Stress sensor triggers conformational response of the integral membrane protein microsomal glutathione transferase 1

Microsomal glutathione (GSH) transferase 1 (MGST1) is a trimeric, integral membrane protein involved in cellular response to chemical or oxidative stress. The cytosolic domain of MGST1 harbors the GSH binding site and a cysteine residue (C49) that acts as a sensor of oxidative and chemical stress. Spatially resolved changes in the kinetics of backbone amide H/D exchange reveal that the binding of a single molecule of GSH/trimer induces a cooperative conformational transition involving movements of the transmembrane helices and a reordering of the cytosolic domain. Alkylation of the stress sensor preorganizes the helices and facilitates the cooperative transition resulting in catalytic activation.     

Specific modification of two tryptophans within the nuclear-encoded subunits of bovine cytochrome c oxidase by hydrogen peroxide

Hydrogen peroxide does more than react with the binuclear center of oxidized bovine cytochrome c oxidase and generate the well-characterized "peroxy" and "ferryl" forms. Hydrogen peroxide also inactivates detergent-solubilized cytochrome c oxidase in a time- and concentration-dependent manner. There is a 70-80% decrease of electron-transport activity, peroxidation of bound cardiolipin, modification of two nuclear-encoded subunits (IV and VIIc), and dissociation of approximately 60% of subunits VIa and VIIa. Modification of subunit VIIc and dissociation of subunit VIIa are coupled events that probably are responsible for the inactivation of cytochrome c oxidase. When cytochrome c oxidase is exposed to 500 microM hydrogen peroxide for 30 min at pH 7.4 and room temperature, subunits IV (modified up to 20%) and VIIc (modified up to 70%) each have an increased mass of 16 Da as detected by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry and electrospray ionization mass spectrometry. In each case, the increased mass is caused by oxidation of a tryptophan (Trp19 within subunit VIIc and Trp48 within subunit IV), almost certainly due to formation of hydroxytryptophan. We conclude that hydrogen peroxide-induced oxidation of tryptophan and cardiolipin proceeds via the binuclear center since both modifications are prevented if the binuclear center is first blocked with cyanide. Bound cardiolipin and oxidized tryptophans are localized relatively far from the binuclear center (30-60 A); therefore, oxidation probably occurs by migration of a free radical generated at the binuclear center to these distal reaction sites.     

DNA double-strand breaks induce deletion of CTG.CAG repeats in an orientation-dependent manner in Escherichia coli

The influences of double-strand breaks (DSBs) within a triplet repeat sequence on its genetic instabilities (expansions and deletions) related to hereditary neurological diseases was investigated. Plasmids containing 43 or 70 CTG.CAG repeats or 43 CGG.CCG repeats were linearized in vitro near the center of the repeats and were transformed into parental, RecA-dependent homologous recombination-deficient, or RecBC exonuclease-deficient Escherichia coli. The resulting repair process considerably increased deletion of the repeating sequence compared to the circular DNA controls. Unexpectedly, the orientation of the insert relative to the unidirectional ColE1 origin of replication affected the amount of instability generated during the repair of the DSB. When the CTG strand was the template for lagging-strand synthesis, instability was increased, most markedly in the recA- strain. Results indicated that RecA and/or RecBC might play a role in DSB repair within the triplet repeat. Altering the length, orientation, and sequence composition of the triplet repeat suggested an important role of DNA secondary structures during repair intermediates. Hence, we hypothesize that ColE1 origin-dependent replication was involved during the repair of the DSB. A model is presented to explain the mechanisms of the observed genetic instabilities.     

The Human Papillomavirus Type 16 E5 Oncoprotein Inhibits Epidermal Growth Factor Trafficking Independently of Endosome Acidification

