced proliferation and myogenic differentiation. Moreover, skeletal muscle from the TRα1PV mutant mouse had impaired in vivo regeneration after injury. RTH-TRß PV mutant mouse model skeletal muscle and derived primary myoblasts did not have altered proliferation, myogenic differentiation, or response to injury when compared with control. In conclusion, TRα plays an essential role in myoblast homeostasis and provides a potential therapeutic target to enhance skeletal muscle regeneration.

A novel perfusion-based method for cochlear implant electrode insertion.

A cochlear implant (CI) restores partial hearing to profoundly deaf individuals. CI electrodes are inserted manually in the cochlea and surgeons rely on tactile feedback from the implant to determine when to stop the insertion. This manual insertion method results in a large degree of variability in surgical outcomes and intra-cochlear trauma. Additionally, implants often span only the basal turn. In the present study we report on the development of a new method to assist CI electrode insertion. The design objectives are (1) an automated and standardized insertion technique across patients with (2) more apical insertion than is possible by the contemporary methods, while (3) minimizing insertion trauma. The method relies on a viscous fluid flow through the cochlea to carry the electrode array with it. A small cochleostomy (∼100-150 um in diameter) is made in scala vestibuli (SV) and the round window (RW) membrane is opened. A flow of diluted Sodium Hyaluronate (also known as Hyaluronic Acid, (HA)) is set up from the RW to the SV opening using a perfusion pump that sets up a unidirectional flow. Once the flow is established an implant is dropped into the ongoing flow. Here we present a proof-of-concept study where we used this technique to insert silicone implants all the way to the cochlear apex in rats and gerbils. In light-microscopic histology, the implantation occurred without cochlear trauma. To further assess the ototoxicity of the HA perfusion, we measured compound action potential (CAP) thresholds following the perfusion of HA, and found that the CAP thresholds were substantially elevated. Thus, at this point the method is promising, and requires further development to become clinically viable.

ß-Cell regeneration mediated by human bone marrow mesenchymal stem cells.

Bone marrow mesenchymal stem cells (BMSCs) have been shown to ameliorate diabetes in animal models. The mechanism, however, remains largely unknown. An unanswered question is whether BMSCs are able to differentiate into ß-cells in vivo, or whether BMSCs are able to mediate recovery and/or regeneration of endogenous ß-cells. Here we examined these questions by testing the ability of hBMSCs genetically modified to transiently express vascular endothelial growth factor (VEGF) or pancreatic-duodenal homeobox 1 (PDX1) to reverse diabetes and whether these cells were differentiated into ß-cells or mediated recovery through alternative mechanisms. Human BMSCs expressing VEGF and PDX1 reversed hyperglycemia in more than half of the diabetic mice and induced overall improved survival and weight maintenance in all mice. Recovery was sustained only in the mice treated with hBMSCs-VEGF. However, de novo ß-cell differentiation from human cells was observed in mice in both cases, treated with either hBMSCs-VEGF or hBMSCs- PDX1, confirmed by detectable level of serum human insulin. Sustained reversion of diabetes mediated by hBMSCs-VEGF was secondary to endogenous ß-cell regeneration and correlated with activation of the insulin/IGF receptor signaling pathway involved in maintaining ß-cell mass and function. Our study demonstrated the possible benefit of hBMSCs for the treatment of insulin-dependent diabetes and gives new insight into the mechanism of ß-cell recovery after injury mediated by hBMSC therapy.

Novel mechanism of the vascular protector prostacyclin: regulating microRNA expression.

