Fiber optic magnetic field sensor using Co doped ZnO nanorods as cladding

A fiber optic magnetic field sensor is proposed and experimentally demonstrated. Pristine and Co doped ZnO nanorods of different Co concentrations (5, 10, 15 and 20 at%) were synthesized using a hydrothermal method. The synthesized nanorods were subjected to various characterization methods like X-ray diffraction (XRD), optical absorption, scanning electron microscopy, energy dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy, vibrating sample magnetometry and X-ray photoelectron spectroscopy (XPS). XRD and XPS analysis confirms that the Co ions were successfully incorporated into the Zn site of the wurtzite ZnO lattice without altering the structure. The pristine and Co doped ZnO nanorods showed remarkable changes in the M–H loop where the diamagnetic behavior of ZnO changes to paramagnetic when doped with Co. The sensor structure is composed of cladding modified fiber coated with Co doped ZnO nanorods as a sensing material. The modified cladding is proportionally sensitive to the ambient magnetic field because of the magneto-optic effect. Experimental results revealed that the sensor has an operating magnetic field range from 17 mT to 180 mT and shows a maximum sensitivity of ∼18% for 15 at% Co doped ZnO nanorods. The proposed magnetic field sensor would be attractive due to its low cost fabrication, simplicity of the sensor head preparation, high sensitivity and reproducibility.

A fiber optic magnetic field sensor based on Co doped ZnO nanorods is proposed and demonstrated. The sensor has an operating magnetic field range of 17 mT to 180 mT and shows a maximum sensitivity of ∼18% for 15 at% Co doped ZnO nanorods.

Synthesis of Zn1−xCdxO Nanoparticles by Co-Precipitation: Structural, Optical and Photodetection Analysis

Zinc oxide (ZnO) is a wide bandgap semiconductor with excellent photoresponse in ultra-violet (UV) regime. Tuning the bandgap of ZnO by alloying with cadmium can shift its absorption cutoff wavelength from UV to visible (Vis) region. Our work aims at synthesis of Zn[Formula: see text]CdxO nanoparticles by co-precipitation method for the fabrication of photodetector. The properties of nanoparticles were analyzed using X-ray diffractometer, UV–Vis spectrometer, scanning electron microscope and energy dispersive spectrometer. The incorporation of cadmium without altering the wurtzite structure resulted in the red shift in the absorption edge of ZnO. Further, the photoresponse characteristics of Zn[Formula: see text]CdxO nanopowders were investigated by fabricating photodetectors. It has been found that with Cd alloying the photosensitivity was increased in the UVA-violet as well in the blue region.

Multi-band visible photoresponse study of Co2+ doped ZnO nanoparticles

Cobalt doping enhances visible absorption in ZnO nanoparticles as a result of d–d transitions. By co-precipitation method, Zn_1−xCo_xO nanoparticles had been synthesised and multiband photodetectors were fabricated after characteristic analysis.

A multidrug ABC transporter with a taste for salt

BACKGROUND

LmrA is a multidrug ATP-binding cassette (ABC) transporter from Lactococcus lactis with no known physiological substrate, which can transport a wide range of chemotherapeutic agents and toxins from the cell. The protein can functionally replace the human homologue ABCB1 (also termed multidrug resistance P-glycoprotein MDR1) in lung fibroblast cells. Even though LmrA mediates ATP-dependent transport, it can use the proton-motive force to transport substrates, such as ethidium bromide, across the membrane by a reversible, H(+)-dependent, secondary-active transport reaction. The mechanism and physiological context of this reaction are not known.

METHODOLOGY/PRINCIPAL FINDINGS

We examined ion transport by LmrA in electrophysiological experiments and in transport studies using radioactive ions and fluorescent ion-selective probes. Here we show that LmrA itself can transport NaCl by a similar secondary-active mechanism as observed for ethidium bromide, by mediating apparent H(+)-Na(+)-Cl(-) symport. Remarkably, LmrA activity significantly enhances survival of high-salt adapted lactococcal cells during ionic downshift.