The human papillomavirus type 16 E5 oncoprotein (16E5) enhances acute, ligand-dependent activation of the epidermal growth factor receptor (EGFR) and concomitantly alkalinizes endosomes, presumably by binding to the 16-kDa “c” subunit of the V-ATPase proton pump (16K) and inhibiting V-ATPase function. However, the relationship between 16K binding, endosome alkalinization, and altered EGFR signaling remains unclear. Using an antibody that we generated against 16K, we found that 16E5 associated with only a small fraction of endogenous 16K in keratinocytes, suggesting that it was unlikely that E5 could significantly affect V-ATPase function by direct inhibition. Nevertheless, E5 inhibited the acidification of endosomes, as determined by a new assay using a biologically active, pH-sensitive fluorescent EGF conjugate. Since we also found that 16E5 did not alter cell surface EGF binding, the number of EGFRs on the cell surface, or the endocytosis of prebound EGF, we postulated that it might be blocking the fusion of early endosomes with acidified vesicles. Our studies with pH-sensitive and -insensitive fluorescent EGF conjugates and fluorescent dextran confirmed that E5 prevented endosome maturation (acidification and enlargement) by inhibiting endosome fusion. The E5-dependent defect in vesicle fusion was not due to detectable disruption of actin, tubulin, vimentin, or cytokeratin filaments, suggesting that membrane fusion was being directly affected rather than vesicle transport. Perhaps most importantly, while bafilomycin A₁ (like E5) binds to 16K and inhibits endosome acidification, it did not mimic the ability of E5 to inhibit endosome enlargement or the trafficking of EGF. Thus, 16E5 alters EGF endocytic trafficking via a pH-independent inhibition of vesicle fusion.High-risk human papillomaviruses (HPVs) are the causative agent of cervical cancer (63) and HPV type 16 (HPV-16) is associated with a majority of cervical malignancies worldwide (13). HPV-16 encodes three oncoproteins: E5, E6, and E7. While the contributions of E6 and E7 to cellular immortalization and transformation have been characterized in detail (20), the role of HPV-16 E5 (16E5) is poorly understood (53). Nevertheless, a number of studies suggest that 16E5 does contribute to the development of cervical cancer. Most high-risk HPV types encode an E5 protein (48), and targeted expression of the three HPV-16 oncogenes in basal epithelial cells of transgenic mice (4) leads to a higher incidence of cervical cancer than does the expression of E6 and E7 alone (44). In addition, targeted epithelial expression of 16E5 (without E6 and E7) in transgenic mice induces skin tumors (21). It may be noteworthy that unlike high-risk HPV-18, which integrates into the host DNA and potentially disrupts E5 gene expression (20, 64), the HPV-16 genome often persists in episomal form in malignant lesions (12, 16, 24, 36, 42).Biological activities of 16E5 that may facilitate carcinogenesis include evading host immune detection by interfering with the transport of antigen-presenting major histocompatibility complex (MHC) class I molecules to the cell surface (6), promoting anchorage-independent growth (33, 41, 52) and disrupting gap junctions responsible for cell-cell communication (37, 58). The 16E5 phenotype most frequently linked to the development of cancer is enhanced ligand-dependent activation of the epidermal growth factor receptor (EGFR) (15, 41, 46, 52). 16E5 stimulates EGF-dependent cell proliferation in vitro (7, 33, 40, 41, 52, 60) and in vivo (21), which might expand the population of basal or stemlike keratinocytes and thereby increase the probability that some of these cells would undergo malignant transformation. A number of studies indicate that 16E5 may enhance ligand-dependent EGFR activation by interfering with the acidification of early endosomes containing EGF bound to activated EGFRs (17, 51, 57). It has been hypothesized that 16E5 inhibits the H⁺ V-ATPase responsible for maintaining an acidic luminal pH in late endosomes and lysosomes (28) by associating with the V-ATPase 16-kDa “c” subunit (16K) (1, 5, 14, 22, 46) and disrupting assembly of the V-ATPase integral (V_o) and peripheral (V_i) subcomplexes (10). In contrast, Thomsen et al. (57) reported that 16E5 inhibits early endosome trafficking in fibroblasts by completely depolymerizing actin microfilaments.Due to the unavailability of antibodies that recognize native 16E5 and 16K, direct association of 16E5 with 16K has only been observed by overexpressing epitope-tagged forms of both proteins in vitro (5, 46) or in vivo (1, 14, 22). It is uncertain, therefore, whether these associations occur when the proteins are expressed at “physiological” levels. In yeast, both wild-type 16E5 (10) and several 16E5 mutants that associate with 16K in COS cells (1) inhibit vacuolar acidification, although another study in yeast concludes the opposite (5). 16K is a component of the V-ATPase V_o subcomplex, which is assembled in the endoplasmic reticulum (ER) (28), and 16E5 localizes to the ER and nuclear envelope in epithelial cells (32, 54). Thus, the export of V_o from the ER could potentially be inhibited by a significant level of 16K binding to 16E5, although the differential alkalinization of endosomes rather than the Golgi apparatus (17) would require specificity for those proton pumps directed to those sites.In the present study, we generated an antibody against native 16K and used it to determine whether 16K/16E5 complexes formed in primary keratinocytes. We also synthesized a new pH-sensitive fluorescent EGF conjugate to evaluate whether there was a correlation between E5-induced EGFR activation, trafficking and endosome alkalinization. Finally, we simultaneously monitored EGFR endocytic trafficking (using pH-insensitive fluorescent EGF), endosome fusion (using fluorescent EGF and dextran), and the status of cellular filaments and microtubules to evaluate whether E5 might disrupt some of these structures that mediate vesicle transport.     