Prostacyclin (PGI(2)) is a key vascular protector, metabolized from endogenous arachidonic acid (AA). Its actions are mediated through the PGI(2) receptor (IP) and nuclear receptor, peroxisome proliferator-activated receptor γ (PPARγ). Here, we found that PGI(2) is involved in regulating cellular microRNA (miRNA) expression through its receptors in a mouse adipose tissue-derived primary culture cell line expressing a novel hybrid enzyme gene (COX-1-10aa-PGIS), cyclooxygenase-1 (COX-1) and PGI(2) synthase (PGIS) linked with a 10-amino acid linker. The triple catalytic functions of the hybrid enzyme in these cells successfully redirected the endogenous AA metabolism toward a stable and dominant production of PGI(2). The miRNA microarray analysis of the cell line with upregulated PGI(2) revealed a significant upregulation (711, 148b, and 744) and downregulation of miRNAs of interest, which were reversed by antagonists of the IP and PPARγ receptors. Furthermore, we also found that the insulin-mediated lipid deposition was inhibited in the PGI(2)-upregulated adipocytes. The study also initiated a discussion that suggested that the endogenous PGI(2) inhibition of lipid deposition in adipocytes could involve miRNA-mediated inhibition of expression of the targeted genes. This indicated that PGI(2)-miRNA regulation could exist in broad pathophysiological processes involving PGI(2) (i.e., apoptosis, vascular inflammation, cancer, embryo implantation, and obesity).

Structural and functional analysis of the C-terminus of Galphaq in complex with the human thromboxane A2 receptor provides evidence of constitutive activity.

The human thromboxane A(2) (TXA(2)) receptor (TP) is known to mediate platelet aggregation and vasoconstriction. The receptor predominantly interacts with the Gq protein, thereby activating phospholipase C and increasing the intracellular calcium level. In this study, we synthesized a 15-residue peptide corresponding to the C-terminal domain of the Gq protein alpha subunit (Galphaq-Ct peptide) and characterized its interaction with recombinant TP purified from a baculovirus expression system in the presence and absence of an agonist using fluorescence and NMR spectroscopic studies. With fluorescence binding assays, we demonstrated that the Galphaq-Ct peptide was bound to TP, in the absence of the agonist, with a K(d) value of approximately 17 muM. Interestingly, upon addition of the agonist, U46619, the Galphaq-Ct peptide's binding affinity for this activated TP was reduced, thereby increasing the K(d) value to approximately 240 muM. NMR experiments demonstrated that the TP-bound Galphaq-Ct peptide shows a different affinity and conformation, in the absence and presence of the agonist, U46619. This suggested there is the possibility of ligand-free constitutive TP signaling through Galpha binding. Thus, an HEK293 cell line that stably expresses human TP and lacks the ability to produce TXA(2) was created by gene transfer and G418 selection. In comparison with the control cells, the stable cell line showed significant Galpha-mediated ligand-free calcium signaling. The study indicates a promising new outlook for the examination of prostanoid receptor-G-protein interactions in greater detail using integrated NMR spectroscopy, the purified receptor, and the stable cell line.

Engineering of a novel hybrid enzyme: an anti-inflammatory drug target with triple catalytic activities directly converting arachidonic acid into the inflammatory prostaglandin E2.

Cyclooxygenase isoform-2 (COX-2) and microsomal prostaglandin E(2) synthase-1 (mPGES-1) are inducible enzymes that become up-regulated in inflammation and some cancers. It has been demonstrated that their coupling reaction of converting arachidonic acid (AA) into prostaglandin (PG) E(2) (PGE(2)) is responsible for inflammation and cancers. Understanding their coupling reactions at the molecular and cellular levels is a key step toward uncovering the pathological processes in inflammation. In this paper, we describe a structure-based enzyme engineering which produced a novel hybrid enzyme that mimics the coupling reactions of the inducible COX-2 and mPGES-1 in the native ER membrane. Based on the hypothesized membrane topologies and structures, the C-terminus of COX-2 was linked to the N-terminus of mPGES-1 through a transmembrane linker to form a hybrid enzyme, COX-2-10aa-mPGES-1. The engineered hybrid enzyme expressed in HEK293 cells exhibited strong triple-catalytic functions in the continuous conversion of AA into PGG(2) (catalytic-step 1), PGH(2) (catalytic-step 2) and PGE(2) (catalytic-step 3), a pro-inflammatory mediator. In addition, the hybrid enzyme was also able to directly convert dihomo-gamma-linolenic acid (DGLA) into PGG(1), PGH(1) and then PGE(1) (an anti-inflammatory mediator). The hybrid enzyme retained similar K(d) and V(max) values to that of the parent enzymes, suggesting that the configuration between COX-2 and mPGES-1 (through the transmembrane domain) could mimic the native conformation and membrane topologies of COX-2 and mPGES-1 in the cells. The results indicated that the quick coupling reaction between the native COX-2 and mPGES-1 (in converting AA into PGE(2)) occurred in a way so that both enzymes are localized near each other in a face-to-face orientation, where the COX-2 C-terminus faces the mPGES-1 N-terminus in the ER membrane. The COX-2-10aa-mPGES-1 hybrid enzyme engineering may be a novel approach in creating inflammation cell and animal models, which are particularly valuable targets for the next generation of NSAID screening.