CONCLUSIONS/SIGNIFICANCE

The observations on H(+)-Na(+)-Cl(-) co-transport substantiate earlier suggestions of H(+)-coupled transport by LmrA, and indicate a novel link between the activity of LmrA and salt stress. Our findings demonstrate the relevance of investigations into the bioenergetics of substrate translocation by ABC transporters for our understanding of fundamental mechanisms in this superfamily. This study represents the first use of electrophysiological techniques to analyze substrate transport by a purified multidrug transporter.

Similarities between ATP-dependent and ion-coupled multidrug transporters

The movement of drugs across biological membranes is mediated by two major classes of membrane transporters. Primary-active, ABC (ATP-binding cassette) multidrug transporters are dependent on ATP-binding/hydrolysis, whereas secondary-active multidrug transporters are coupled to the proton (or sodium)-motive force that exists across the plasma membrane. Recent work on LmrA, an ABC multidrug transporter in Lactococcus lactis, suggests that primary- and secondary-active multidrug transporters share functional and structural features. Some of these similarities and their implications for the mechanism of transport by ABC multidrug transporters will be discussed.

“The Art of Successful Publication” ECCO 13 Workshop Report

Having your work published in a good journal is the life-blood of research. Publications are the key element in scientific communication and influence future funding and cancer development for the authors. Every year more and more manuscripts are submitted and competition for acceptance is fierce. The editors of EJC recently held a workshop to discuss ways to improve manuscript writing, and this paper summarises their recommendations. Choose a title carefully, keep the introduction short, avoid confusing methods with results, and use figures wherever possible. Discuss only the relevance of new findings to published literature. Above all read the specific "instructions to authors" -- it is surprising how often this is ignored -- at peril!

Drug-lipid A interactions on the Escherichia coli ABC transporter MsbA

MsbA is an essential ATP-binding cassette half-transporter in the cytoplasmic membrane of the gram-negative Escherichia coli and is required for the export of lipopolysaccharides (LPS) to the outer membrane, most likely by transporting the lipid A core moiety. Consistent with the homology of MsbA to the multidrug transporter LmrA in the gram-positive Lactococcus lactis, our recent work in E. coli suggested that MsbA might interact with multiple drugs. To enable a more detailed analysis of multidrug transport by MsbA in an environment deficient in LPS, we functionally expressed MsbA in L. lactis. MsbA expression conferred an 86-fold increase in resistance to the macrolide erythromycin. A kinetic characterization of MsbA-mediated ethidium and Hoechst 33342 transport revealed apparent single-site kinetics and competitive inhibition of these transport reactions by vinblastine with K(i) values of 16 and 11 microM, respectively. We also detected a simple noncompetitive inhibition of Hoechst 33342 transport by free lipid A with a K(i) of 57 microM, in a similar range as the K(i) for vinblastine, underscoring the relevance of our LPS-less lactococcal model for studies on MsbA-mediated drug transport. These observations demonstrate the ability of heterologously expressed MsbA to interact with free lipid A and multiple drugs in the absence of auxiliary E. coli proteins. Our transport data provide further functional support for direct LPS-MsbA interactions as observed in a recent crystal structure for MsbA from Salmonella enterica serovar Typhimurium (C. L. Reyes and G. Chang, Science 308:1028-1031, 2005).

A critical role of a carboxylate in proton conduction by the ATP-binding cassette multidrug transporter LmrA

The ATP binding cassette (ABC) transporter LmrA from the bacterium Lactococcus lactis is a homolog of the human multidrug resistance P-glycoprotein (ABCB1), the activity of which impairs the efficacy of chemotherapy. In a previous study, LmrA was shown to mediate ethidium efflux by an ATP-dependent proton-ethidium symport reaction in which the carboxylate E314 is critical. The functional importance of this key residue for ABC proteins was suggested by its conservation in a wider family of related transporters; however, the structural basis of its role was not apparent. Here, we have used homology modeling to define the structural environment of E314. The residue is nested in a hydrophobic environment that probably elevates its pKa, accounting for the pH dependency of drug efflux that we report in this work. Functional analyses of wild-type and mutant proteins in cells and proteoliposomes support our proposal for the mechanistic role of E314 in proton-coupled ethidium transport. As the carboxylate is known to participate in proton translocation by secondary-active transporters, our observations suggest that this substituent can play a similar role in the activity of ABC transporters.

