The beta subunit of the Na+/K+-ATPase follows the conformational state of the holoenzyme

The Na+/K+-ATPase is a ubiquitous plasma membrane ion pump that utilizes ATP hydrolysis to regulate the intracellular concentration of Na+ and K+. It is comprised of at least two subunits, a large catalytic alpha subunit that mediates ATP hydrolysis and ion transport, and an ancillary beta subunit that is required for proper trafficking of the holoenzyme. Although processes mediated by the alpha subunit have been extensively studied, little is known about the participation of the beta subunit in conformational changes of the enzyme. To elucidate the role of the beta subunit during ion transport, extracellular amino acids proximal to the transmembrane region of the sheep beta1 subunit were individually replaced for cysteines. This enabled sulfhydryl-specific labeling with the environmentally sensitive fluorescent dye tetramethylrhodamine-6-maleimide (TMRM) upon expression in Xenopus oocytes. Investigation by voltage-clamp fluorometry identified three reporter positions on the beta1 subunit that responded with fluorescence changes to alterations in ionic conditions and/or membrane potential. These experiments for the first time show real-time detection of conformational rearrangements of the Na+/K+-ATPase through a fluorophore-labeled beta subunit. Simultaneous recording of presteady-state or stationary currents together with fluorescence signals enabled correlation of the observed environmental changes of the beta subunit to certain reaction steps of the Na+/K+-ATPase, which involve changes in the occupancy of the two principle conformational states, E1P and E2P. From these experiments, evidence is provided that the beta1-S62C mutant can be directly used to monitor the conformational state of the enzyme, while the F64C mutant reveals a relaxation process that is triggered by sodium transport but evolves on a much slower time scale. Finally, shifts in voltage dependence and kinetics observed for mutant K65C show that this charged lysine residue, which is conserved in beta1 isoforms, directly influences the effective potential that determines voltage dependence of extracellular cation binding and release.

EZH2 and histone 3 trimethyl lysine 27 associated with Il4 and Il13 gene silencing in Th1 cells

Differentiation of naïve CD4 T cells toward the T helper 1 (T(H)1) and T helper 2 (T(H)2) fates involves the transcriptional repression and enhancement, respectively, of Il4 and Il13, adjacent chromosome 11 genes encoding the canonical T(H)2 cytokines interleukin-4 and interleukin-13. Proper execution of this developmental fate choice during immune responses is critical to host defense and, when misregulated, leads to susceptibility to infectious microbes and to allergic and autoimmune diseases. Here, using chromatin immunoprecipitation and real time reverse transcription PCR we identify the Polycomb family histone methyltransferase EZH2 as the enzyme responsible for methylating lysine 27 of histone H3 at the Il4-Il13 locus of T(H)1 but not T(H)2 cells, implicating EZH2 in the mechanism of Il4 and Il13 transcriptional silencing.

Lipid phosphate phosphatase-1 regulates lysophosphatidic acid-induced calcium release, NF-kappaB activation and interleukin-8 secretion in human bronchial epithelial cells

LPA (lysophosphatidic acid), a potent bioactive phospholipid, elicits diverse cellular responses through activation of the G-protein-coupled receptors LPA1-LPA4. LPA-mediated signalling is partially regulated by LPPs (lipid phosphate phosphatases; LPP-1, -2 and -3) that belong to the phosphatase superfamily. This study addresses the role of LPPs in regulating LPA-mediated cell signalling and IL-8 (interleukin-8) secretion in HBEpCs (human bronchial epithelial cells). Reverse transcription-PCR and Western blotting revealed the presence and expression of LPP-1-3 in HBEpCs. Exogenous [3H]oleoyl LPA was hydrolysed to [3H]-mono-oleoylglycerol. Infection of HBEpCs with an adenoviral construct of human LPP-1 for 48 h enhanced the dephosphorylation of exogenous LPA by 2-3-fold compared with vector controls. Furthermore, overexpression of LPP-1 partially attenuated LPA-induced increases in the intracellular Ca2+ concentration, phosphorylation of IkappaB (inhibitory kappaB) and translocation of NF-kappaB (nuclear factor-kappaB) to the nucleus, and almost completely prevented IL-8 secretion. Infection of cells with an adenoviral construct of the mouse LPP-1 (R217K) mutant partially attenuated LPA-induced IL-8 secretion without altering LPA-induced changes in intracellular Ca2+ concentration, phosphorylation of IkappaB, NF-kappaB activation or IL-8 gene expression. Our results identify LPP-1 as a key regulator of LPA signalling and IL-8 secretion in HBEpCs. Thus LPPs could represent potential targets in regulating leucocyte infiltration and airway inflammation.