Ligand-specific conformation determines agonist activation and antagonist blockade in purified human thromboxane A2 receptor.

The binding of an agonist to a G protein-coupled receptor (GPCR) causes its coupling to different G proteins, which mediate signaling. However, the binding of an antagonist to the same site of the GPCR could not induce coupling. To understand the molecular mechanism involved, the structural flexibility of the purified human thromboxane A2 receptor (TP) was characterized by spectroscopic approaches, while bound to an agonist or antagonist. Circular dichroism not only revealed that the purified TP adopted more than 50% helical conformation in solution but also showed that the antagonist, SQ29,548, could induce more of a beta-sheet structure in the TP than that of the agonist, U46619. Also, fluorescence studies showed that the antagonist induced the intrinsic Trp fluorescence signal change more than the agonist. Furthermore, three of the nine tryptophan residues involved in the different ligand-based structural changes were demonstrated by NMR spectroscopy. Low pH-induced changes in the receptor conformation and molecular interaction field dramatically increased the agonist binding but did not significantly affect the antagonist binding. Different conformational changes were also observed in the TP reconstituted into phosphatidylcholine/phosphatidylserine/phosphatydylethanolamine-formed liposomes. These studies are the first to show a possible mechanism of the ligand-specific conformation-dependent agonist activation and antagonist blockage in the GPCR.

An active triple-catalytic hybrid enzyme engineered by linking cyclo-oxygenase isoform-1 to prostacyclin synthase that can constantly biosynthesize prostacyclin, the vascular protector.

It remains a challenge to achieve the stable and long-term expression (in human cell lines) of a previously engineered hybrid enzyme [triple-catalytic (Trip-cat) enzyme-2; Ruan KH, Deng H & So SP (2006) Biochemistry45, 14003-14011], which links cyclo-oxygenase isoform-2 (COX-2) to prostacyclin (PGI(2)) synthase (PGIS) for the direct conversion of arachidonic acid into PGI(2) through the enzyme's Trip-cat functions. The stable upregulation of the biosynthesis of the vascular protector, PGI(2), in cells is an ideal model for the prevention and treatment of thromboxane A(2) (TXA(2))-mediated thrombosis and vasoconstriction, both of which cause stroke, myocardial infarction, and hypertension. Here, we report another case of engineering of the Trip-cat enzyme, in which human cyclo-oxygenase isoform-1, which has a different C-terminal sequence from COX-2, was linked to PGI(2) synthase and called Trip-cat enzyme-1. Transient expression of recombinant Trip-cat enzyme-1 in HEK293 cells led to 3-5-fold higher expression capacity and better PGI(2)-synthesizing activity as compared to that of the previously engineered Trip-cat enzyme-2. Furthermore, an HEK293 cell line that can stably express the active new Trip-cat enzyme-1 and constantly synthesize the bioactive PGI(2) was established by a screening approach. In addition, the stable HEK293 cell line, with constant production of PGI(2), revealed strong antiplatelet aggregation properties through its unique dual functions (increasing PGI(2) production while decreasing TXA(2) production) in TXA(2) synthase-rich plasma. This study has optimized engineering of the active Trip-cat enzyme, allowing it to become the first to stably upregulate PGI(2) biosynthesis in a human cell line, which provides a basis for developing a PGI(2)-producing therapeutic cell line for use against vascular diseases.

Large-scale expression, purification, and characterization of an engineered prostacyclin-synthesizing enzyme with therapeutic potential.

