Dibazol-induced relaxation of ophthalmic artery in C57BL/6J mice is correlated with the potency to inhibit voltage-gated Ca2+ channels.

We aimed to explore the effect of dibazol on the ophthalmic artery (OA) and ophthalmic artery smooth muscle cells (OASMCs) of C57BL/6J mice as well as the underlying mechanisms. The OA of C57BL/6J mice was isolated under a dissecting microscope for primary OASMCs culture and myogenic tests. OASMCs were identified through morphological and immunofluorescence analyses. Morphology changes in the OASMCs were examined by staining using rhodamine-phalloidin. We performed a collagen gel contraction assay to measure the contractile and relaxant activities of the OASMCs. The molecular probe Fluo-4 AM was used to examine intracellular free Ca2+ levels ([Ca2+]in). The myogenic effects of OA were examined using wire myography. Additionally, the whole-cell patch-clamp technique was used to investigate the mechanisms underlying the relaxant effect of dibazol on L-type voltage-gated Ca2+ channels (LVGC) in isolated cells. 10-5 M dibazol significantly inhibited the contraction of OASMCs and increased the [Ca2+]in response to 30 mM KCl in a concentration-dependent manner. Dizabol had a more significant relaxant effect than 10-5 M isosorbide dinitrate (ISDN). Similarly, dibazol showed a significant dose-dependent relaxant effect on OA contraction induced by 60 mM KCl or 0.3 µM 9,11-Dideoxy-9α,11α-methanoepoxy prostaglandin F2α (U46619). The current-voltage (I-V) curve revealed that dibazol decreased Ca2+ currents in a concentration-dependent manner. In conclusion, dibazol exerted relaxant effects on the OA and OASMCs, which may involve the inhibition of the Ca2+ influx through LVGC in the cells.

Connexins may play a critical role in cigarette smoke-induced pulmonary hypertension.

Pulmonary hypertension (PH) is a chronic progressive disease characterized by pulmonary vasoconstriction and remodeling. It causes a gradual increase in pulmonary vascular resistance leading to right-sided heart failure, and may be fatal. Chronic exposure to cigarette smoke (CS) is an essential risk factor for PH group 3; however, smoking continues to be prevalent and smoking cessation is reported to be difficult. A majority of smokers exhibit PH, which leads to a concomitant increase in the risk of mortality. The current treatments for PH group 3 focus on vasodilation and long-term oxygen supplementation, and fail to stop or reverse PH-associated continuous vascular remodeling. Recent studies have suggested that pulmonary vascular endothelial dysfunction induced by CS exposure may be an initial event in the natural history of PH, which in turn may be associated with abnormal alterations in connexin (Cx) expression. The relationship between Cx and CS-induced PH development has not yet been directly investigated. Therefore, this review will describe the roles of CS and Cx in the development of PH and discuss the related downstream pathways. We also discuss the possible role of Cx in CS-induced PH. It is hoped that this review may provide new perspectives for early intervention.

The pharmacological properties and corresponding mechanisms of farrerol: a comprehensive review.

CONTEXT: Farrerol, a typical natural flavanone isolated from the traditional Chinese herb 'Man-shan-hong' [Rhododendron dauricum L. (Ericaceae)] with phlegm-reducing and cough-relieving properties, is widely used in China for treating bronchitis and asthma. OBJECTIVE: To present the anti-inflammatory, antioxidant, vasoactive, antitumor, and antimicrobial effects of farrerol and its underlying molecular mechanisms. METHODS: The literature was reviewed by searching PubMed, Medline, Web of Knowledge, Scopus, and Google Scholar databases between 2011 and May 2021. The following key words were used: 'farrerol,' 'flavanone,' 'anti-inflammatory,' 'antioxidant,' 'vasoactive,' 'antitumor,' 'antimicrobial,' and 'molecular mechanisms'. RESULTS: Farrerol showed anti-inflammatory effects mainly mediated via the inhibition of interleukin (IL)-6/8, IL-1ß, tumour necrosis factor(TNF)-α, NF-κB, NO, COX-2, JNK1/2, AKT, PI3K, ERK1/2, p38, Keap-1, and TGF-1ß. Farrerol exhibited antioxidant effects by decreasing JNK, MDA, ROS, NOX4, Bax/Bcl-2, caspase-3, p-p38 MAPK, and GSK-3ß levels and enhancing Nrf2, GSH, SOD, GSH-Px, HO-1, NQO1, and p-ERK levels. The vasoactive effects of farrerol were also shown by the reduced α-SMA, NAD(P)H, p-ERK, p-Akt, mTOR, Jak2, Stat3, Bcl-2, and p38 levels, but increased OPN, occludin, ZO-1, eNOS, CaM, IP3R, and PLC levels. The antitumor effects of farrerol were evident from the reduced Bcl-2, Slug, Zeb-1, and vimentin levels but increased p27, ERK1/2, p38, caspase-9, Bax, and E-cadherin levels. Farrerol reduced α-toxin levels and increased NO production and NF-κB activity to impart antibacterial activity. CONCLUSIONS: This review article provides a theoretical basis for further studies on farrerol, with a view to develop and utilise farrerol for treating of vascular-related diseases in the future.