Studies of SpoIIAB mutant proteins elucidate the mechanisms that regulate the developmental transcription factor sigmaF in Bacillus subtilis

SigmaF, the first compartment-specific sigma factor of sporulation, is regulated by an anti-sigma factor, SpoIIAB (AB) and its antagonist SpoIIAA (AA). AB can bind to sigmaF in the presence of ATP or to AA in the presence of ADP; in addition, AB can phosphorylate AA. The ability of AB to switch between its two binding partners regulates sigmaF. Early in sporulation, AA activates sigmaF by releasing it from its complex with AB. We have previously proposed a reaction scheme for the phosphorylation of AA by AB which accounts for AA's regulatory role. A crucial feature of this scheme is a conformational change in AB that accompanies its switch in binding partner. In the present study, we have studied three AB mutants, all of which have amino-acid replacements in the nucleotide-binding region; AB-E104K (Glu104-->Lys) and AB-T49K (Thr49-->Lys) fail to activate sigmaF, and AB-R105A (Arg105-->Ala) activates it prematurely. We used techniques of enzymology, surface plasmon resonance and fluorescence spectroscopy to analyse the defects in each mutant. AB-E104K was deficient in binding to AA, AB-T49K was deficient in binding to ADP and AB-R105A bound ADP exceptionally strongly. Although the release of sigmaF from all three mutant proteins was impaired, and all three failed to undergo the wild-type conformational change when switching binding partners, the phenotypes of the mutant cells were best accounted for by the properties of the respective AB species in forming complexes with AA and ADP. The behaviour of the mutants enables us to propose convincing mechanisms for the regulation of sigmaF in wild-type bacteria.

Impaired penicillin production in lysine regulatory mutants of Penicillium chrysogenum

Lysine-regulatory mutants of Penicillium chrysogenum which excrete lysine were found to be deficient in production of penicillin. A revertant recovered the ability to produce penicillin.

Apoptotic killing of fibroblasts by matrix-bound advanced glycation endproducts

The extracellular matrix accumulates biologically active advanced glycation endproducts such as carboxymethyl-lysine (CML). Alikhani et al. recently reported that CML-rich collagen, representing an artifically aged matrix protein, induces apoptosis in vivo and in fibroblasts. This observation may have profound implications for the biology of cell-matrix interactions during aging.

Engineering lysine reactivity as a conformational sensor in the Dictyostelium myosin II motor domain

Lys84 of skeletal muscle myosin located at the interface between the motor and neck domains has long been utilized as a useful chemical probe sensing motor domain conformational changes and tilting of the lever arm. Here we report the first site-directed mutagenesis study on this side chain and its immediate chemical environment. We made Dictyostelium myosin II motor domain constructs in which Lys84 was replaced by either a methionine or a glutamic acid residue and another mutant containing an Arg704Glu substitution. By following trinitrophenylation of the mutant constructs, we first unambiguously identify Lys84 as the reactive lysine in Dictyostelium myosin. Analysis of the reaction profiles also reveals that the Lys84-Arg704 interaction at the interface of two subdomains of the myosin head has a significant effect on Lys84 reactivity, but it is not the only determinant of this property. Our findings imply that the nucleotide sensitivity of the trinitrophenylation reaction is a general feature of conventional myosins that reflects similar changes in the conformational dynamics of the different orthologs during the ATPase cycle.

Lysine requirement of kittens given purified diets for maximal growth

Three experiments were conducted using a total of 15 male and 15 female weaned specific pathogen-free kittens given amino acid-based purified diets containing varying concentrations of lysine (from 4.0 to 11.3 g/kg diet) in a Latin square design of 10 day periods. In experiment 1, the predicted lysine requirement was 7.7 g/kg diet, and in experiments 2 and 3, maximal weight gain occurred at 8.0 g lysine/kg diet. In experiment 3, nitrogen balance was not different for kittens given diets containing 8.0 and 9.0 g lysine/kg. These experiments support a requirement of 8.0 g lysine (free base)/kg diet, in a diet with a calculated metabolizable energy value of 4.7 kcal/g.

Critical role of lysine 204 in switch I region of Galpha13 for regulation of p115RhoGEF and leukemia-associated RhoGEF

Heterotrimeric G proteins of the G12 family regulate the Rho GTPase through RhoGEFs that contain an amino-terminal regulator of G protein signaling (RGS) domain (RGS-RhoGEFs). Direct regulation of the activity of RGS-RhoGEFs p115 or leukemia-associated RhoGEF (LARG) by Galpha13 has previously been demonstrated. However, the precise biochemical mechanism by which Galpha13 stimulates the RhoGEF activity of these proteins has not yet been well understood. Based on the crystal structure of Galphai1 in complex with RGS4, we mutated the Galpha13 residue lysine 204 to alanine (Galpha13K204A) and characterized the effect of this mutation in its regulation of RGS-RhoGEFs p115 or LARG. Compared with wild-type Galpha13, Galpha13K204A induced much less serum-response factor activation when expressed in HeLa cells. Recombinant Galpha13K204A exhibits normal function in terms of nucleotide binding, basal GTP hydrolysis, and formation of heterotrimer with betagamma. We found that lysine 204 of Galpha13 is important for interaction with the RGS domain of p115 or LARG and for the GTPase-activating protein activity of these proteins. In addition, the K204A mutation of Galpha13 impaired its regulation of the RhoGEF activity of p115 or LARG. We conclude that lysine 204 of Galpha13 is important for interaction with RGS-RhoGEFs and is critically involved in the regulation of their activity.

