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1.  Phytochemicals increase the antibacterial activity of antibiotics by acting on a drug efflux pump 
MicrobiologyOpen  2014;3(6):885-896.
Drug efflux pumps confer resistance upon bacteria to a wide range of antibiotics from various classes. The expression of efflux pumps are also implicated in virulence and biofilm formation. Moreover, organisms can only acquire resistance in the presence of active drug efflux pumps. Therefore, efflux pump inhibitors (EPIs) are attractive compounds to reverse multidrug resistance and to prevent the development of resistance in clinically relevant bacterial pathogens. We investigated the potential of pure compounds isolated from plants to act as EPIs. In silico screening was used to predict the bioactivity of plant compounds and to compare that with the known EPI, phe-arg-β-naphthylamide (PAβN). Subsequently, promising products have been tested for their ability to inhibit efflux. Plumbagin nordihydroguaretic acid (NDGA) and to a lesser degree shikonin, acted as sensitizers of drug-resistant bacteria to currently used antibiotics and were able to inhibit the efflux pump-mediated removal of substrate from cells. We demonstrated the feasibility of in silico screening to identify compounds that potentiate the action of antibiotics against drug-resistant strains and which might be potentially useful lead compounds for an EPI discovery program.
PMCID: PMC4263512  PMID: 25224951
Antibiotic; efflux pump inhibitors; multidrug resistance; natural products
2.  Stimulation of Inositol 1,4,5-Trisphosphate (IP3) Receptor Subtypes by Analogues of IP3 
PLoS ONE  2013;8(1):e54877.
Most animal cells express mixtures of the three subtypes of inositol 1,4,5-trisphosphate receptor (IP3R) encoded by vertebrate genomes. Activation of each subtype by different agonists has not hitherto been examined in cells expressing defined homogenous populations of IP3R. Here we measure Ca2+ release evoked by synthetic analogues of IP3 using a Ca2+ indicator within the lumen of the endoplasmic reticulum of permeabilized DT40 cells stably expressing single subtypes of mammalian IP3R. Phosphorylation of (1,4,5)IP3 to (1,3,4,5)IP4 reduced potency by ∼100-fold. Relative to (1,4,5)IP3, the potencies of IP3 analogues modified at the 1-position (malachite green (1,4,5)IP3), 2-position (2-deoxy(1,4,5)IP3) or 3-position (3-deoxy(1,4,5)IP3, (1,3,4,5)IP4) were similar for each IP3R subtype. The potency of an analogue, (1,4,6)IP3, in which the orientations of the 2- and 3-hydroxyl groups were inverted, was also reduced similarly for all three IP3R subtypes. Most analogues of IP3 interact similarly with the three IP3R subtypes, but the decrease in potency accompanying removal of the 1-phosphate from (1,4,5)IP3 was least for IP3R3. Addition of a large chromophore (malachite green) to the 1-phosphate of (1,4,5)IP3 only modestly reduced potency suggesting that similar analogues could be used to measure (1,4,5)IP3 binding optically. These data provide the first structure-activity analyses of key IP3 analogues using homogenous populations of each mammalian IP3R subtype. They demonstrate broadly similar structure-activity relationships for all mammalian IP3R subtypes and establish the potential utility of (1,4,5)IP3 analogues with chromophores attached to the 1-position.
PMCID: PMC3556037  PMID: 23372785
3.  Activation of IP3 receptors requires an endogenous 1-8-14 calmodulin-binding motif 
Biochemical Journal  2012;449(Pt 1):39-49.
