Engineering a Two-Component Hemostat for the Treatment of Internal Bleeding through Wound-Targeted Crosslinking.

Primary hemostasis (platelet plug formation) and secondary hemostasis (fibrin clot formation) are intertwined processes that occur upon vascular injury. Researchers have sought to target wounds by leveraging cues specific to these processes, such as using peptides that bind activated platelets or fibrin. While these materials have shown success in various injury models, they are commonly designed for the purpose of treating solely primary or secondary hemostasis. In this work, a two-component system consisting of a targeting component (azide/GRGDS PEG-PLGA nanoparticles) and a crosslinking component (multifunctional DBCO) is developed to treat internal bleeding. The system leverages increased injury accumulation to achieve crosslinking above a critical concentration, addressing both primary and secondary hemostasis by amplifying platelet recruitment and mitigating plasminolysis for greater clot stability. Nanoparticle aggregation is measured to validate concentration-dependent crosslinking, while a 1:3 azide/GRGDS ratio is found to increase platelet recruitment, decrease clot degradation in hemodiluted environments, and decrease complement activation. Finally, this approach significantly increases survival relative to the particle-only control in a liver resection model. In light of prior successes with the particle-only system, these results emphasize the potential of this technology in aiding hemostasis and the importance of a holistic approach in engineering new treatments for hemorrhage.

Hops compounds modulatory effects and 6-prenylnaringenin dual mode of action on GABAA receptors.

Hops (Humulus lupulus L.), a major component of beer, contain potentially neuroactive compounds that made it useful in traditional medicine as a sleeping aid. The present study aims to investigate the individual components in hops acting as allosteric modulators in GABAA receptors and bring further insight into the mode of action behind the sedative properties of hops. GABA-potentiating effects were measured using [3H]ethynylbicycloorthobenzoate (EBOB) radioligand binding assay in native GABAA receptors. Flumazenil sensitivity of GABA-potentiating effects, [3H]Ro 15-4513, and [3H]flunitrazepam binding assays were used to examine the binding to the classical benzodiazepines site. Humulone (alpha acid) and 6-prenylnaringenin (prenylflavonoid) were the most potent compounds displaying a modulatory activity at low micromolar concentrations. Humulone and 6-prenylnaringenin potentiated GABA-induced displacement of [3H]EBOB binding in a concentration-dependent manner where the IC50 values for this potentiation in native GABAA receptors were 3.2 µM and 3.7 µM, respectively. Flumazenil had no significant effects on humulone- or 6-prenylnaringenin-induced displacement of [3H]EBOB binding. [3H]Ro 15-4513 and [3H]flunitrazepam displacements were only minor with humulone but surprisingly prominent with 6-prenylnaringenin despite its flumazenil-insensitive modulatory activity. Thus, we applied molecular docking methods to investigate putative binding sites and poses of 6-prenylnaringenin at the GABAA receptor α1ß2γ2 isoform. Radioligand binding and docking results suggest a dual mode of action by 6-prenylnaringenin on GABAA receptors where it may act as a positive allosteric modulator at α+ß- binding interface as well as a null modulator at the flumazenil-sensitive α+γ2- binding interface.

Attenuation of dopamine-induced GABA release in problem gamblers.

INTRODUCTION: We have previously shown that an interaction between medial prefrontal and parietal cortices is instrumental in promoting self-awareness via synchronizing oscillations in the gamma range. The synchronization of these oscillations is modulated by dopamine release. Given that such oscillations result from intermittent GABA stimulation of pyramidal cells, it is of interest to determine whether the dopaminergic system regulates GABA release directly in cortical paralimbic regions. Here, we test the hypothesis that the regulation of the GABA-ergic system by the dopaminergic system becomes attenuated in problem gamblers resulting in addictive behaviors and impaired self-awareness. METHODS: [11 C]Ro15-4513 PET, a marker of benzodiazepine α1/α5 receptor availability in the GABA receptor complex, was used to detect changes in synaptic GABA levels after oral doses of 100mg L-dopa in a double-blind controlled study of male problem gamblers (N = 10) and age-matched healthy male controls (N = 10). RESULTS: The mean reduction of cortical gray matter GABA/BDZ receptor availability induced by L-dopa was significantly attenuated in the problem gambling group compared to the healthy control group (p = 0.0377). CONCLUSIONS: Our findings demonstrate that: (a) Exogenous dopamine can induce synaptic GABA release in healthy controls. (b) This release is attenuated in frontal cortical areas of males suffering from problem gambling, possibly contributing to their loss of inhibitory control. This suggests that dysfunctional dopamine regulation of GABA release may contribute to problem gambling and gambling disorder.