Lysines close to the Rous sarcoma virus late domain critical for budding

The release of retroviruses from the plasma membrane requires host factors that are believed to be recruited to the site of budding by the late (L) domain of the virus-encoded Gag protein. The L domain of Rous sarcoma virus (RSV) has been shown to interact with a ubiquitin (Ub) ligase, and budding of this virus is dependent on Ub. RSV is similar to other retroviruses in that it contains approximately 100 molecules of Ub, but it is unique in that none of these molecules has been found to be conjugated to Gag. If transient ubiquitination of RSV Gag is required for budding, then replacement of the target lysine(s) with arginine should prevent the addition of Ub and reduce budding. Based on known sites of ubiquitination in other viruses, the important lysines would likely reside near the L domain. In RSV, there are five lysines located just upstream of the L domain in a region of the matrix (MA) protein that is dispensable for membrane binding, and replacement of these with arginine (mutant 1-5KR) reduced budding 80 to 90%. The block to budding was found to be on the plasma membrane; however, the few virions that were released had normal size, morphology, and infectivity. Budding was restored when any one of the residues was changed back to lysine or when lysines were inserted in novel positions, either within this region of MA or within the downstream p10 sequence. Moreover, the 1-5KR mutant could be rescued into particles by coexpression of budding-competent Gag molecules. These data argue that the phenotype of mutant 1-5KR is not due to a conformational defect. Consistent with the idea that efficient budding requires a specific role for lysines, human T-cell leukemia virus type 1, which does not bud well compared to RSV and lacks lysines close to its L domain, was found to be released at a higher level upon introduction of lysines near its L domain. This report strongly supports the hypothesis that ubiquitination of the RSV Gag protein (and perhaps those of other retroviruses) is needed for efficient budding.

N -(Carboxymethyl)lysine and 3-DG-Imidazolone Are Major AGE Structures in Protein Modification by 3-Deoxyglucosone

The levels of plasma 3-deoxyglucosone (3-DG) increase under hyperglycemic conditions and are associated with the pathogenesis of diabetic complications because of the high reactivity of 3-DG with proteins to form advanced glycation end products (AGE). To investigate potential markers for 3-DG-mediated protein modification in vitro and in vivo, we compared the yield of several 3-DG-derived AGE structures by immunochemical analysis and HPLC and measured their localization in human atherosclerotic lesions. When BSA was incubated with 3-DG at 37 degrees C for up to 4 wk, the amounts of N(epsilon)-(carboxymethyl)lysine (CML) and 3-DG-imidazolone steeply increased with incubation time, whereas the levels of pyrraline and pentosidine increased slightly by day 28. In contrast, significant amounts of pyrraline and pentosidine were also observed when BSA was incubated with 3-DG at 60 degrees C to enhance AGE-formation. In atherosclerotic lesions, CML and 3-DG-imidazolone were found intracellularly in the cytoplasm of most foam cells and extracellularly in the atheromatous core. A weak-positive immunoreaction with pyrraline was found in the extracellular matrix and a few foam cells in aortic intima with atherosclerotic lesions. Our results provide the first evidence that CML and 3-DG-imidazolone are major AGE structures in 3-DG-modified proteins, and that 3-DG-imidazolone provides a better marker for protein modification by 3-DG than pyrraline.

K103N Mutation in Antiretroviral Therapy--Naive African Patients Infected with HIV Type 1

Most of the information about genetic sequencing and drug susceptibility of human immunodeficiency virus type 1 (HIV-1) is derived from the study of HIV-1 subtype B. Worldwide, most people infected with HIV-1 are infected with non-subtype B viruses and live in developing countries. We report 3 cases of antiretroviral-naive African immigrants infected with HIV-1 strains possessing the K103N mutation in the reverse transcriptase gene, which confers high-level resistance to all nonnucleoside reverse transcriptase inhibitors.

AcK-knowledge Reversible Acetylation

In 1966, the histone was identified as the first protein subject to reversible acetylation. The ensuing 30 years of research on histone acetylation has been critical for elucidating how gene transcription and chromatin remodeling are regulated at the molecular level. This central focus on histones, however, has also restricted our understanding of reversible acetylation, and therefore the enzymes that catalyze this reaction, to cellular processes predominantly associated with chromatin. The study of reversible acetylation has become more or less synonymous with histone acetylation. