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1.
Glycolipid transfer protein (GLTP) accelerates glycosphingolipid (GSL) intermembrane transfer via a unique lipid transfer/binding fold (GLTP-fold) that defines the GLTP superfamily and is the prototype for GLTP-like domains in larger proteins, i.e. phosphoinositol 4-phosphate adaptor protein-2 (FAPP2). Although GLTP-folds are known to play roles in the nonvesicular intracellular trafficking of glycolipids, their ability to alter cell phenotype remains unexplored. In the present study, overexpression of human glycolipid transfer protein (GLTP) was found to dramatically alter cell phenotype, with cells becoming round between 24 and 48 h after transfection. By 48 h post transfection, ~70% conversion to the markedly round shape was evident in HeLa and HEK-293 cells, but not in A549 cells. In contrast, overexpression of W96A-GLTP, a liganding-site point mutant with abrogated ability to transfer glycolipid, did not alter cell shape. The round adherent cells exhibited diminished motility in wound healing assays and an inability to endocytose cholera toxin but remained viable and showed little increase in apoptosis as assessed by poly(ADP-ribose) polymerase cleavage. A round cell phenotype also was induced by overexpression of FAPP2, which binds/transfers glycolipid via its C-terminal GLTP-like fold, but not by a plant GLTP ortholog (ACD11), which is incapable of glycolipid binding/transfer. Screening for human protein partners of GLTP by yeast two hybrid screening and by immuno-pulldown analyses revealed regulation of the GLTP-induced cell rounding response by interaction with δ-catenin. Remarkably, while δ-catenin overexpression alone induced dendritic outgrowths, coexpression of GLTP along with δ-catenin accelerated transition to the rounded phenotype. The findings represent the first known phenotypic changes triggered by GLTP overexpression and regulated by direct interaction with a p120-catenin protein family member. 相似文献
2.
Glycolipid transfer proteins (GLTPs) were first identified over three decades ago as ~24kDa, soluble, amphitropic proteins that specifically accelerate the intermembrane transfer of glycolipids. Upon discovery that GLTPs use a unique, all-α-helical, two-layer ‘sandwich’ architecture (GLTP-fold) to bind glycosphingolipids (GSLs), a new protein superfamily was born. Structure/function studies have provided exquisite insights defining features responsible for lipid headgroup selectivity and hydrophobic ‘pocket’ adaptability for accommodating hydrocarbon chains of differing length and unsaturation. In humans, evolutionarily-modified GLTP-folds have been identified with altered sphingolipid specificity, e. g. ceramide-1-phosphate transfer protein (CPTP), phosphatidylinositol 4-phosphate adaptor protein-2 (FAPP2) which harbors a GLTP-domain and GLTPD2. Despite the wealth of structural data (>40 Protein Data Bank deposits), insights into the in vivo functional roles of GLTP superfamily members have emerged slowly. In this review, recent advances are presented and discussed implicating human GLTP superfamily members as important regulators of: i) pro-inflammatory eicosanoid production associated with Group-IV cytoplasmic phospholipase A2; ii) autophagy and inflammasome assembly that drive surveillance cell release of interleukin-1β and interleukin-18 inflammatory cytokines; iii) cell cycle arrest and necroptosis induction in certain colon cancer cell lines. The effects exerted by GLTP superfamily members appear linked to their ability to regulate sphingolipid homeostasis by acting in either transporter and/or sensor capacities. These timely findings are opening new avenues for future cross-disciplinary, translational medical research involving GLTP-fold proteins in human health and disease. Such avenues include targeted regulation of specific GLTP superfamily members to alter sphingolipid levels as a therapeutic means for combating viral infection, neurodegenerative conditions and circumventing chemo-resistance during cancer treatment. 相似文献
3.