Binding of IP3 (inositol 1,4,5-trisphosphate) to the IP3-binding core (residues 224–604) of IP3Rs (IP3 receptors) initiates opening of these ubiquitous intracellular Ca2+ channels. The mechanisms are unresolved, but require conformational changes to pass through the suppressor domain (residues 1–223). A calmodulin-binding peptide derived from myosin light chain kinase uncouples these events. We identified a similar conserved 1-8-14 calmodulin-binding motif within the suppressor domain of IP3R1 and, using peptides and mutagenesis, we demonstrate that it is essential for IP3R activation, whether assessed by IP3-evoked Ca2+ release or patch-clamp recoding of nuclear IP3R. Mimetic peptides specifically inhibit activation of IP3R by uncoupling the IP3-binding core from the suppressor domain. Mutations of key hydrophobic residues within the endogenous 1-8-14 motif mimic the peptides. Our results show that an endogenous 1-8-14 motif mediates conformational changes that are essential for IP3R activation. The inhibitory effects of calmodulin and related proteins may result from disruption of this essential interaction.
PMCID: PMC3685217  PMID: 23009366
1-8-14 motif; calcium signalling; calmodulin; inositol 1,4,5-trisphosphate receptor; myosin light chain kinase (MLCK); BCR, B-cell receptor; CaBP1, Ca2+-binding protein 1; CaM, calmodulin; CLM, cytosol-like medium; IP3, inositol 1,4,5-trisphosphate; IBC, IP3-binding core; IP3R, IP3 receptor; MLCK, myosin light chain kinase; NT, N-terminus; RyR, ryanodine receptor; SD, suppressor domain
4.  In vitro Antiproliferative Activity of Benzopyranone Derivatives in Comparison with Standard Chemotherapeutic Drugs 
Archiv Der Pharmazie  2010;344(2):102-110.
The cytotoxic activities of five new benzopyranone derivatives containing basic amino side chain are described. Their cytotoxicities against ER (+) MCF-7 and ER (−) MDA-MB-231 human breast cancer cell lines, and Ishikawa human endometrial cell line were determined after 72 h drug exposure employing CellTiter-Glo assay at concentrations ranging from 0.01 – 1.0 × 105 nM. The antiproliferative activities of these compounds were compared to tamoxifen (TAM), 4-hydroxytamoxifen (4-OHT, active metabolite of tamoxifen) and raloxifene (RAL). In vitro results indicated that compounds 9, 10, 12 and 13 were more potent than TAM against the human breast cancer cell lines with IC50 < 20 µM. The in silico structure-activity relationships of these compounds and their binding mode within the estrogen receptor (ER) binding site using AutoDock vina are discussed.
PMCID: PMC3361755  PMID: 21290426
Coumarin; estrogen receptors; anticancer activity; antiproliferative agents; cytotoxic activity
5.  The endo-lysosomal system as an NAADP-sensitive acidic Ca2+ store: Role for the two-pore channels 
Cell calcium  2011;50(2):157-167.
Accumulating evidence suggests that the endo-lysosomal system provides a substantial store of Ca2+ that is tapped by the Ca2+-mobilizing messenger, NAADP. In this article, we review evidence that NAADP-mediated Ca2+ release from this acidic Ca2+ store proceeds through activation of the newly described two-pore channels (TPCs). We discuss recent advances in defining the sub-cellular targeting, topology and biophysics of TPCs. We also discuss physiological roles and the evolution of this ubiquitous ion channel family.
PMCID: PMC3160778  PMID: 21529939
NAADP; Two-pore channels; TPC1; TPC2; TPCN1; TPCN2; Calcium; Endosomes; Lysosomes; Acidic calcium stores
6.  Ca2+ Channels on the Move 
Biochemistry  2010;49(24):5082.
PMCID: PMC3048451
7.  An NAADP-gated Two-pore Channel Targeted to the Plasma Membrane Uncouples Triggering from Amplifying Ca2+ Signals* 
The Journal of Biological Chemistry  2010;285(49):38511-38516.