Quick Click: The DNA-Templated Ligation of 3'-O-Propargyl- and 5'-Azide-Modified Strands Is as Rapid as and More Selective than Ligase.

The copper(I)-mediated azide-alkyne cycloaddition (CuAAC) of 3'-propargyl ether and 5'-azide oligonucleotides is a particularly promising ligation system because it results in triazole linkages that effectively mimic the phosphate-sugar backbone of DNA, leading to unprecedented tolerance of the ligated strands by polymerases. However, for a chemical ligation strategy to be a viable alternative to enzymatic systems, it must be equally as rapid, as discriminating, and as easy to use. We found that the DNA-templated reaction with these modifications was rapid under aerobic conditions, with nearly quantitative conversion in 5 min, resulting in a kobs value of 1.1 min-1 , comparable with that measured in an enzymatic ligation system by using the highest commercially available concentration of T4 DNA ligase. Moreover, the CuAAC reaction also exhibited greater selectivity in discriminating C:A or C:T mismatches from the C:G match than that of T4 DNA ligase at 29 °C; a temperature slightly below the perfect nicked duplex dissociation temperature, but above that of the mismatched duplexes. These results suggest that the CuAAC reaction of 3'-propargyl ether and 5'-azide-terminated oligonucleotides represents a complementary alternative to T4 DNA ligase, with similar reaction rates, ease of setup and even enhanced selectivity for certain mismatches.

Inhibitor mechanisms in the S1 binding site of the dopamine transporter defined by multi-site molecular tethering of photoactive cocaine analogs.

Dopamine transporter (DAT) blockers like cocaine and many other abused and therapeutic drugs bind and stabilize an inactive form of the transporter inhibiting reuptake of extracellular dopamine (DA). The resulting increases in DA lead to the ability of these drugs to induce psychomotor alterations and addiction, but paradoxical findings in animal models indicate that not all DAT antagonists induce cocaine-like behavioral outcomes. How this occurs is not known, but one possibility is that uptake inhibitors may bind at multiple locations or in different poses to stabilize distinct conformational transporter states associated with differential neurochemical endpoints. Understanding the molecular mechanisms governing the pharmacological inhibition of DAT is therefore key for understanding the requisite interactions for behavioral modulation and addiction. Previously, we leveraged complementary computational docking, mutagenesis, peptide mapping, and substituted cysteine accessibility strategies to identify the specific adduction site and binding pose for the crosslinkable, photoactive cocaine analog, RTI 82, which contains a photoactive azide attached at the 2ß position of the tropane pharmacophore. Here, we utilize similar methodology with a different cocaine analog N-[4-(4-azido-3-I-iodophenyl)-butyl]-2-carbomethoxy-3-(4-chlorophenyl)tropane, MFZ 2-24, where the photoactive azide is attached to the tropane nitrogen. In contrast to RTI 82, which crosslinked into residue Phe319 of transmembrane domain (TM) 6, our findings show that MFZ 2-24 adducts to Leu80 in TM1 with modeling and biochemical data indicating that MFZ 2-24, like RTI 82, occupies the central S1 binding pocket with the (+)-charged tropane ring nitrogen coordinating with the (-)-charged carboxyl side chain of Asp79. The superimposition of the tropane ring in the three-dimensional binding poses of these two distinct ligands provides strong experimental evidence for cocaine binding to DAT in the S1 site and the importance of the tropane moiety in competitive mechanisms of DA uptake inhibition. These findings set a structure-function baseline for comparison of typical and atypical DAT inhibitors and how their interactions with DAT could lead to the loss of cocaine-like behaviors.

Subunit-directed click coupling via doubly cross-linked hemoglobin efficiently produces readily purified functional bis-tetrameric oxygen carriers.