Cyclometalated ruthenium(II) complexes of benzo[h]quinoline (bzqH)[Ru(bzq)(NCMe)4], [Ru(bzq)(LL)(NCMe)2], and [Ru(bzq)(LL)2] (LL = bpy, phen)

Cyclometalation of benzo[h]quinoline (bzqH) by [RuCl(μ-Cl)(η⁶-C₆H₆)]₂ in acetonitrile occurs in a similar way to that of 2-phenylpyridine (phpyH) to afford [Ru(bzq)(MeCN)₄]PF₆ (3) in 52% yield. The properties of 3 containing ‘non-flexible’ benzo[h]quinoline were compared with the corresponding [Ru(phpy)(MeCN)₄]PF₆ (1) complex with ‘flexible’ 2-phenylpyridine. The [Ru(phpy)(MeCN)₄]PF₆ complex is known to react in MeCN solvent with ‘non-flexible’ diimine 1,10-phenanthroline to form [Ru(phpy)(phen)(MeCN)₂]PF₆, being unreactive toward ‘flexible’ 2,2′-bipyridine under the same conditions. In contrast, complex 3 reacts both with phen and bpy in MeCN to form [Ru(bzq)(LL)(MeCN)₂]PF₆ {LL = bpy (4) and phen (5)}. Similar reaction of 3 in methanol results in the substitution of all four MeCN ligands to form [Ru(bzq)(LL)₂]PF₆ {LL = bpy (6) and phen (7)}. Photosolvolysis of 4 and 5 in MeOH occurs similarly to afford [Ru(bzq)(LL)(MeCN)(MeOH)]PF₆ as a major product. This contrasts with the behavior of [Ru(phpy)(LL)(MeCN)₂]PF₆, which lose one and two MeCN ligands for LL = bpy and phen, respectively. The results reported demonstrate a profound sensitivity of properties of octahedral compounds to the flexibility of cyclometalated ligand. Analogous to the 2-phenylpyridine counterparts, compounds 4-7 are involved in the electron exchange with reduced active site of glucose oxidase from Aspergillus niger. Structure of complexes 4 and 6 was confirmed by X-ray crystallography.     

AMPK activation restores the stimulation of glucose uptake in an in vitro model of insulin-resistant cardiomyocytes via the activation of protein kinase B

Diabetic hearts are known to be more susceptible to ischemic disease. Biguanides, like metformin, are known antidiabetic drugs that lower blood glucose concentrations by decreasing hepatic glucose production and increasing glucose disposal in muscle. Part of these metabolic effects is thought to be mediated by the activation of AMP-activated protein kinase (AMPK). In this work, we studied the relationship between AMPK activation and glucose uptake stimulation by biguanides and oligomycin, another AMPK activator, in both insulin-sensitive and insulin-resistant cardiomyocytes. In insulin-sensitive cardiomyocytes, insulin, biguanides and oligomycin were able to stimulate glucose uptake with the same efficiency. Stimulation of glucose uptake by insulin or biguanides was correlated to protein kinase B (PKB) or AMPK activation, respectively, and were additive. In insulin-resistant cardiomyocytes, where insulin stimulation of glucose uptake was greatly reduced, biguanides or oligomycin, in the absence of insulin, induced a higher stimulation of glucose uptake than that obtained in insulin-sensitive cells. This stimulation was correlated with the activation of both AMPK and PKB and was sensitive to the phosphatidylinositol-3-kinase/PKB pathway inhibitors. Finally, an adenoviral-mediated expression of a constitutively active form of AMPK increased both PKB phosphorylation and glucose uptake in insulin-resistant cardiomyocytes. We concluded that AMPK activators, like biguanides and oligomycin, are able to restore glucose uptake stimulation, in the absence of insulin, in insulin-resistant cardiomyocytes via the additive activation of AMPK and PKB. Our results suggest that AMPK activation could restore normal glucose metabolism in diabetic hearts and could be a potential therapeutic approach to treat insulin resistance.     