Arabidopsis REM16 acts as a B3 domain transcription factor to promote flowering time via directly binding to the promoters of SOC1 and FT.

Actin depolymerizing factor (ADF) is a key modulator for dynamic organization of actin cytoskeleton. Interestingly, it was found that the ADF1 gene silencing delays flowering, but its mechanism remains unclear. In this study, ADF1 was used as a bait to screen its interacting proteins by the yeast two-hybrid (Y2H) system. One of them, the REM16 transcription factor was identified. As one of the AP2/B3-like transcriptional factor family members, the REM16 contains two B3 domains and its transcript levels kept increasing during the floral transition stage. Overexpression of REM16 accelerates flowering while silencing of REM16 delays flowering. Gene expression analysis indicated that the key flowering activation genes such as CONSTANS (CO), FLOWERING LOCUS T (FT), LEAFY (LFY) and SUPPRESSOR OF OVEREXPRESSION OF CONSTANS (SOC1) were upregulated in the REM16 overexpression lines, while the transcription of the flowering suppression gene FLOWERING LOCUS C (FLC) was decreased. In contrast, the REM16 gene silencing lines contained lower transcript levels of the CO, FT, LFY and SOC1 but higher transcript levels of the FLC compared with the wild-type plants. It was proved that REM16 could directly bind to the promoter regions of SOC1 and FT by in vitro and in vivo assays. Genetic analysis supported that REM16 acts upstream of SOC1 and FT in flowering pathways. All these studies provided strong evidence demonstrating that REM16 promotes flowering by directly activating SOC1 and FT.

Speciation of Ionic Uranyl-Containing Complexes in in Situ Formed Dicyanonitrosomethanide-Based Ionic Liquids.

A series of ionic uranyl-containing complexes, namely [C2mim]2[UO2(ccnm)4] (1), [C4mim]2[UO2(ccnm)4] (2), [N1111]2[UO2(ccnm)4][H2O]2 (3), and [P2444]2[UO2(dcnm)2(ccnm)2] (4) [(ccnm)- = carbamoylcyanonitrosomethanide; dcnm = dicyanonitrosomethanide; (C2mim)+ = 1-ethyl-3-methylimidazolium; (C4mim)+ = 1-butyl-3-methylimidazolium; (N1111)+ = tetramethylammonium; (P2444)+ = tributyl(ethyl)phosphonium)], were isolated from in situ formed dcnm-based ionic liquids and characterized systematically. It was found that the dcnm anions transformed into ccnm anions during the reactions. These anions coordinate with the uranyl cations in chelate or terminal monodentate coordination mode, affording negative divalent complex anions which can combine with different organic cations and form ionic uranyl-containing complexes. Plenty of C-H···O, N-H···O, C-H···N, N-H···N, and H···H weak interactions are formed in the crystal structures. The transformation of cyano to amide groups contributes to the crystallinity and leads to higher melting points as well as the luminescence quenching of these compounds.

Rhomboid intercostal block combined with sub-serratus plane block versus rhomboid intercostal block for postoperative analgesia after video-assisted thoracoscopic surgery: a prospective randomized-controlled trial.