While cross-linked hemoglobin (Hb) tetramers can deliver oxygen as a supplement to red cells, they also cause unacceptable increases in blood pressure, presumably from their penetration of the linings of blood vessels (endothelia) where the internal hemes bind endogenous nitric oxide (NO). This penetration would lower the local concentration of NO that normally induces vasodilation. Enlarging the effective size of the oxygen-carrying protein by coupling two Hbs can prevent their extravasation. Efficient and selective protein-protein coupling to produce those species has been a significant challenge. Introduction of an azide within a protein provides a directionally-oriented reaction site for utilization of the Cu(i)-catalyzed azide-alkyne cycloaddition (CuAAC) in the protein-protein-coupling process based on solubility-directed sequential addition to a bis-alkyne. However, it is known that Hb with an azide-containing cross-link between α-subunits is unreactive in CuAAC. To direct reaction away from the α-subunits of Hb, a specific fumaryl cross-link is installed exclusively between the most reactive sites on those subunits, thereby blocking the α-99 lysyl groups and preventing any further reaction. This modification allows installation of an azide-containing cross-link exclusively between lysine-82 ε-amino groups of the ß-subunits of Hb. The multiply interconnected sites establish a geometry that permits initial interfacial interaction of the cross-linked Hb-azide with Cu(i) and a bis-alkyne. After coupling, the protein-linked azide product undergoes CuAAC at the remaining alkyne with a second cross-linked Hb-azide, producing a fully functional cross-linked Hb bis-tetramer whose oxygenation and structural properties include cooperativity and oxygen affinity that should be suitable for testing as an alternative to red cells in transfusions.

Preclinical assessment of carboplatin treatment efficacy in lung cancer by 18F-ICMT-11-positron emission tomography.

Tumour response to therapy is assessed primarily in the clinic by monitoring reductions in tumour size. However, this approach lacks sensitivity since in many cases several weeks may elapse before there is evidence of tumour shrinkage. There is therefore a need to develop non-invasive imaging techniques for monitoring tumour treatment response in the clinic. Here, we assessed the pre-clinical utility of (18)F-ICMT-11 positron emission tomography--a method for detecting caspase 3/7 activation--in non-small cell lung cancer (NSCLC). (18)F-ICMT-11 uptake was compared to molecular biochemical measures of cell death in PC9 and A549 NSCLC cells following treatment with carboplatin in vitro and in vivo. Carboplatin-induced apoptosis in the ERCC1 low/mutant EGFR PC9 cells was characterised by time and dose-related increased caspase-3/7 activation, poly-ADP-ribose polymerase cleavage and Annexin V staining. 18F-ICMT-11 uptake was consequently increased up to 14-fold at 200 µM carboplatin compared to vehicle treated cells (P<0.01). In contrast, necrosis was the predominant death mechanism in ERCC1 high/wt EGFR A549 cells and no change in (18)F-ICMT-11 uptake was detected. In vivo, histological analysis of PC9 tumour xenografts indicated high pre-therapy necrosis. A 4.6-fold increase in cleaved caspase-3/7 was measured in non-necrotic regions of PC9 tumours at 48 h post carboplatin therapy. Average PET-derived tumour (18)F-ICMT-11 uptake was insensitive to changes in apoptosis in the presence of substantial pre-existing necrosis. PET-based voxel intensity sorting however, identified intra-tumoural regions of high (18)F-ICMT-11 uptake, enabling accurate assessment of apoptosis and therefore therapy response. In A549 tumours that lacked high pre-therapy necrosis, carboplatin induced growth inhibition that was only minimally associated with apoptosis and thus not detectable by (18)F-ICMT-11 PET.

Viable quantitative PCR for assessing the response of Candida albicans to antifungal treatment.

Propidium monoazide (PMA) or ethidium bromide monoazide (EMA) treatment has been used before nucleic acid detection methods, such as PCR, to distinguish between live and dead cells using membrane integrity as viability criterion. The performance of these DNA intercalating dyes was compared in many studies utilizing different microorganisms. These studies demonstrated that EMA and PMA differ in their abilities to identify nonviable cells from mixed cell populations, depending on the microorganism and the nature of the sample. Due to this heterogeneity, both dyes were used in the present study to specifically distinguish dead from live Candida albicans cells using viable quantitative PCR (qPCR). The viable qPCR was optimized, and the best results were obtained when pre-treating the cells for 10 min in the dark with 25 µM EMA followed by continuous photoactivation for 15 min. The suitability of this technique to distinguish clotrimazole- and fluconazole-treated C. albicans cells from untreated cells was then assessed. Furthermore, the antifungal properties of two commercial essential oils (Thymus vulgaris and Matricaria chamomilla) were evaluated. The viable qPCR method was determined to be a feasible technique for assessing the viability of C. albicans after drug treatment and may help to provide a rapid diagnostic and susceptibility testing method for fungal infections, especially for patients treated with antifungal therapies.