《生物化学与生物物理学报:生物膜》2018,1860(5):1069-1076
HET-C2 is a fungal glycolipid transfer protein (GLTP) that uses an evolutionarily-modified GLTP-fold to achieve more focused transfer specificity for simple neutral glycosphingolipids than mammalian GLTPs. Only one of HET-C2's two Trp residues is topologically identical to the three Trp residues of mammalian GLTP. Here, we provide the first assessment of the functional roles of HET-C2 Trp residues in glycolipid binding and membrane interaction. Point mutants HET-C2W208F, HET-C2W208A and HET-C2F149Y all retained > 90% activity and 80–90% intrinsic Trp fluorescence intensity; whereas HET-C2F149A transfer activity decreased to ~ 55% but displayed ~ 120% intrinsic Trp emission intensity. Thus, neither W208 nor F149 is absolutely essential for activity and most Trp emission intensity (~ 85–90%) originates from Trp109. This conclusion was supported by HET-C2W109Y/F149Y which displayed ~ 8% intrinsic Trp intensity and was nearly inactive. Incubation of the HET-C2 mutants with 1-palmitoyl-2-oleoyl-phosphatidylcholine vesicles containing different monoglycosylceramides or presented by lipid ethanol-injection decreased Trp fluorescence intensity and blue-shifted the Trp λmax by differing amounts compared to wtHET-C2. With HET-C2 mutants for Trp208, the emission intensity decreases (~ 30–40%) and λmax blue-shifts (~ 12 nm) were more dramatic than for wtHET-C2 or F149 mutants and closely resembled human GLTP. When Trp109 was mutated, the glycolipid induced changes in HET-C2 emission intensity and λmax blue-shift were nearly nonexistent. Our findings indicate that the HET-C2 Trp λmax blue-shift is diagnostic for glycolipid binding; whereas the emission intensity decrease reflects higher environmental polarity encountered upon nonspecific interaction with phosphocholine headgroups comprising the membrane interface and specific interaction with the hydrated glycolipid sugar. 相似文献
4.
Kamlekar RK Gao Y Kenoth R Molotkovsky JG Prendergast FG Malinina L Patel DJ Wessels WS Venyaminov SY Brown RE 《Biophysical journal》2010,99(8):2626-2635
Human glycolipid transfer protein (GLTP) serves as the GLTP-fold prototype, a novel, to our knowledge, peripheral amphitropic fold and structurally unique lipid binding motif that defines the GLTP superfamily. Despite conservation of all three intrinsic Trps in vertebrate GLTPs, the Trp functional role(s) remains unclear. Herein, the issue is addressed using circular dichroism and fluorescence spectroscopy along with an atypical Trp point mutation strategy. Far-ultraviolet and near-ultraviolet circular dichroism spectroscopic analyses showed that W96F-W142Y-GLTP and W96Y-GLTP retain their native conformation and stability, whereas W85Y-W96F-GLTP is slightly altered, in agreement with relative glycolipid transfer activities of >90%, ∼85%, and ∼45%, respectively. In silico three-dimensional modeling and acrylamide quenching of Trp fluorescence supported a nativelike folding conformation. With the Trp96-less mutants, changes in emission intensity, wavelength maximum, lifetime, and time-resolved anisotropy decay induced by phosphoglyceride membranes lacking or containing glycolipid and by excitation at different wavelengths along the absorption-spectrum red edge indicated differing functions for W142 and W85. The data suggest that W142 acts as a shallow-penetration anchor during docking with membrane interfaces, whereas the buried W85 indole helps maintain proper folding and possibly regulates membrane-induced transitioning to a glycolipid-acquiring conformation. The findings illustrate remarkable versatility for Trp, providing three distinct intramolecular functions in the novel amphitropic GLTP fold. 相似文献
5.
Xiuhong Zhai William E. Momsen Dmitry A. Malakhov Ivan A. Boldyrev Maureen M. Momsen Julian G. Molotkovsky Howard L. Brockman Rhoderick E. Brown 《Journal of lipid research》2013,54(4):1103-1113
Among amphitropic proteins, human glycolipid transfer protein (GLTP) forms a structurally-unique fold that translocates on/off membranes to specifically transfer glycolipids. Phosphatidylcholine (PC) bilayers with curvature-induced packing stress stimulate much faster glycolipid intervesicular transfer than nonstressed PC bilayers raising questions about planar cytosol-facing biomembranes being viable sites for GLTP interaction. Herein, GLTP-mediated desorption kinetics of fluorescent glycolipid (tetramethyl-boron dipyrromethene (BODIPY)-label) from lipid monolayers are assessed using a novel microfluidics-based surface balance that monitors lipid lateral packing while simultaneously acquiring surface fluorescence data. At biomembrane-like packing (30–35 mN/m), GLTP uptake of BODIPY-glycolipid from POPC monolayers was nearly nonexistent but could be induced by reducing surface pressure to mirror packing in curvature-stressed bilayers. In contrast, 1-palmitoyl-2-oleoyl-phosphatidylethanolamine (POPE) matrices supported robust BODIPY-glycolipid uptake by GLTP at both high and low surface pressures. Unexpectedly, negatively-charged cytosol-facing lipids, i.e., phosphatidic acid and phosphatidylserine, also supported BODIPY-glycolipid uptake by GLTP at high surface pressure. Remarkably, including both 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphate (5 mol%) and POPE (15 mol%) in POPC synergistically activated GLTP at high surface pressure. Our study shows that matrix lipid headgroup composition, rather than molecular packing per se, is a key regulator of GLTP-fold function while demonstrating the novel capabilities of the microfluidics-based film balance for investigating protein-membrane interfacial interactions. 相似文献
6.