BACKGROUND: Rhomboid intercostal block (RIB) and Rhomboid intercostal block with sub-serratus plane block (RISS) are the two types of plane blocks used for postoperative analgesia after video-assisted thoracoscopic surgery (VATS). This prospective randomized controlled trial was performed to analyze the postoperative analgesic effects of ultrasound-guided RIB block and RISS block after video-assisted thoracoscopic surgery. METHODS: Ninety patients aged between 18 and 80 years, with American Society of Anesthesiologists physical status Classes I-II and scheduled for elective unilateral VATS were randomly allocated into three groups. In group C, no block intervention was performed. Patients in group RIB received ultrasound-guided RIB with 20-mL 0.375% ropivacaine and those in group RISS received ultrasound-guided RIB and serratus plane block using a total of 40-mL 0.375% ropivacaine. All patients received intravenous sufentanil patient-controlled analgesia upon arrival in the recovery room. Postoperative sufentanil consumption and pain scores were compared among the groups. RESULTS: The dosages of sufentanil consumption at 24 h after the surgery in the RIB and RISS groups were significantly lower than that in group C (p < 0.001 and p < 0.001 for all comparisons, respectively), the postoperative Numerical Rating Scale (NRS) scores in the RIB and RISS groups at 0.5, 1, 3, 6, 12, 18, and 24 h after surgery when patients were at rest or active were significantly lower than that in group C (p < 0.05 for all comparisons). The required dosage of sufentanil and time to first postoperative analgesic request in groupRISS were less than those in the group RIB at 24 h after the surgery (p < 0.001 and p < 0.001 for all comparisons, respectively). Similarly, the Numerical Rating Scale scores for group RISS at 12, 18, and 24 h after the surgery when the patients were active were significantly lower than those for group RIB (p < 0.05 for all comparisons). CONCLUSION: Both ultrasound-guided RIB block and RISS block can effectively reduce the demand for sufentanil within 24 h after VATS, and less sufentanil dosage is needed in patient with RISS block. Ultrasound-guided RIB block and RISS block can effectively relieve pain within 24 h after VATS, and RISS block is more effective.

Probing the toxic interactions between bisphenol A and glutathione S-transferase Phi8 from Arabidopsis thaliana.

As primary polymer material in industrial products, bisphenol A (BPA) has become one of the most productive chemicals. Excluding its endocrine-disrupting property, BPA can also produce excessive reactive oxygen species (ROS). Nevertheless, the underlying toxic mechanisms of BPA-induced oxidative damages to plants are still unknown. In this work, glutathione S-transferase Phi8 was used as biomarker to evaluate the hazardous oxidative effects of BPA at the molecular level. Firstly, the intrinsic fluorescence of AtGSTF8 was statically quenched along with complex formation and structural and conformational changes, which led to the loosening and unfolding of the framework of AtGSTF8 as well as the increase of hydrophilicity around Trp residues. Then a single binding site was predicted for AtGSTF8 towards BPA and the complex formation was predominantly driven by hydrophobic interactions owing to the positive ΔH and ΔS. Besides, the predicted binding site of BPA was close to the H-site of AtGSTF8 which was surrounded by several hydrophobic amino acids based on the molecular docking results. The activity of glutathione S-transferase was declined and the plant growth was destroyed upon complex formation. The investigation of the binding mechanism of BPA with AtGSTF8 at molecular level would provide experimental assessments on toxicological effects of BPA on plants.

Variability of Uranyl Carboxylates from Rigid Terophenyldicarboxylic Acid Ligands.

Three uranyl carboxylates, namely, (UO2)(L1)(H2O)0.5 (1), [(UO2)(L2)(H2O)]·2H2O (2), and [(UO2)(L2)(H2O)]·(CH3CN) (3), were synthesized hydrothermally from 2',3',5',6'-tetramethyl-(1,1':4',1″-terphenyl)-4,4″-dicarboxylic acid (H2L1) and 2',5'-dimethyl-(1,1':4',1″-terphenyl)-3,3″-dicarboxylic acid (H2L2), which are all steric carboxylic acid ligands but vary with the carboxylic acid group position and methyl group number. It is found that compound 1 displays a three-dimensional 8-fold-interpenetrated net with channels running along the c direction. Compounds 2 and 3 are isostructural, and all display two-dimensional-layered crystal structures but contain different guest molecules. The photophysical measurements reveal that compounds 1 and 2, which contain disordered water molecules, are luminescence-quenched, whereas compound 3 containing acetonitrile molecules is luminescent.

Synthesis of Anhydrous Acetates for the Components of Nuclear Fuel Recycling in Dialkylimidazolium Acetate Ionic Liquids.