Biochemical mechanism of modulation of human P-glycoprotein (ABCB1) by curcumin I, II, and III purified from Turmeric powder.

P-glycoprotein (Pgp, ABCB1) is an ATP-dependent drug efflux pump linked to development of multidrug resistance (MDR) in cancer cells. Previously [Biochem Pharmacol 2002;64:573-82], we reported that a curcumin mixture could modulate both function and expression of Pgp. This study focuses on the effect of three major curcuminoids--curcumin I, II and III purified from a curcumin mixture--on modulation of Pgp function in a multidrug resistant human cervical carcinoma cell line (KB-V1). The similar IC(50) values for cytotoxicity of curcuminoids of KB-V1, and KB-3-1 (parental drug sensitive cell line) suggest that these curcuminoids may not be substrates for Pgp. Treating the cells with non-toxic doses of curcuminoids increased their sensitivity to vinblastine only in the Pgp expressing drug resistant cell line, KB-V1, and curcumin I retained the drug in KB-V1 cells more effectively than curcumin II and III, respectively. Effects of each curcuminoid on rhodamine123, calcein-AM, and bodipy-FL-vinblastine accumulation confirmed these findings. Curcumin I, II and III increased the accumulation of fluorescent substrates in a dose-dependent manner, and at 15 microM, curcumin I was the most effective. The inhibitory effect in a concentration-dependent manner of curcuminoids on verapamil-stimulated ATPase activity and photoaffinity labeling of Pgp with the [(125)I]-iodoarylazidoprazosin offered additional support; curcumin I was the most potent modulator. Taken together, these results indicate that curcumin I is the most effective MDR modulator among curcuminoids, and may be used in combination with conventional chemotherapeutic drugs to reverse MDR in cancer cells.

Template-dependent incorporation of 8-N3AMP into RNA with bacteriophage T7 RNA polymerase.

UV-induced photochemical crosslinking is a powerful approach that can be used for the identification of specific interactions involving nucleic acid-protein and nucleic acid-nucleic acid complexes. 8-AzidoATP (8-N(3)ATP) is a photoaffinity-labeling agent which has been widely used to elucidate the ATP binding site of a variety of proteins. However, its true potential as a photoactivatable nucleotide analog could not be exploited due to the lack of 8-azidoadenosine phosphoramidite, a monomer used in the synthesis of RNA, and the inability of 8-N(3)ATP to serve as an efficient substrate for bacteriophage RNA polymerase. In this study, we explored the ability of SP6, T3, and T7 RNA polymerases and metal ion cofactors to catalyze the incorporation of 8-N(3)AMP into RNA. Whereas transcription buffer containing 2.0-2.5 mM Mn(2+) supports T7 RNA polymerase-mediated insertion of 8-N(3)AMP into RNA, a mixture of 2.5 mM Mn(2+) and 2.5 mM Mg(2+) further improves the yield of 8-N(3)AMP-containing transcript. In addition, both RNA transcription and reverse transcription proceed with high fidelity for the incorporation of 8-N(3)AMP and complementary residue, respectively. Finally, we show that a high-affinity MS2 coat protein binding sequence, in which adenosine residues were replaced by 8-azidoadenosine, crosslinks to the coat protein of the Escherichia coli phage MS2.

Dopamine D4 receptor exon III genotype influence on the auditory evoked novelty P3.

The functional implications of the dopamine D4 receptor gene (DRD4) exon III polymorphism and its role in the modulation of temperament and in the pathophysiology of psychiatric disorders are still a matter of debate. Based on evidence from animal studies, we hypothesised that this polymorphism is involved in the modulation of the cortical response to novelty as reflected by the auditory evoked novelty P3 event-related potential. In a sample of 46 healthy volunteers, we observed an interactive effect of DRD4 exon III genotype and the eye-blink rate, a measure of central dopaminergic activity, on the novelty P3. These findings suggest that the DRD4 exon III polymorphism influences the processing of novelty and that this influence depends on tonic dopaminergic activity.