Wu SP Bellei M Mansy SS Battistuzzi G Sola M Cowan JA 《Journal of inorganic biochemistry》2011,105(6):806-811
Schizosaccharomyces pombe (Sp) ferredoxin contains a C-terminal electron transfer protein ferredoxin domain (etpFd) that is homologous to adrenodoxin. The ferredoxin has been characterized by spectroelectrochemical methods, and Mössbauer, UV-Vis and circular dichroism spectroscopies. The Mössbauer spectrum is consistent with a standard diferric [2Fe-2S]2+ cluster. While showing sequence homology to vertebrate ferredoxins, the E°' and the reduction thermodynamics for etpFd (− 0.392 V) are similar to plant-type ferredoxins. Relatively stable Cys to Ser derivatives were made for each of the four bound Cys residues and variations in the visible spectrum in the 380-450 nm range were observed that are characteristic of oxygen ligated clusters, including members of the [2Fe-2S] cluster IscU/ISU scaffold proteins. Circular dichroism spectra were similar and consistent with no significant structural change accompanying these mutations. All derivatives were active in an NADPH-Fd reductase cytochrome c assay. The binding affinity of Fd to the reductase was similar, however, Vmax reflecting rate limiting electron transfer was found to decrease ~ 13-fold. The data are consistent with relatively minor perturbations of both the electronic properties of the cluster following substitution of the Fe-bond S atom with O, and the electronic coupling of the cluster to the protein. 相似文献
7.
The glycolipid transfer protein (GLTP)-mediated movement of galactosylceramide from model membrane donor vesicles to acceptor vesicles is sensitive to the membrane environment surrounding the glycolipid. GLTP can catalyze the transfer of a fluorescently labeled GSL, anthrylvinyl-galactosylceramide (AV-GalCer), from vesicles composed of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine and dipalmitoylphosphatidylcholine matrices, but not from vesicles prepared from N-palmitoylsphingomyelin, regardless of the cholesterol content of the vesicles. In this study, we have examined the structural features of sphingomyelin (SM) that are responsible for its inhibition of the rate of GLTP-catalyzed transfer of AV-GalCer. The rate of glycolipid transfer was enhanced when the N-palmitoyl chain of SM was replaced with an N-oleoyl chain. Analogs of N-palmitoyl-SM in which the 4,5-double bond of the long-chain base is reduced or the 3-hydroxy group is removed did not inhibit GLTP-catalyzed transfer of AV-GalCer. When the donor vesicles were prepared with phosphatidylcholines or ether-linked phosphatidylcholine analogs, the transfer rates of AV-GalCer increased with increasing degree of unsaturation. The rate of AV-GalCer transfer was strongly dependent on the unsaturation degree of the acyl and/or alkyl chains. For ester-linked PCs, the transfer rate increased in the order DPPC < POPC < DOPC, which have 0, 1, and 2 cis double bonds, respectively. 相似文献
8.
Xiuhong Zhai Margarita L. Malakhova Helen M. Pike Linda M. Benson H. Robert Bergen III Istv��n P. Sug��r Lucy Malinina Dinshaw J. Patel Rhoderick E. Brown 《The Journal of biological chemistry》2009,284(20):13620-13628
Glycolipid transfer proteins (GLTPs) are small, soluble proteins that
selectively accelerate the intermembrane transfer of glycolipids. The GLTP
fold is conformationally unique among lipid binding/transfer proteins and
serves as the prototype and founding member of the new GLTP superfamily. In
the present study, changes in human GLTP tryptophan fluorescence, induced by
membrane vesicles containing glycolipid, are shown to reflect glycolipid
binding when vesicle concentrations are low. Characterization of the
glycolipid-induced “signature response,” i.e. ∼40%
decrease in Trp intensity and ∼12-nm blue shift in emission wavelength
maximum, involved various modes of glycolipid presentation, i.e.