A series of anhydrous acetate salts with uranium {[C2C1im][UO2(OAc)3] (1), [C2C2im][UO2(OAc)3] (2), and [C4C1im][UO2(OAc)3] (3)}, lanthanides {[C2C2im]2[La(OAc)5] (4) and [C2C1im]2[Nd(OAc)5] (5)}, and strontium {[C2C1im]n[Sr(OAc)3]n (6)} (where C2C1im = 1-ethyl-3-methylimidazolium, C2C2im = 1,3-diethylimidazolium, C4C1im = 1-butyl-3-methylimidazolium, and OAc = acetate) have been prepared and structurally characterized. Both lanthanides and strontium are common components of the nuclear fuel waste, and their separation from uranium is an important but still challenging task. A new synthetic approach with dialkylimidazolium acetate ionic liquids (ILs) as the solvent has been developed for the direct synthesis of homoleptic acetates from the corresponding hydrates and, unexpectedly, hardly soluble f-element oxides. Although the group of characterized compounds shows perfect structural variability, all actinide and lanthanide metal ions form monomeric complex anions where the metal cation coordinates to five ligands including two oxygen atoms in the case of uranium, as is commonly observed for uranyl compounds. Crystallographic analyses revealed that the complex [UO2(OAc)3]- anions possess rather standard D3h symmetry featuring a hexagonal-bipyramidal coordination environment, while the lanthanide anions [Ln(OAc)5]2- are fully asymmetric and the Ln3+ cations are 10-coordinated in the form of a distorted bicapped tetragonal antiprism. This is the first report of lanthanide ions coordinated in this fashion. For Sr2+, 9-fold coordination through oxygen atoms in the form of a strongly distorted tricapped trigonal prism is observed. The crystallization of anhydrous, homoleptic, anionic acetate complexes from such a large variety of different metal salts appears to be due to the properties of dialkylimidazolium acetate ILs themselves, including enhanced basicity from the high concentration of free anions and their greater affinity for hydrogen-bonding solutes relative to metal cations.

Structural Tuning and Sensitization of Uranyl Phosphonates by Incorporation of Countercations into the Framework.

By the introduction of terephthalic acid, tetramethylammonium chloride, and Zn2+ ions, three new uranyl triphosphonates with varying crystal structures, namely, [H3O][(UO2)2(HL)]·H2O (1), [NMe4][(UO2)2(HL)(H2O)]·H2O (2), and [(UO2)3Zn(H2L)2(H2O)2]·3H2O (3), where H6L = benzene-1,3,5-triyltris(methylene) triphosphonic acid, have been successfully synthesized and characterized by means of powder and single crystal XRD, IR, EA, TGA, UV-vis, and luminescence. These three compounds all possess three-dimensional framework structures with hydrium, tetramethylammonium, and Zn2+ as the respective countercations. The uranium(VI) center luminescence of compounds 1 and 2 is completely quenched. However, the incorporation of Zn2+ into the matrix of uranyl phosphonate in the case of compound 3 results in the emerging of the typical intense vibronic emissions of U(VI), demonstrating that zinc phosphonate can behave as sensitizer of uranyl phosphonates. The quenching and sensitization mechanism were also discussed.

Farrerol Modulates Aorta Gene Expression Profile in Spontaneously Hypertensive Rats.

Farrerol, a typical natural flavanone and major active component in Rhododendron dauricum var. ciliatum, has been shown to possess vasoactive ability in vitro. The aim of this study was to investigate its effect on aorta gene expression in spontaneously hypertensive rats. Twelve-week-old male normotensive Wistar Kyoto rats and spontaneously hypertensive rats were treated with orally administered farrerol (50 mg/kg body weight) for 8 wk before they were sacrificed. We found that aorta samples showed 444 upregulated genes in control spontaneously hypertensive rats compared with the control Wistar Kyoto rats. Administration of farrerol in spontaneously hypertensive rats increased the expression of 2329 genes in the aorta compared with the control spontaneously hypertensive rats. Gene expression profiles performed on the aorta revealed that farrerol induced changes in vascular smooth muscle contraction, mitogen-activated protein kinase signaling pathway, regulation of actin cytoskeleton, vascular endothelial growth factor signaling pathway, calcium signaling pathway, and renin angiotensin system. Furthermore, 10 genes involved in the pathway of vascular smooth muscle contraction were verified using real-time polymerase chain reaction technique, and several novel potential target genes for the farrerol treatment of hypertension were identified. The findings of this study lend support to the potential use of farrerol as a novel therapeutic and antihypertensive candidate drug to prevent the development of hypertension.