Second-sphere contributions to substrate-analogue binding in iron(III) superoxide dismutase.

A combination of spectroscopic and computational methods has been employed to explore the nature of the yellow and pink low-temperature azide adducts of iron(III) superoxide dismutase (N(3)-FeSOD), which have been known for more than two decades. Variable-temperature variable-field magnetic circular dichroism (MCD) data suggest that both species possess similar ferric centers with a single azide ligand bound, contradicting previous proposals invoking two azide ligands in the pink form. Complementary data obtained on the azide complex of the Q69E FeSOD mutant reveal that relatively minor perturbations in the metal-center environment are sufficient to produce significant spectral changes; the Q69E N(3)-FeSOD species is red in color at all temperatures. Resonance Raman (RR) spectra of the wild-type and Q69E mutant N(3)-FeSOD complexes are consistent with similar Fe-N(3) units in all three species; however, variations in energies and relative intensities of the RR features associated with this unit reveal subtle differences in (N(3)(-))-Fe(3+) bonding. To understand these differences on a quantitative level, density functional theory and semiempirical INDO/S-CI calculations have been performed on N(3)-FeSOD models. These computations support our model that a single azide ligand is present in all three N(3)-FeSOD adducts and suggest that their different appearances reflect differences in the Fe-N-N bond angle. A 10 degrees increase in the Fe-N-N bond angle is sufficient to account for the spectral differences between the yellow and pink wild-type N(3)-FeSOD species. We show that this bond angle is strongly affected by the second coordination sphere, which therefore might also play an important role in orienting incoming substrate for reaction with the FeSOD active site.

Characterization of gamma-aminobutyrate type A receptors with atypical coupling between agonist and convulsant binding sites in discrete brain regions.

Gamma-ainobutyric acid type A (GABA(A)) receptor ionophore ligand t-[35S]butylbicyclophosphorothionate ([35S]TBPS) was used in an autoradiographic assay on brain cryostat sections to visualize and characterize atypical GABA-insensitive [35S]TBPS binding previously described in certain recombinant GABA(A) receptors and the cerebellar granule cell layer. Picrotoxinin-sensitive but 1-mM GABA-insensitive [35S]TBPS binding was present in the rat cerebellar granule cell layer, many thalamic nuclei, subiculum and the internal rim of the cerebral cortex, amounting in these regions up to 6% of the basal binding determined in the absence of exogenous GABA. Similar binding properties were detected also in human and chicken brain sections. Like the GABA-sensitive [35S]TBPS binding, GABA-insensitive binding was profoundly decreased by pentobarbital, pregnanolone, loreclezole and Mg2+. The binding was reversible and apparently dependent on Cl- ions. Localization of the GABA-insensitive [35S]TBPS binding was not identical to that of high-affinity [3H]muscimol binding and diazepam-insensitive [3H]Ro 15-4513 binding, two previously established receptor subtype-dependent binding heterogeneities in the rat brain. The present study reveals a component of the GABA-ionophore enriched in the thalamus and cerebellar granule cells, possibly representing poorly desensitized or desensitizing receptors.

Reversal of P-glycoprotein and multidrug-resistance protein-mediated drug resistance in KB cells by 5-O-benzoylated taxinine K.

A newly synthesized taxoid originally from the Japanese yew Taxus cuspidata, 5-O-benzoylated taxinine K (BTK) was examined for its ability to reverse P-glycoprotein (P-gp) and multidrug resistance protein (MRP)-mediated multidrug resistance. BTK reversed the resistance to paclitaxel, doxorubicin (ADM), and vincristine (VCR) of KB-8-5 and KB-C2 cells that overexpress P-gp by directly interacting with P-gp. BTK also moderately reversed the resistance to ADM of KB/MRP cells that overexpress MRP. However, BTK neither inhibited the transporting activity of MRP nor reduced intracellular glutathione levels in KB/MRP cells. BTK shifted the distribution of ADM in KB/MRP cells from punctate cytoplasmic compartments to the nucleoplasm and cytoplasm by inhibiting acidification of cytoplasmic organelles. These two functions of BTK make it able to reverse both P-gp- and MRP-mediated MDR. BTK in combination with ADM should be useful for treating patients with tumors that overexpress both P-gp and MRP.