microinjection/dilution of lipid-ethanol solutions or phosphatidylcholine
vesicles, prepared by sonication or extrusion and containing embedded
glycolipids. High resolution x-ray structures of apo- and holo-GLTP indicate
that major conformational alterations are not responsible for the
glycolipid-induced GLTP signature response. Instead, glycolipid binding alters
the local environment of Trp-96, which accounts for ∼70% of total emission
intensity of three Trp residues in GLTP and provides a stacking platform that
aids formation of a hydrogen bond network with the ceramide-linked sugar of
the glycolipid headgroup. The changes in Trp signal were used to
quantitatively assess human GLTP binding affinity for various lipids including
glycolipids containing different sugar headgroups and homogenous acyl chains.
The presence of the glycolipid acyl chain and at least one sugar were
essential for achieving a low-to-submicromolar dissociation constant that was
only slightly altered by increased sugar headgroup complexity.Glycolipid transfer protein
(GLTP)4 is a soluble
(∼24-kDa) protein that selectively transfers glycosphingolipids (GSLs)
between membranes. GSLs play key roles in cell recognition, adhesion,
differentiation, proliferation, and programmed death in normal and disease
states
(1–8).
Phylogenetic/evolutionary analyses show GLTP to be highly conserved among
vertebrates
(9–11).
The conformational uniqueness of the GLTP fold when compared with other lipid
binding/transfer proteins
(12–14)
has resulted in GLTP being designated the prototype and founding member of the
GLTP superfamily (15,
16). GLTP employs a novel
two-layer “sandwich motif,” dominated by α-helices and
achieved without intramolecular disulfide bridges, to accommodate glycolipid
within a single lipid binding site and to form a membrane-interaction domain
that differs from other known membrane targeting/translocation domains,
i.e. C1, C2, PH, PX, and FYVE
(9,
13,
17–21).
The glycolipid binding site of GLTP consists of a sugar headgroup recognition
center that anchors the ceramide-linked sugar to the protein surface via
multiple hydrogen bonds and a hydrophobic tunnel that accommodates the
hydrocarbon chains of ceramide. The crystal structures of glycolipid-free GLTP
and of GLTP complexed with a half-dozen glycolipids differing in sugar
headgroup and/or lipid acyl composition reveal the basis for specific
recognition and adaptive accommodation of various GSLs. A conserved, concerted
sequence of events, initiated by anchoring of the GSL headgroup to the sugar
headgroup recognition center, seems to facilitate entry and exit of the lipid
chains in the membrane-associated state
(13). Glycolipid uptake occurs
via a cleft-like gating mechanism involving conformational changes to one
α-helix and two interhelical loops
(12). The selectivity of GLTP
for glycolipids makes this protein a prime candidate for molecular
manipulation of GSL-enriched microdomains in membranes as well as a potential
vehicle for selectively delivering glycolipids to cells. However, the binding
affinity of various glycolipids for GLTP and the time frame of GSL uptake by
GLTP remain unclear. In the present study, these issues are investigated using
fluorescence approaches.GLTP is intrinsically fluorescent by virtue of having 3 Trp and 10 Tyr
residues among its 209 amino acids. All 3 Trp residues reside on or near the
surface of GLTP
(12–14,
17,
22,
23), where they could help
form a membrane-interaction site. Only one, Trp-96, is directly involved in
glycolipid binding
(12–14).
Given the likely roles in membrane interaction and GSL binding, our goal was
to define the relative contributions of the Trp fluorescence changes caused by
membrane interaction versus glycolipid binding. A signature Trp
emission response, indicative of GSL binding by WT-GLTP, has been identified
and characterized using select GLTP point mutants and different modes of
glycolipid presentation, i.e. ethanol injection of pure GSLs and
titration with membrane vesicles (LUVs and SUVs) containing GSLs as minor
components. The signature Trp emission response has been used to
comprehensively assess the glycolipid binding affinity of the novel GLTP fold
for the first time, focusing on the impact of compositional variation of the
sugar headgroup and nonpolar acyl chain moieties of the glycolipid. 相似文献
9.