Expression, purification and characterization of ROP66-178 GTPase from Arabidopsis thaliana.

The unique type of GTPases in plants, termed ROPs, are the small GTP-binding proteins involved in signal transduction which play important roles in regulation of hormonal response pathway, cell polarity, defense from plant pathogens, etc. In order to explore the regulation mechanism of AtROPs involved in, the purified ROPs were needed to explore the interactions of ROP GTPases with their regulators and effectors. In this study, the first ROP GTPase from Arabidopsis thaliana, AtROP66-178 was successfully expressed in Escherichia coli and obtained in high quality and purity through affinity chromatography and gel-filtration chromatography. The resultant protein was identified as a single band of 19 kDa in SDS-PAGE and was confirmed to be active to interact with guanine nucleotides through the fluorescence-based assay. The intrinsic tryptophan fluorescence intensity of AtROP66-178 was enhanced upon interacting with either GDP or GTP. Meanwhile, the equilibrium dissociation constants of AtROP66-178 with fluorescent guanine nucleotide analogue mantGDP and mantGTP were determined to be 0.0721 µM and 0.0422 µM, respectively, based on fluorescence polarization.

Fabrication of New Uranyl Phosphonates by Varying Quaternary Ammonium Cation: Synthesis, Structure, Luminescent Properties, and Single-Crystal to Single-Crystal Transformation.

Four new uranyl triphosphonates, namely, [N(CH4)4][UO2(H3L)][H2O] (1), [(UO2)1.5(H3L)(H2O)1.5][H2O] (2), [NBu4][(UO2)3.5(H2L)2][(H2O)4.5] (3), and [(UO2)1.5(H3L)(H2O)2.5][(H2O)2.5] (4), where H6L = benzene-1,3,5-triyltris(methylene)triphosphonic acid, were obtained from a triphosphonate ligand in the presence of different quaternary ammonium cations. The structural characterization revealed that the introduction of quaternary ammonium cation had a major impact on the structure formation of uranyl phosphonates. Compound 1 possesses a three-dimensional anionic framework structure. Tetramethylammonium cations are accommodated in the channels, serving as counterions and structure directing agents. Compound 2 also displays a three-dimensional framework structure but is neutral, because the tetrapropylammonium cations are not involved in the crystal structure. Compound 3 has an intercalation structure; between the layers are the tetrabutylammonium cations, balancing the charge and strengthening the supramolecular structure with C-H···O interactions. No obvious uptake of N2 and CO2 could be observed for compound 2 due to the shrinkage of the framework and structural transformation. Compound 2 undergoes single-crystal to single-crystal transformation under vacuum, leading to the formation of compound 4, which possesses a two-dimensional layer structure. The photophysical properties of these compounds were also investigated.

[Vasodilation of quercetin on rat renal artery and the relationship with L-type voltage-gated Ca2+ channels and protein kinase C].

To investigate the diastolic function of quercetin on rat renal artery in vitro and its mechanism, the tension of rat renal artery was recorded by multi myograph system, and the L-type voltage-gated Ca2+ channels (LVGC) current was recorded by whole-cell patch clamp technique. Quercetin produced relaxation effect on rat renal artery pre-contracted by 60 mmol/L KCl or 1 × 10-5 mol/L phenylephrine, and the maximal diastolic percentage was  (84.53 ± 7.35)% or (76.42 ± 4.63)%. There was no statistical difference in the maximal diastolic percentage between endothelium-intact and endothelium-denuded groups. Pre-incubation of protein kinase C (PKC) inhibitor C6303 inhibited the maximal diastolic amplitude induced by quercetin. The peak current density of LVGC in rat renal artery vascular smooth muscle cells (VSMCs) was (23.17 ± 1.33) pA/pF. Quercetin (10 µmol/L) inhibited the peak current to (10.46 ± 1.35) pA/pF, and the inhibition percentage was 54.86%. C6303 (1 µmol/L) partially reversed the inhibitory effect of quercetin, and the inhibition percentage was 62.08% (P < 0.05). These results suggest that quercetin can relax rat renal artery in vitro in a concentration-dependent and endothelium-independent manner. The vasodilation of quercetin may be related to inhibition of LVGC current and activation of PKC.