Evidence for a requirement for ATP hydrolysis at two distinct steps during a single turnover of the catalytic cycle of human P-glycoprotein.

P-glycoprotein (Pgp) is an ATP-dependent hydrophobic natural product anticancer drug efflux pump whose overexpression confers multidrug resistance to tumor cells. The work reported here deals with the elucidation of the energy requirement for substrate interaction with Pgp during the catalytic cycle. We show that the K(d) (412 nM) of the substrate analogue [(125)I]iodoarylazidoprazoin for Pgp is not altered by the presence of the nonhydrolyzable nucleotide 5'-adenylylimididiphosphate and vanadate (K(d) = 403 nM). Though binding of nucleotide per se does not affect interactions with the substrate, ATP hydrolysis results in a dramatic conformational change where the affinity of [(125)I]iodoarylazidoprazoin for Pgp trapped in transition-state conformation (Pgp x ADP x vanadate) is reduced >30-fold. To transform Pgp from this intermediate state of low affinity for substrate to the next catalytic cycle, i.e., a conformation that binds substrate with high affinity, requires conditions that permit ATP hydrolysis. Additionally, there is an inverse correlation (R(2) = 0.96) between 8AzidoADP (or ADP) release and the recovery of substrate binding. These results suggest that the release of nucleotide is necessary for reactivation but not sufficient. The hydrolysis of additional molecule(s) of ATP (or 8AzidoATP) is obligatory for the catalytic cycle to advance to completion. These data are consistent with the observed stoichiometry of two ATP molecules hydrolyzed for the transport of every substrate molecule. Our data demonstrate two distinct roles for ATP hydrolysis in a single turnover of the catalytic cycle of Pgp, one in the transport of substrate and the other in effecting conformational changes to reset the pump for the next catalytic cycle.

Photoaffinity labeling of DNA polymerase from Thermus thermophilus and DNA template by photoreactive analogs of dCTP.

Substrate properties of dCTP analogs N4-[2-(4-azidotetrafluorobenzoylamino)-ethyl]-2;-deoxycytidine-5; -triphosphate (FABdCTP), 5-[N-(4-azidotetrafluorobenzoyl)-3-amino-trans-propen-1-yl] -2;-deoxycytidine-5;-triphosphate (AlFABdCTP), and N4-[2-(2-nitro-5-azidobenzoylamino)-ethyl]-2;-deoxycytidine-5; -triphosphate (NABdCTP) were studied in the reaction of DNA synthesis catalyzed by DNA polymerase from the extremely thermophilic bacterium Thermus thermophilus B 35 (Tte DNA polymerase). The enzyme was photoaffinity labeled with the mentioned derivatives, NABdCTP being used for the first time. The photoreactive primers containing FABdCTP and AlFABdCTP were synthesized in situ by Tte DNA polymerase and used in the complementary addressed labeling of DNA template. The efficiency of DNA template labeling is shown to be a function of the structure of the photoactive group.

Analysis of random recombination between human MDR1 and mouse mdr1a cDNA in a pHaMDR-dihydrofolate reductase bicistronic expression system.

Human P-glycoprotein (Pgp) confers multidrug resistance (MDR) to otherwise sensitive cells. The homologous mouse Pgps, which are encoded by mouse mdr1a (also known as mdr3) and mdr1b (also known as mdr1), confer different degrees of resistance to the same MDR drugs and inhibitors. To create recombinants for the study of sequences responsible for these differences in drug-resistance, chimeric cDNA libraries can be constructed by homologous recombination of pools of related sequences. This mutagenesis approach is called DNA shuffling. To select for chimeric Pgp with an altered resistance profile, DNA shuffling between the homologous but not identical drug interacting transmembrane domains 5 and 6 of human MDR1 and mouse mdr1a was used. The chimeric proteins were expressed in human KB-3-1 cells. One recombinant Pgp (clone 3-4) with a novel phenotype was analyzed in detail. Inhibitors of Pgp, including verapamil and cyclosporin A, were less effective in reversing resistance of the chimeric Pgp compared with wild-type Pgp, for certain drugs. However, [125I]iodoarylazidoprazosin photoaffinity labeling of the chimeric Pgp and its binding competition with cyclosporin A, showed that cyclosporin A competed for the photoaffinity labeling. The chimeric Pgp cells stained less well with human-specific anti-Pgp mAb MRK16 than wild-type Pgp, despite having the described epitopes for MRK16. Staining with human-specific mAb UIC2 was increased when the chimeric protein was compared with wild-type Pgp. These results suggest an alteration in exposure of human Pgp specific epitopes in this chimeric Pgp, as well as a change in the interaction of reversing agents with the chimeric protein.