Arginine-482 is not essential for transport of antibiotics, primary bile acids and unconjugated sterols by the human breast cancer resistance protein (ABCG2)

The human BCRP (breast cancer resistance protein, also known as ABCG2) is an ABC (ATP-binding cassette) transporter that extrudes various anticancer drugs from cells, causing multidrug resistance. To study the molecular determinants of drug specificity of BCRP in more detail, we have expressed wild-type BCRP (BCRP-R) and the drug-selected cancer cell line-associated R482G (Arg482-->Gly) mutant BCRP (BCRP-G) in Lactococcus lactis. Drug resistance and the rate of drug efflux in BCRP-expressing cells were proportional to the expression level of the protein and affected by the R482G mutation, pointing to a direct role of BCRP in drug transport in L. lactis. In agreement with observations in mammalian cells, the BCRP-R-mediated transport of the cationic substrates rhodamine 123 and tetramethylrosamine was significantly decreased compared with the activity of BCRP-G. In addition, BCRP-R showed an enhanced interaction with the anionic anticancer drug methotrexate when compared with BCRP-G, suggesting that structure/substrate specificity relationships in BCRP, as observed in eukaryotic expression systems, are maintained in prokaryotic L. lactis. Interestingly, BCRP-R exhibited a previously unestablished ability to transport antibiotics, unconjugated sterols and primary bile acids in L. lactis, for which the R482G mutation was not critical. Since Arg482 is predicted to be present in the intracellular domain of BCRP, close to transmembrane segment 3, our results point to a role of this residue in electrostatic interactions with charged substrates including rhodamine 123 and methotrexate. Since unconjugated sterols are neutral molecules and bile acids and many antibiotics are engaged in protonation/deprotonation equilibria at physiological pH, our observations may point either to a lack of interaction between Arg482 and neutral or neutralized moieties in these substrates during transport or to the interaction of these substrates with regions in BCRP not including Arg482.

Investigation of the Booroola (FecB) and Inverdale (FecX(I)) mutations in 21 prolific breeds and strains of sheep sampled in 13 countries

Twenty-one of the world's prolific sheep breeds and strains were tested for the presence of the FecB mutation of BMPR1B and the FecX(I) mutation of BMP15. The breeds studied were Romanov (2 strains), Finn (2 strains), East Friesian, Teeswater, Blueface Leicester, Hu, Han, D'Man, Chios, Mountain Sheep (three breeds), German Whiteheaded Mutton, Lleyn, Loa, Galician, Barbados Blackbelly (pure and crossbred) and St. Croix. The FecB mutation was found in two breeds, Hu and Han from China, but not in any of the other breeds. The 12 Hu sheep sampled were all homozygous carriers of FecB (FecB(B)/FecB(B)) whereas the sample of 12 Han sheep included all three genotypes (FecB(B)/FecB(B), FecB(B)/FecB+, FecB+/FecB+) at frequencies of 0.33, 0.58 and 0.08, respectively. There was no evidence of FecX(I) in any of the breeds sampled.

An ABC transporter with a secondary-active multidrug translocator domain

Multidrug resistance, by which cells become resistant to multiple unrelated pharmaceuticals, is due to the extrusion of drugs from the cell's interior by active transporters such as the human multidrug resistance P-glycoprotein. Two major classes of transporters mediate this extrusion. Primary-active transporters are dependent on ATP hydrolysis, whereas secondary-active transporters are driven by electrochemical ion gradients that exist across the plasma membrane. The ATP-binding cassette (ABC) transporter LmrA is a primary drug transporter in Lactococcus lactis that can functionally substitute for P-glycoprotein in lung fibroblast cells. Here we have engineered a truncated LmrA protein that lacks the ATP-binding domain. Surprisingly, this truncated protein mediates a proton-ethidium symport reaction without the requirement for ATP. In other words, it functions as a secondary-active multidrug uptake system. These findings suggest that the evolutionary precursor of LmrA was a secondary-active substrate translocator that acquired an ATP-binding domain to enable primary-active multidrug efflux in L. lactis.