Sunny Huang 《Inorganica chimica acta》2005,358(4):885-890
The oxidation of Ru(NH3)5NCCH2CN2+ complex by the peroxydisulfate ion in the aqueous solution yields two products, Ru(NH3)5NHCOCH2CN2+ with λmax = 373 nm and withλmax = 863 nm. The distribution of the products and the amount of oxidant required for the maximum yield of the binuclear complex depend on the acidity of the solution. The production of the binuclear complex was favored at lower acid concentrations. The formation of CC bond in the binuclear complex was characterized by both the spectral and the electrochemical results. A mechanism for the oxidation has been proposed by the kinetic studies in the region of 0.001-0.10 M acid concentrations. 相似文献
10.
Ma B Zhang Q Wang G Wu Z Shaw JP Hu Y Wang Y Zheng Y Yang Z Ying H 《Journal of inorganic biochemistry》2011,105(4):563-568
A novel strontium compound has been synthesized by the reaction of fructose-1,6-diphosphate with strontium (Sr-FDP). The compound was characterized and confirmed with elemental analyses and spectroscopic (IR, NMR) methods. The pharmacokinetic profiles of Sr-FDP were investigated in Sprague-Dawley rats following oral administration at a dose of 110, 220, and 440 mg/kg respectively. Pharmacokinetic differences were also compared in intact rats and ovariectomized rats with and without estrogen supplement. Strontium concentrations in plasma, urine, tissue and feces were determined by graphite furnace atomic absorption spectroscopy (GFAAS). The results showed that Sr-FDP was absorbed rapidly with Tmax < 1 h in all the groups with AUC0-∞ proportional to the oral dose. The pharmacokinetic profiles were characterized by long half-life, a large apparent volume of distribution. The highest Sr concentration was observed in the bone at 6 h, and the level of Sr decreased close to the baseline in heart, liver, spleen, lung, intestine, brain and kidney after 12 h. The cumulative amounts of Sr over 96 h were found to be ~ 3% in urine, but ~ 70% in feces suggesting that the parent drug was mainly excreted from the intestine. The Cmax and AUC0-∞ of Sr-FDP in ovariectomized rats were significantly decreased compared to those in intact rats, and this trend was ameliorated by using 17-beta-estradiol (E2) treatment in the ovariectomized rats. 相似文献
11.
Lanthanide complexes are of great importance for their prospective applications in wide range of science and technology. Chiral lanthanide complexes can constitute stereo-discriminating probes in biological media, owing to the luminescent properties of the rare-earth ions. Sensitized emission with narrow bandwidth, having fast radiation rate and high emission quantum efficiency are the main perspective for synthesizing the complexes. Attention has been given on remarkable chirality with high dissymmetry factors (g = Δεext/εmax) of the complexes. For this purpose, beta-diketonato ligands with chiral BINAPO (1,1′-binapthyl phosphine oxide) ligand were chosen to achieve the goal. The complexes [Ln(TFN)3(S-BINAPO)](TFN = 4,4,4-trifluoro-1(2-napthyl)-1,3-butanedione), [Ln(HFT)3(S-BINAPO)] (HFT = 4,4,5,5,6,6,6-heptafluoro-1-(2-thienyl)-1,3-hexanedione) and [Ln(HFA)3(S-BINAPO)](hfa = hexafluoroacetylacetonate) (where Ln = Yb, Eu) were synthesized. The complex, [Eu(TFN)3(S-BINAPO)] gives strong red emission at 615 nm with narrow emission band (<10 nm) when excited by 465 nm light with quantum efficiency 86%. The dissymmetry factors (g = Δεext/εmax) corresponding to the 7F1 → 5D0 transition at 590 nm is 0.091 for [Eu(TFN)3(S-BINAPO)] and for [Yb(hfa)3(S-BINAPO)](hfa = hexafluoroacetylacetonate) corresponding to the 2F7/2 → 2F5/2 transitions is 0.12, are among the largest values for both Eu and Yb complexes to date, respectively. The Eu complexes, [Eu(HFT)3(S-BINAPO)] and [Eu(TFN)3(S-BINAPO)] are found to be spontaneously emissive, showing bright red emission, when placed in sunlight or even in the laboratory when light is switched on. 相似文献
12.