[Mechanisms underlying rat coronary arterial vasoconstriction induced by blockade of inward rectifier potassium channels with BaCl2].

In order to explore the mechanisms underlying the vasoconstriction induced by blockade of inward rectifier K+ channels (Kir) with BaCl2, myogenic tone of isolated rat coronary artery (RCA) was recorded with wire myograph. The dependence of BaCl2- induced contraction on intracellular Ca2+ ([Ca2+]i) release and extracellular Ca2+ ([Ca2+]o) influx was studied by Ca2+ deprivation and restoration. The mechanisms underlying BaCl2-induced RCA contraction were investigated with specific inhibitors. BaCl2 (0.1-1.0 mmol/L) contracted isolated RCA in a concentration-dependent manner and the maximal contraction was (5.69 ± 1.07) mN, nearly equal to contraction induced by 60 mmol/L KCl. The contractions induced by BaCl2 in Ca2+-free solution and by followed restoration of 2.5 mmol/L Ca2+ accounted for (35.44 ± 6.72)% and (64.56 ± 5.94)%, respectively. Calcium channel blocker nifedipine (0.3 µmol/L), cyclooxygenase inhibitor indomethacin (100 µmol/L), ERK1/2 inhibitor PD98059 (10 µmol/L) and chloride channel blocker niflumic acid (100 µmol/L) pretreatment depressed the BaCl2-induced maximal contraction by (87.82 ± 5.43)% (P < 0.01), (73.23 ± 5.47)% (P < 0.01), (75.69 ± 7.94)% (P < 0.01) and (83.24 ± 7.69)% (P < 0.01), respectively. These results demonstrate that BaCl2 induces vasoconstriction in RCA by enhancing both [Ca2+]i release and [Ca2+]o influx, and suggest that increase of prostanoids synthesis, activation of calcium channels and chloride channels, as well as ERK1/2 pathway may be involved in this process.

Expression, purification and guanine nucleotide binding characterization of Arabidopsis RabE1d13-185 GTPase.

Arabidopsis RabE1d subclass plays important plant-specific functions in plant growth and development, response to ethylene and defence to plant pathogen, besides their basic cellular role in membrane trafficking. In this study, we present the expression, purification, and characterization of the recombinant core domain of AtRabE1d13-185. AtRabE1d13-185 was successfully expressed in Escherichia coli and purified via two-step nickel affinity chromatography followed by gel filtration, and identified single band in SDS-PAGE. The resultant protein was functionally active, as determined by interaction with guanine nucleotide by a fluorescence-based assay. The intrinsic tryptophan of AtRabE1d13-185 showed fluorescence resonance energy transfer (FRET) effect upon forming complex with fluorescent methylanthraniloyl (mant)-GDP, but quenched when binding with non-labelled guanine nucleotide. The association rate of mantGDP with AtRabE1d13-185 was determined to be 3.48 × 10(7) s(-1) M(-1). The dissociation rates of GDP and mantGDP from the complex with AtRabE1d13-185 were similar. The koff values were determined to be 4.02 × 10(-4) s(-1) based on the FRET effect for the AtRabE1d13-185:GDP and 5.41 × 10(-4) s(-1) for mantGDP excited directly.

A structural basis for Lowe syndrome caused by mutations in the Rab-binding domain of OCRL1.

The oculocerebrorenal syndrome of Lowe (OCRL), also called Lowe syndrome, is characterized by defects of the nervous system, the eye and the kidney. Lowe syndrome is a monogenetic X-linked disease caused by mutations of the inositol-5-phosphatase OCRL1. OCRL1 is a membrane-bound protein recruited to membranes via interaction with a variety of Rab proteins. The structural and kinetic basis of OCRL1 for the recognition of several Rab proteins is unknown. In this study, we report the crystal structure of the Rab-binding domain (RBD) of OCRL1 in complex with Rab8a and the kinetic binding analysis of OCRL1 with several Rab GTPases (Rab1b, Rab5a, Rab6a and Rab8a). In contrast to other effectors that bind their respective Rab predominantly via α-helical structure elements, the Rab-binding interface of OCRL1 consists mainly of the IgG-like ß-strand structure of the ASPM-SPD-2-Hydin domain as well as one α-helix. Our results give a deeper structural understanding of disease-causing mutations of OCRL1 affecting Rab binding.

Structural and functional analysis of the ß-barrel domain of BamA from Escherichia coli.