Recently, we reported that a novel hybrid enzyme (TriCat enzyme), engineered by linking human cyclooxygenase-2 (COX-2) with prostacyclin (PGI(2)) synthase (PGIS) together through a transmembrane domain, was able to directly integrate the triple catalytic (TripCat) functions of COX-2 and PGIS and effectively convert arachidonic acid (AA) into the vascular protector, PGI(2) [K.H. Ruan, H. Deng, S.P. So, Biochemistry 45 (2006) 14003-14011]. In order to confirm the important biological activity and evaluate its therapeutic potential, it is critical to characterize the properties of the enzyme using the purified protein. The TriCat enzyme cDNA was subcloned into a baculovirus vector and its protein was expressed in Sf-9 cells in large-scale with a high-yield ( approximately 4% of the total membrane protein), as confirmed by Western blot and protein staining. The Sf-9 cells' membrane fraction, rich in TriCat enzyme, exhibited strong TriCat functions (K(m)=3 microM and K(cat)=100 molecules/min) for the TriCat enzyme and was 3-folds faster in converting AA to PGI(2) than the combination of the individual COX-2 and PGIS. Another superiority of the TriCat enzyme is its dual effect on platelet aggregation: it completely inhibited platelet aggregation at the low concentration of 2 microg/ml and then displayed the ability to reverse the initially aggregated platelets to their non-aggregated state. Furthermore, multiple substrate-binding sites were confirmed in the single protein by high-resolution NMR spectroscopy, using partially purified TriCat enzyme. These studies have clearly demonstrated that the isolated TriCat enzyme protein functions in the selective biosynthesis of the vascular protector, PGI(2), and revealed its potential for anti-thrombosis therapeutics.

Characterization of the prostaglandin H2 mimic: binding to the purified human thromboxane A2 receptor in solution.

For decades, the binding of prostaglandin H(2) (PGH(2)) to multiple target proteins of unrelated protein structures which mediate diverse biological functions has remained a real mystery in the field of eicosanoid biology. Here, we report that the structure of a PGH(2) mimic, U46619, bound to the purified human TP, was determined and compared with that of its conformation bound to the COX-downstream synthases, prostacyclin synthase (PGIS) and thromboxane A(2) synthase (TXAS). Active human TP protein, glycosylated and in full length, was expressed in Sf-9 cells using a baculovirus (BV) expression system and then purified to near homogeneity. The binding of U46619 to the purified receptor in a nonionic detergent-mimicked lipid environment was characterized by high-resolution NMR spectroscopy. The conformational change of U46619, upon binding to the active TP, was evidenced by the significant perturbation of the chemical shifts of its protons at H3 and H4 in a concentration-dependent manner. The detailed conformational changes and 3D structure of U46619 from the free form to the TP-bound form were further solved by 2D (1)H NMR experiments using a transferred NOE (trNOE) technique. The distances between the protons of H11 and H18, H11 and H19, H15 and H18, and H15 and H19 in U46619 were shorter following their binding to the TP in solution, down to within 5A, which were different than that of the U46619 bound to PGIS and U44069 (another PGH(2) mimic) bound to TXAS. These shorter distances led to further separation of the U46619 alpha and omega chains, forming a unique "rectangular" shape. This enabled the molecule to fit into the ligand-binding site pocket of a TP model, in which homology modeling was used for the transmembrane (TM) domain, and NMR structures were used for the extramembrane loops. The proton perturbations and 3D conformations in the TP-bound U46619 were different with that of the PGH(2) mimics bound to PGIS and TXAS. The studies indicated that PGH(2) can adopt multiple conformations in solution to satisfy the specific and unique shapes to fit the different binding pockets in the TP receptor and COX-downstream enzymes. The results also provided sufficient information for speculating the molecular basis of how PGH(2) binds to multiple target proteins even though unrelated in their protein sequences.

A simple, quick, and high-yield preparation of the human thromboxane A2 receptor in full size for structural studies.