Belinda B.B. Guo Renwick C.J. Dobson Juliet A. Gerrard 《Biochemical and biophysical research communications》2009,380(4):802-806
Dihydrodipicolinate synthase (DHDPS) catalyses the first committed step in the biosynthesis of (S)-lysine, an essential constituent of bacterial cell walls. Escherichia coli DHDPS is homotetrameric, and each monomer contains an N-terminal (β/α)8-barrel, responsible for catalysis and regulation, and three C-terminal α-helices, the function of which is unknown. This study investigated the C-terminal domain of E. coli DHDPS by characterising a C-terminal truncated DHDPS (DHDPS-H225∗). DHDPS-H225∗ was unable to complement an (S)-lysine auxotroph, and showed significantly reduced solubility, stability, and maximum catalytic activity (kcat = 1.20 ± 0.01 s−1), which was only 1.6% of wild type E. coli DHDPS (DHDPS-WT). The affinity of DHDPS-H225∗ for substrates and the feedback inhibitor, (S)-lysine, remained comparable to DHDPS-WT. These changes were accompanied by disruption in the quaternary structure, which has previously been shown to be essential for efficient catalysis in this enzyme. 相似文献
13.
S. Max Bessey 《Inorganica chimica acta》2010,363(1):279-7422
The synthesis of triethylphosphine gold(I) 4-nitrobenzenethiolate, Et3PAu(SC6H4NO2-4), is reported. Et3PAu(SC6H4NO2-4) displays a low energy visible electronic absorption band which is solvent dependent: EtOH (λmax = 385 nm), acetonitrile (λmax = 391 nm), THF (λmax = 395 nm), and DMSO (λmax = 402 nm). The corresponding low energy visible electronic absorption band of 4-nitrobenzenethiolate, 4-NO2C6H4S− also shows solvent dependency: acetonitrile, (λmax = 484 nm), DMSO (λmax = 502 nm), dimethylformamide (λmax = 505 nm). The positive solvatochromic shifts for Et3PAu(SC6H4NO2-4) and 4-NO2C6H4S− are consistent with an intraligand (IL) charge transfer transition, i.e. π(S) → ∗π (C6H4NO2-4) or n(S) → ∗π (C6H4NO2-4). Assignment of 4-NO2C6H4S− was aided by a DFT calculation. 相似文献
14.
Polydentate nitrogen heterocycle ligand 2,3-bis(2-pyridyl)pyrazine (2,3-dpp) reacted with M(NO3)x (M = Ag, x = 1; M = Cd, x = 2) to give two new complexes [Ag(2,3-dpp)(NO3)]2 (1) and [Cd(2,3-dpp)(NO3)2]n (2). Both complexes have been characterized by single-crystal X-ray diffraction, elemental analyses, IR and 1H NMR spectroscopy. Single-crystal X-ray analyses showed that complex 1 crystallized in monoclinic, space group P21/n is a dimmer containing penta-coordinated Ag+ ion. While compound 2 has 1D chain-like structure with repeat unit Cd(2,3-dpp)(NO3)2, in which the Cd(II) presents octa-coordinated N4O4 donor set with two four-membered chelating rings and two five-membered chelating rings around Cd(II) ion. Meanwhile, every neutral chain [Cd(2,3-dpp)(NO3)2]n is mutually connected by face-to-face π?π packing interactions to form a two dimensional layer. Furthermore, antibacterial activities of compound 1 and luminescent property of the compound 2 are also investigated. 相似文献
15.
Maximilian N. Kopylovich Kamran T. Mahmudov Konstantin V. Luzyanin 《Inorganica chimica acta》2011,374(1):175-579
(E)-2-(2-(2-hydroxyphenyl)hydrazono)-1-phenylbutane-1,3-dione (H2L) was synthesized by azocoupling of diazonium salt of 2-hydroxyaniline with 1-phenylbutane-1,3-dione and characterized by IR, 1H and 13C NMR spectroscopies and X-ray diffraction analysis. In solution, H2L exists as a mixture of the enol-azo and hydrazone tautomeric forms and a decrease of temperature and of solvent polarity shifts the tautomeric balance to the hydrazone form. In the solid state, H2L crystallizes from ethanol-water in the monohydrate hydrazone form, as shown by X-ray analysis. The dissociation constants of H2L (pK1 = 5.98 ± 0.04, pK2 = 9.72 ± 0.03) and the stability constants of its copper(II) complex (log β1 = 11.01 ± 0.07, log β2 = 20.19 ± 0.08) were determined by the potentiometric method in aqueous-ethanol solution. The copper(II) complex [Cu2(μ-L)2]n was isolated in the solid state and found by X-rays to be a coordination polymer of a binuclear core with a distorted square pyramidal metal coordination geometry. 相似文献
16.