In gram-negative bacteria, the assembly of outer membrane proteins (OMPs) requires a ß-barrel assembly machinery (BAM) complex, of which BamA is an essential and evolutionarily conserved component. To elucidate the mechanism of BamA-mediated OMP biogenesis, we determined the crystal structure of the C-terminal transmembrane domain of BamA from Escherichia coli (EcBamA) at 2.6 Å resolution. The structure reveals 2 distinct features. First, a portion of the extracellular side of the ß barrel is composed of 5 markedly short ß strands, and the loops stemming from these ß strands form a potential surface cavity, filled by a portion of the L6 loop that includes the conserved VRGF/Y motif found in the Omp85 family. Second, the 4 extracellular loops L3, L4, L6, and L7 of EcBamA form a dome over the barrel, stabilized by a salt-bridge interaction network. Functional data show that hydrophilic-to-hydrophobic mutations of the potential hydrophilic surface cavity and a single Arg547Ala point mutation that may destabilize the dome severely affect the function of EcBamA. Our structure of the EcBamA ß barrel and structure-based mutagenesis studies suggest that the transmembrane ß strands of OMP substrates may integrate into the outer membrane at the interface of the first and last ß strands of the EcBamA barrel, whereas the soluble loops or domains may be transported out of the cell via the hydrophilic surface cavity on dislocation of the VRGF/Y motif of L6. In addition, the dome over the barrel may play an important role in maintaining the efficiency of OMP biogenesis.

Intermediates in the guanine nucleotide exchange reaction of Rab8 protein catalyzed by guanine nucleotide exchange factors Rabin8 and GRAB.

Small G-proteins of the Ras superfamily control the temporal and spatial coordination of intracellular signaling networks by acting as molecular on/off switches. Guanine nucleotide exchange factors (GEFs) regulate the activation of these G-proteins through catalytic replacement of GDP by GTP. During nucleotide exchange, three distinct substrate·enzyme complexes occur: a ternary complex with GDP at the start of the reaction (G-protein·GEF·GDP), an intermediary nucleotide-free binary complex (G-protein·GEF), and a ternary GTP complex after productive G-protein activation (G-protein·GEF·GTP). Here, we show structural snapshots of the full nucleotide exchange reaction sequence together with the G-protein substrates and products using Rabin8/GRAB (GEF) and Rab8 (G-protein) as a model system. Together with a thorough enzymatic characterization, our data provide a detailed view into the mechanism of Rabin8/GRAB-mediated nucleotide exchange.

Extracellular acidosis contracts coronary but neither renal nor mesenteric artery via modulation of H+,K+-ATPase, voltage-gated K+ channels and L-type Ca2+ channels.

Extracellular acidosis (EA) jeopardizes the heart, whereas mild extracellular alkalinization is cardioprotective, but it remains elusive how the coronary artery (CA) responses to EA. In the present study, EA was demonstrated to induce contraction in rat coronary artery (RCA) in a manner dependent on extracellular pH (pHo, 7.2-6.6), whereas it did not affect the resting tone of either rat renal interlobe artery (RIA) or mesenteric artery (MA). The amplitude of contraction provoked by pHo 6.8 was approximately equal to that induced by 60 mmol l(-1) KCl at pHo 7.4. Blockade of L-type voltage-gated Ca(2+) channels and inhibition of H(+),K(+)-ATPase attenuated the contraction, whereas inhibition of nitric oxide synthesis and endothelial denudation augmented it. A molecular probe study showed that EA acidified the cytosol of arterial smooth muscle cells (ASMCs) in RIA and MA, but alkalinized it in RCA. Extracellular acidosis elevated the intracellular Ca(2+) concentration exclusively in RCA ASMCs. Patch-clamp studies showed that EA enhanced L-type voltage-gated Ca(2+) channel currents in RCA ASMCs, but depressed the currents in MA ASMCs and did not affect the currents in RIA ASMCs. Extracellular acidosis depressed voltage-gated K(+) channel (KV) currents only in RCA ASMCs. Lansoprazole blunted all these observed effects of EA on RCA. Taken together, the present results demonstrate that the responses of RCA to EA are different from those of RIA and MA and suggest that activation of L-type voltage-gated Ca(2+) channels and H(+),K(+)-ATPase as well as depression of KV may, at least partly, underlie the EA-induced contraction in RCA.