Transmembrane topology of FRO2, a ferric chelate reductase from Arabidopsis thaliana

Iron uptake in Arabidopsis thaliana is mediated by ferric chelate reductase FRO2, a transmembrane protein belonging to the flavocytochrome b family. There is no high resolution structural information available for any member of this family. We have determined the transmembrane topology of FRO2 experimentally using the alkaline phosphatase fusion method. The resulting topology is different from that obtained by theoretical predictions and contains 8 transmembrane helices, 4 of which build up the highly conserved core of the protein. This core is present in the entire flavocytochrome b family. The large water soluble domain of FRO2, which contains NADPH, FAD and oxidoreductase sequence motifs, was located on the inside of the membrane.Electronic Supplementary Material Supplementary material is available to authorised users in the online version of this article at This work was supported by grants from the Swedish Research Council (VR) to S. Al-Karadaghi and Hans Hebert.     

Regulated specific proteolysis of the Cajal body marker protein coilin

Cajal bodies (CB) are subnuclear domains that contain various proteins with diverse functions including the CB marker protein coilin. In this study, we investigate the proteolytic activity of calpain on coilin. Here, we report a 28-kDa cleaved coilin fragment detected by two coilin antibodies that is cell cycle regulated, with levels that are consistently reduced during mitosis. We further show that an in vitro calpain assay with full-length or C-terminal coilin recombinant protein releases the same size cleaved fragment. Furthermore, addition of exogenous RNA to purified coilin induces proteolysis by calpain. We also report that the relative levels of this cleaved coilin fragment are susceptible to changes induced by various cell stressors, and that coilin localization is affected by inhibition or knockdown of calpain both under normal and stressed conditions. Collectively, our data suggest that coilin is subjected to regulated specific proteolysis by calpain, and this processing may play a role in the regulation of coilin activity and CB formation.     

Genome sequence of the bacteriocin-producing Lactobacillus curvatus strain CRL705

Lactobacillus curvatus is one of the most prevalent lactic acid bacteria found in fermented meat products. Here, we present the draft genome sequence of Lactobacillus curvatus CRL705, a bacteriocin producer strain isolated from an Argentinean artisanal fermented sausage, which consists of 1,833,251 bp (GC content, 41.9%) and two circular plasmids of 12,342 bp (pRC12; GC, 43.9%) and 18,664 bp (pRC18; GC, 34.4%).     

Association between history and physical examination factors and change in lumbar multifidus muscle thickness after spinal manipulation in patients with low back pain

Understanding the clinical characteristics of patients with low back pain (LBP) who display improved lumbar multifidus (LM) muscle function after spinal manipulative therapy (SMT) may provide insight into a potentially synergistic interaction between SMT and exercise. Therefore, the purpose of this study was to identify the baseline historical and physical examination factors associated with increased contracted LM muscle thickness one week after SMT. Eighty-one participants with LBP underwent a baseline physical examination and ultrasound imaging assessment of the LM muscle during submaximal contraction before and one week after SMT. The relationship between baseline examination variables and 1-week change in contracted LM thickness was assessed using correlation analysis and hierarchical multiple linear regression. Four variables best predicted the magnitude of increases in contracted LM muscle thickness after SMT. When combined, these variables suggest that patients with LBP, (1) that are fairly acute, (2) have at least a moderately good prognosis without focal and irritable symptoms, and (3) exhibit signs of spinal instability, may be the best candidates for a combined SMT and lumbar stabilization exercise (LSE) treatment approach.