Calmodulin (CaM) binding to the intracellular C-terminal tail (CTT) of the cardiac L-type Ca2+ channel (CaV1.2) regulates Ca2+ entry by recognizing sites that contribute to negative feedback mechanisms for channel closing. CaM associates with CaV1.2 under low resting [Ca2+], but is poised to change conformation and position when intracellular [Ca2+] rises. CaM binding Ca2+, and the domains of CaM binding the CTT are linked thermodynamic functions. To better understand regulation, we determined the energetics of CaM domains binding to peptides representing pre-IQ sites A1588, and C1614 and the IQ motif studied as overlapping peptides IQ1644 and IQ′1650 as well as their effect on calcium binding. (Ca2+)4-CaM bound to all four peptides very favorably (Kd ≤ 2 nM). Linkage analysis showed that IQ1644-1670 bound with a Kd ~ 1 pM. In the pre-IQ region, (Ca2+)2-N-domain bound preferentially to A1588, while (Ca2+)2-C-domain preferred C1614. When bound to C1614, calcium binding in the N-domain affected the tertiary conformation of the C-domain. Based on the thermodynamics, we propose a structural mechanism for calcium-dependent conformational change in which the linker between CTT sites A and C buckles to form an A-C hairpin that is bridged by calcium-saturated CaM. 相似文献
17.
The heme-based oxygen-sensor enzyme from Escherichia coli (Ec DOS) is a heme-regulated phosphodiesterase with activity on cyclic-di-GMP and is composed of an N-terminal heme-bound sensor domain with the PAS structure and a C-terminal functional domain. The activity of Ec DOS is substantially enhanced by the binding of O2 to the Fe(II)-protoporphyrin IX complex [Fe(II) complex] in the sensor domain. The binding of O2 to the Fe(II) complex changes the structure of the sensor domain, and this altered structure becomes a signal that is transduced to the functional domain to trigger catalysis. The first step in intra-molecular signal transduction is the binding of O2 to the Fe(II) complex, and detailed elucidation of this molecular mechanism is thus worthy of exploration. The X-ray crystal structure reveals that Phe113 is located close to the O2 molecule bound to the Fe(II) complex in the sensor domain. Here, we found that the O2 association rate constants (>200 × 10−3 μM−1 s−1: F113L; 26 × 10−3 μM−1 s−1: F113Y) of the Fe(II) complexes of Phe113 mutants were markedly different from that (51 × 10−3 μM−1 s−1) of the wild-type enzyme, and auto-oxidation rates (0.00068 min−1: F113L; 0.039 min−1: F113Y) of the Phe113 mutants also differed greatly from that (0.0062 min−1) of the wild-type enzyme. We thus suggest that Phe113, residing near the O2 molecule, has a critical role in optimizing the Fe(II)-O2 complex for effective regulation of catalysis by the oxygen-sensor enzyme. Interactions of CO and cyanide anion with the mutant proteins were also studied. 相似文献
18.
Yolanda Pérez Isabel Sierra Mariano Fajardo Isabel del Hierro 《Inorganica chimica acta》2007,360(2):607-618
In view of the wide applicability and versatility of titanium based Lewis acids in selective organic synthesis including asymmetric synthesis, we have synthesized a family of mono and polyatomic titanium derivatives. The polymetallic complexes prepared are bridged by pyridimine, quinone and triazine based ligands. The synthesis of [{Ti(O-i-Pr)3(Oddbf)}2] (1), [Ti(O-i-Pr)2(Oddbf)2] (2), [{Ti(O-i-Pr)2(Oddbf)(OMent)}2] (3) (ddbfO = 2,3-dihydro-2,2-dimethyl-benzofuranoxo; MentO = (1R,2S,5R)-(−)-menthoxo), [{Ti(O-i-Pr)3(OMenpy)}2] (4), [Ti(O-i-Pr)2(OMenpy)2] (5) (MenpyO = (1S,2S,5R)-(−)-menthoxo-pyridine); [{(Ti(OR)3)2L}n] (RO = isopropoxo, (1R,2S,5R)-(−)-menthoxo) (6-11) and [{(Ti(O-i-Pr)3)3L}n] (12) was accomplished from a Lewis acid such as Ti(O-i-Pr)4, [{Ti(O-i-Pr)3(OMent)}2] or [Ti(OMent)4] and chelating ligands (ddbfOH = 2,3-dihydro-2,2-dimethyl-benzofuranol; MenpyOH = (1R,2S,5R)-(−)-5-methyl-2-isopropyl-1-(2′-pyridinyl)cyclohexan-1-ol; LH2 = 4,6-dihydroxy-2,5-diphenyl-pyrimidine, 2,4-dihydroxy-5,6-dimethyl-pyrimidine, 5,8-dihydroxy-1,4-napthoquinone, 2,5-dihydroxy-1,4-benzoquinone and LH3 = cyanuric acid) that provide a rigid framework for the metal centre. The molecular structure of 5 has been determined by single crystal X-ray diffraction studies. 相似文献
19.