Human thromboxane A2 receptor (TP), a G protein-coupled receptor (GPCR), is one of the most promising targets for developing the next generation of anti-thrombosis and hypertension drugs. However, obtaining a sufficient amount of the full-sized and active membrane protein has been the major obstacle for structural elucidation that reveals the molecular mechanisms of the receptor activation and drug designs. Here we report an approach for the simple, quick, and high-yield preparation of the purified and active full-sized TP in an amount suitable for structural studies. Glycosylated human TP was highly expressed in Sf-9 cells using an optimized baculovirus (BV) expression system. The active receptor was extracted and solubilized by different detergents for comparison and was finally purified to a nearly single band with a ratio of 1:0.9 +/- 0.05 (ligand:receptor molecule) in ligand binding using a Ni column with a relatively low yield. However, a high-yield purification (milligram quantity) of the TP protein, from a modulate scale of transfected Sf-9 cell culture, has been achieved by quick and simple purification steps, which include DNA digestion, dodecyl-maltoside detergent extraction, centrifugation, and FPLC purification. The purity and quantity of the purified TP, using the high-yield approach, were suitable for protein structural studies as evidenced by SDS-PAGE, Western blot analyses, ligand binding assays, and a feasibility test using high-resolution one-dimensional and two-dimensional (1)H NMR spectroscopic analyses. These studies provide a basis for the high-yield expression and purification of the GPCR for the structural and functional characterization using biophysics approaches.

Characterization of the substrate mimic bound to engineered prostacyclin synthase in solution using high-resolution NMR spectroscopy and mutagenesis: implication of the molecular mechanism in biosynthesis of prostacyclin.

High-resolution NMR spectroscopy was used to determine the docking of a substrate (prostaglandin H2) mimic (U46619) to the engineered prostacyclin (PGI2) synthase (PGIS) in solution. The binding of U46619 to the PGIS protein was demonstrated by 1D NMR titration, and the significant perturbation of the chemical shifts of protons at C-11, H2C, and H20 of U46619 were observed upon U46619 binding to the engineered PGIS in a concentration-dependent manner. The detailed conformational change and 3D structure of the PGIS-bound U46619 were further demonstrated by 2D 1H NMR experiments using the transferred NOE technique. The distances between the protons H20 and H2, H18 and H2, and H18 and H4 are shorter following their binding to the PGIS in solution-down to within 5 A. These shorter distances resulted in a widely open conformation, where the triangle shape of the unbound U46619 changed to a more compact conformation with an oval shape. The bound conformation of U46619 fits the crystal structure of the PGIS substrate binding pocket considerably better than that of the unbound U46619. The residues important to the substrate binding in the active site pocket of PGIS were also predicted. For example, Trp282 could be one of the most important residues and is suspected to play a role in the determination of specific catalytic function, which has been established by the docking studies using the NMR structure of the PGIS-bound form of U46619 and the PGIS crystal structure. These studies have provided the structural information for the interaction of the PGIS with its substrate mimic. The noted conformational changes where the C-6 position is closer to the C-9 position of U46619 provided the first experimental data for understanding the molecular mechanism of the catalytic function of PGIS in the isomerization of PGH2 to prostacyclin.

A profile of the residues in the second extracellular loop that are critical for ligand recognition of human prostacyclin receptor.

The residues in the second extracellular loop (eLP2) of the prostanoid receptors, which are important for specific ligand recognition, were previously predicted in our earlier studies of the thromboxane A2 receptor (TP) using a combination of NMR spectroscopy and recombinant protein approaches. To further test this hypothesis, another prostanoid receptor, the prostacyclin receptor (IP), which has opposite biological characteristics to that of TP, was used as a model for these studies. A set of recombinant human IPs with site-directed mutations at the nonconserved eLP2 residues were constructed using an Ala-scanning approach, and then expressed in HEK293 and COS-7 cells. The expression levels of the recombinant receptors were six-fold higher in HEK293 cells than in COS-7 cells. The residues important for ligand recognition and binding within the N-terminal segment (G159, Q162, and C165) and the C-terminal segment (L172, R173, M174, and P179) of IP eLP2 were identified by mutagenesis analyses. The molecular mechanisms for the specific ligand recognition of IP were further demonstrated by specific site-directed mutagenesis using different amino acid residues with unique chemical properties for the key residues Q162, L172, R173, and M174. A comparison with the corresponding functional residues identified in TP eLP2 revealed that three (Q162, R173, and M174) of the four residues are nonconserved, and these are proposed to be involved in specific ligand recognition. We discuss the importance of G159 and P179 in ligand recognition through configuration of the loop conformation is discussed. These studies have further indicated that characterization of the residues in the eLP2 regions for all eight prostanoid receptors could be an effective approach for uncovering the molecular mechanisms of the ligand selectivities of the G-protein-coupled receptors.