Reversible transport by the ATP-binding cassette multidrug export pump LmrA: ATP synthesis at the expense of downhill ethidium uptake

The ATP dependence of ATP-binding cassette (ABC) transporters has led to the widespread acceptance that these systems are unidirectional. Interestingly, in the presence of an inwardly directed ethidium concentration gradient in ATP-depleted cells of Lactococcus lactis, the ABC multidrug transporter LmrA mediated the reverse transport (or uptake) of ethidium with an apparent K(t) of 2.0 microm. This uptake reaction was competitively inhibited by the LmrA substrate vinblastine and was significantly reduced by an E314A substitution in the membrane domain of the transporter. Similar to efflux, LmrA-mediated ethidium uptake was inhibited by the E512Q replacement in the Walker B region of the nucleotide-binding domain of the protein, which strongly reduced its drug-stimulated ATPase activity, consistent with published observations for other ABC transporters. The notion that ethidium uptake is coupled to the catalytic cycle in LmrA was further corroborated by studies in LmrA-containing cells and proteoliposomes in which reverse transport of ethidium was associated with the net synthesis of ATP. Taken together, these data demonstrate that the conformational changes required for drug transport by LmrA are (i) not too far from equilibrium under ATP-depleted conditions to be reversed by appropriate changes in ligand concentrations and (ii) not necessarily coupled to ATP hydrolysis, but associated with a reversible catalytic cycle. These findings and their thermodynamic implications shed new light on the mechanism of energy coupling in ABC transporters and have implications for the development of new modulators that could enable reverse transport-associated drug delivery in cells through their ability to uncouple ATP binding/hydrolysis from multidrug efflux.

Usefulness of cytological specimens from bronchial brushings and bronchial washings in addition to endobronchial biopsies during bronchoscopy for lung cancer: 3 years data from a chest clinic in a general hospital

A retrospective review of all bronchoscopy cases for investigation of lung cancer between January 1997 and December 1999 was done. The cases were included if endobronchial mass was visible (Group A) or when there was an abnormal mucosa and/or bronchial narrowing in the absence of a mass (Group B). All patients in Group A (n = 177) underwent endobronchial biopsy (EB) bronchial brushings (BB) and bronchial washings (BW). All cases in Group B underwent transbronchial biopsy (TBB), BB and BW. Only a small increase in the positive results for cancer was seen when cytology specimens (BB and BW) were added to EB (85.3% vs 88.1%, McNemar's P = 0.06) in Group A but there was a significant increase in Group B (37.3% vs 54.2%. McNemar's, P = 0.001). Therefore although cytology specimens did not significantly add to overall yield of positive results when endobronchial lesions were visible, when mass lesions were not visible, cytology specimens increased the yield by 16.9%.

The ATP binding cassette multidrug transporter LmrA and lipid transporter MsbA have overlapping substrate specificities

LmrA is an ATP binding cassette (ABC) multidrug transporter in Lactococcus lactis that is a structural and functional homologue of the human multidrug resistance P-glycoprotein MDR1 (ABCB1). LmrA is also homologous to MsbA, an essential ABC transporter in Escherichia coli involved in the trafficking of lipids, including Lipid A. We have compared the substrate specificities of LmrA and MsbA in detail. Surprisingly, LmrA was able to functionally substitute for a temperature-sensitive mutant MsbA in E. coli WD2 at non-permissive temperatures, suggesting that LmrA could transport Lipid A. LmrA also exhibited a Lipid A-stimulated, vanadate-sensitive ATPase activity. Reciprocally, the expression of MsbA conferred multidrug resistance on E. coli. Similar to LmrA, MsbA interacted with photoactivatable substrate [3H]azidopine, displayed a daunomycin, vinblastine, and Hoechst 33342-stimulated vanadate-sensitive ATPase activity, and mediated the transport of ethidium from cells and Hoechst 33342 in proteoliposomes containing purified and functionally reconstituted protein. Taken together, these data demonstrate that MsbA and LmrA have overlapping substrate specificities. Our observations imply the presence of structural elements in the recently published crystal structures of MsbA in E. coli and Vibrio cholera (Chang, G., and Roth, C. B. (2001) Science 293, 1793-1800; Chang, G. (2003) J. Mol. Biol. 330, 419-430) that support drug-protein interactions and suggest a possible role for LmrA in lipid trafficking in L. lactis.