Mónica M. Vergara Florencia Fagalde Jan Fiedler Monika Sieger 《Inorganica chimica acta》2010,363(1):163-2714
New diruthenium complexes (PPN)4[(NC)4Ru(μ-bptz)Ru(CN)4], (PPN)41, and [(bpy)2Ru(μ-bptz)Ru(CN)4], 2, (PPN+ = bis(triphenylphospine)iminium; bptz = 3,6-bis(2-pyridyl)-1,2,4,5-tetrazine; bpy = 2,2′-bipyridine), were synthesised and characterised by spectroscopic and electrochemical techniques. The comproportionation constant Kc = 107.0 of the mixed-valent species [(NC)4Ru(μ-bptz)Ru(CN)4]3− as obtained by oxidation of 14− in CH3CN is much lower than the Kc = 1015.0 previously detected for [(H3N)4Ru(bptz)Ru(NH3)4]5+, reflecting the competition between CN− and bptz for the π-electron density of the metals. Comparison with several other bptz-bridged diruthenium(II,III) complexes reveals an approximate correlation between Kc and the diminishing effective π acceptor capacity of the ancillary terminal ligands. In addition to the intense MLCT absorption at λmax = 624 nm, the main IVCT (intervalence charge transfer) band of 13− was detected by spectroelectrochemistry at λmax = 1695 nm (in CH3CN; ε = 3200 M−1 cm−1). The experimental band width at half-height, Δν1/2 = 2700 cm−1, is slightly smaller than the theoretical value Δν1/2 = 3660 cm−1, calculated from the Hush approximation for Class II mixed-valent species. In agreement with comparatively moderate metal-metal coupling, the mixed-valent intermediate 13− was found to be EPR silent even at 4 K. The unsymmetrical mixed-valent complex [(bpy)2RuII(μ-bptz)RuIII(CN)4]+, obtained in situ by bromine oxidation of 2 in CH3CN/H2O, displays a broad NIR absorption originating from an IVCT transition at λmax = 1075 nm (ε ≈ 1000 M−1 cm−1, Δν1/2 ≈ 4000 cm−1). In addition, the lifetime of the excited-state of the mononuclear precursor complex [Ru(bptz)(CN)4]2− was measured in H2O by laser flash photolysis; the obtained value of τ = 19.6 ns reveals that bptz induces a metal-to-ligand electronic delocalisation effect intermediate between that induced by bpy and bpz (bpz = 2,2′-bipyrazine) in analogous tetracyanoruthenium complexes. 相似文献
20.
The reaction of 2-benzoylpyridine-N(4)-cyclohexylthiosemicarbazone [HBPCT, (1)] ligand with organotin(IV) chloride(s) lead to the formation of three new organotin(IV) complexes: [MeSnCl2(BPCT)] (2), [PhSnCl2(BPCT)] (3) and [Ph2SnCl(BPCT)] (4). The ligand (1) and its organotin(IV) complexes (2-4) have been synthesized and characterized by CHN analyses, molar conductivity, UV-Vis, FT-IR and 1H NMR spectral studies. The single crystal X-ray diffraction studies indicated that [PhSnCl2(BPCT)] (3) is six coordinated and adopts strongly a distorted octahedral configuration with the coordination through pyridine-N, azomethine-N and thiolato-S atoms of the ligand. The crystal system of [PhSnCl2(BPCT)] (3) is orthorhombic with space group P2ac2n and the unit cell dimensions: a = 28.1363(5) Å, b = 9.5970(2) Å, c = 9.4353(2) Å. 相似文献