Substitution of alanine for serine 250 in the murine fatty acid transport protein inhibits long chain fatty acid transport.

The murine fatty acid transport protein (FATP) was identified on the basis of its ability to facilitate uptake of long chain fatty acids (LCFAs) when expressed in mammalian cells. To delineate FATP domains important for transport function, we cloned the human heart FATP ortholog. Comparison of the human, murine, and yeast amino acid sequences identified a highly conserved motif, IYTSGTTGXPK, also found in a number of proteins that form adenylated intermediates. We demonstrate that depletion of intracellular ATP dramatically reduces FATP-mediated LCFA uptake. Furthermore, wild-type FATP specifically binds [alpha-32P]azido-ATP. Introduction of a serine to alanine substitution (S250A) in the IYTSGTTGXPK motif produces an appropriately expressed and metabolized mutant FATP that demonstrates diminished LCFA transport function and decreased [alpha-32P]azido-ATP binding. These results are consistent with a mechanism of action for FATP involving ATP binding that is dependent on serine 250 of the IYTSGTTGXPK motif.

FastTag Nucleic Acid Labeling System: a versatile method for incorporating haptens, fluorochromes and affinity ligands into DNA, RNA and oligonucleotides.

The FastTag Nucleic Acid Labeling System couples haptens, fluorochromes or affinity ligands to any nucleic acid by attaching a universal, photo-or heat-activatable moiety to which any sulfhydryl-reactive compound can be linked. To demonstrate the versatility of the FastTag system, we have labeled DNA, RNA and oligonucleotide probes with a variety of maleimide-coupled moieties and have used these probes in several applications. In Southern hybridization analyses, RNA probes labeled using FastTag FL (fluorescein) detected 0.04 pg of target DNA. Human satellite DNA clones labeled using FastTag FL or FastTag Biotin detected the corresponding sequences in human chromosome spreads and interphase nuclei by fluorescence in situ hybridization. An antisense oligonucleotide probe cocktail complementary to human proinsulin transcripts labeled using FastTag DNP (dinitrophenyl) detected, in situ, the appropriate transcripts in pancreatic tissue sections. Oligonucleotide primers labeled with FastTag FL were used to PCR-amplify a genomic DNA fragment, which was then detected immunologically. Finally, we discuss how DNA labeled with FastTag Fucose can be bound to a fucose-binding affinity matrix and eluted under mild conditions.

Comparison of the ligand-binding properties of native and copper-less cytochromes bo from Escherichia coli.

The binding of four anionic ligands, cyanide, fluoride, azide and formate, to cytochrome bo purified from Escherichia coli cells grown with a copper supplement (+Cu cyt.bo) is described. Membrane-bound cytochrome bo that lacks the copper component, CuB, of its active site can be prepared from cells grown under conditions where the availability of copper is limited by the presence of a CuI chelator, 2,2'-bicinchinonic acid. The ligand-binding properties of this copper-less enzyme (-Cu cyt.bo) are compared with those of +Cu cyt. bo. As judged from near-UV/visible spectroscopic changes, cyanide forms a low-spin complex with +Cu cyt.bo, whereas azide, fluoride and formate form high-spin complexes. The pH-dependences of binding suggest that for all four of these anionic ligands, both the rates of binding and the binding affinities are primarily dependent on the concentration of their protonated forms. -Cu cyt.bo, which shows less than 15% of the duroquinol oxidase activity of +Cu cyt.bo, binds cyanide, azide and fluoride, but with greatly decreased affinity (<1/30, 1/2000 and 1/2500 respectively at pH5.5 compared with +Cu cyt.bo). The complex of azide with -Cu cyt.bo still seems to be high-spin and azide binding to -Cu cyt.bo is still pH-dependent, although less so than azide binding to +Cu cyt.bo.