Nicotinic acid adenine dinucleotide phosphate (NAADP) is a ubiquitous messenger proposed to stimulate Ca2+ release from acidic organelles via two-pore channels (TPCs). It has been difficult to resolve this trigger event from its amplification via endoplasmic reticulum Ca2+ stores, fuelling speculation that archetypal intracellular Ca2+ channels are the primary targets of NAADP. Here, we redirect TPC2 from lysosomes to the plasma membrane and show that NAADP evokes Ca2+ influx independent of ryanodine receptors and that it activates a Ca2+-permeable channel whose conductance is reduced by mutation of a residue within a putative pore. We therefore uncouple TPC2 from amplification pathways and prove that it is a pore-forming subunit of an NAADP-gated Ca2+ channel.
PMCID: PMC2992283  PMID: 20880839
Biophysics; Calcium Channels; Calcium Intracellular Release; Lysosomes; Ryanodine; Trafficking; NAADP; Two-pore Channels
8.  Regulation of Inositol 1,4,5-Trisphosphate Receptors by cAMP Independent of cAMP-dependent Protein Kinase* 
The Journal of Biological Chemistry  2010;285(17):12979-12989.
In HEK cells stably expressing type 1 receptors for parathyroid hormone (PTH), PTH causes a sensitization of inositol 1,4,5-trisphosphate receptors (IP3R) to IP3 that is entirely mediated by cAMP and requires cAMP to pass directly from type 6 adenylyl cyclase (AC6) to IP3R2. Using DT40 cells expressing single subtypes of mammalian IP3R, we demonstrate that high concentrations of cAMP similarly sensitize all IP3R isoforms to IP3 by a mechanism that does not require cAMP-dependent protein kinase (PKA). IP3 binding to IP3R2 is unaffected by cAMP, and sensitization is not mediated by the site through which ATP potentiates responses to IP3. In single channel recordings from excised nuclear patches of cells expressing IP3R2, cAMP alone had no effect, but it increased the open probability of IP3R2 activated by a submaximal concentration of IP3 alone or in combination with a maximally effective concentration of ATP. These results establish that cAMP itself increases the sensitivity of all IP3R subtypes to IP3. For IP3R2, this sensitization results from cAMP binding to a novel site that increases the efficacy of IP3. Using stably expressed short hairpin RNA to reduce expression of the G-protein, Gαs, we demonstrate that attenuation of AC activity by loss of Gαs more substantially reduces sensitization of IP3R by PTH than does comparable direct inhibition of AC. This suggests that Gαs may also specifically associate with each AC·IP3R complex. We conclude that all three subtypes of IP3R are regulated by cAMP independent of PKA. In HEK cells, where IP3R2 selectively associates with AC6, Gαs also associates with the AC·IP3R signaling junction.
PMCID: PMC2857138  PMID: 20189985
Adenylate Cyclase (Adenylyl Cyclase); Calcium; Calcium Channels; Calcium Intracellular Release; Cyclic AMP (cAMP); Signal Transduction
9.  Ca2+ Channels on the Move† 
Biochemistry  2009;48(51):12062-12080.
The versatility of Ca2+ as an intracellular messenger derives largely from the spatial organization of cytosolic Ca2+ signals, most of which are generated by regulated openings of Ca2+-permeable channels. Most Ca2+ channels are expressed in the plasma membrane (PM). Others, including the almost ubiquitous inositol 1,4,5-trisphosphate receptors (IP3R) and their relatives, the ryanodine receptors (RyR), are predominantly expressed in membranes of the sarcoplasmic or endoplasmic reticulum (ER). Targeting of these channels to appropriate destinations underpins their ability to generate spatially organized Ca2+ signals. All Ca2+ channels begin life in the cytosol, and the vast majority are then functionally assembled in the ER, where they may either remain or be dispatched to other membranes. Here, by means of selective examples, we review two issues related to this trafficking of Ca2+ channels via the ER. How do cells avoid wayward activity of Ca2+ channels in transit as they pass from the ER via other membranes to their final destination? How and why do some cells express small numbers of the archetypal intracellular Ca2+ channels, IP3R and RyR, in the PM?
PMCID: PMC2797372  PMID: 19928968

Results 1-9 (9)