A new dimer interface for an ABC transporter

The crystallization of MsbA, an ATP-binding cassette (ABC) transporter involved in the transport of Lipid A in Escherichia coli, provided a fascinating glimpse into the high-resolution structure of an ABC transporter at 4.8 A. The E. coli crystal structure of MsbA reveals a dimer. Although the structure of the MsbA monomer is consistent with the biochemistry of ABC transporters, including the human multidrug resistance P-glycoprotein, the interface between the monomers in the MsbA dimer may not reflect the biologically relevant interface. We considered the interface in a two-armed MsbA dimer, named spiral. Our findings indicate that (i) the spiral MsbA dimer may have biological relevance for ABC transporters that interact with lipophilic substrates, and (ii) the dimer interface observed in the crystal structure of E. coli MsbA represents a crystallization artefact. A comparison of the spiral MsbA dimer with the recently published structure of MsbA in Vibrio cholera is also described.

Sterol transport by the human breast cancer resistance protein (ABCG2) expressed in Lactococcus lactis

The human breast cancer resistance protein (BCRP, also know as ABCG2, MXR, or ABCP) is one of the more recently discovered ATP-binding cassette (ABC) transporters that confer resistance on cancer cells by mediating multidrug efflux. In the present study, we have obtained functional expression of human BCRP in the Gram-positive bacterium Lactococcus lactis. BCRP expression conferred multidrug resistance on the lactococcal cells, which was based on ATP-dependent drug extrusion. BCRP-mediated ATPase and drug transport activities were inhibited by the BCRP-specific modulator fumitremorgin C. To our knowledge these data represent the first example of the functional expression of a mammalian ABC half-transporter in bacteria. Although members of the ABCG subfamily (such as ABCG1 and ABCG5/8) have been implicated in the transport of sterols, such a role has not yet been established for BCRP. Interestingly, the BCRP-associated ATPase activity in L. lactis was significantly stimulated by (i) sterols including cholesterol and estradiol, (ii) natural steroids such as progesterone and testosterone, and (iii) the anti-estrogen anticancer drug tamoxifen. In addition, BCRP mediated the efflux of [3H]estradiol from lactococcal cells. Our findings suggest that BCRP may play a role in the transport of sterols in human, in addition to its ability to transport multiple drugs and toxins.

Substrate-triggered recruitment of the TolC channel-tunnel during type I export of hemolysin by Escherichia coli

A defining event in type I export of hemolysin by Escherichia coli is the substrate-triggered recruitment of the TolC channel-tunnel by an inner membrane complex. This complex comprises a traffic ATPase (HlyB) and the 478 residue adaptor protein (HlyD), which contacts TolC during recruitment. HlyD has a large periplasmic domain (amino acid residues 81-478) linked by a single transmembrane helix to a small N-terminal cytosolic domain (1-59). Export was disabled by deletion of the ca 60 amino acid residue cytosolic domain of HlyD, even though the truncated HlyD (HlyDDelta45) was, like the wild-type, able to trimerise in the cytosolic membrane, and interact with the traffic ATPase. The mutant HlyB/HlyDDelta45 inner membrane complex engaged the hemolysin substrate, but this substrate-engaged complex failed to trigger recruitment of TolC. Further analyses showed that HlyDDelta45 was specifically unable to bind the substrate. The result suggests that substrate engagement by the traffic ATPase alone is insufficient to trigger TolC recruitment, and that substrate binding to the HlyD cytosolic domain is essential. Analysis of three further N-terminal deletion variants, HlyDDelta26, HlyDDelta26-45 and HlyDDelta34-38, indicated that an extreme N-terminal amphipathic helix and a cytosolic cluster of charged residues are central to the cytosolic domain function. The cytosolic amphipathic helix was not essential for substrate engagement or TolC recruitment, but export was impaired without it. In contrast, when the charged amino acid residues were deleted, the substrate was still engaged by HlyD but engagement was unproductive, i.e. TolC recruitment was not triggered. Our results are compatible with the HlyD cytosolic domain mediating transduction of the substrate binding signal directly, presumably to the HlyD periplasmic domain, to trigger recruitment of TolC and assemble the type I export complex.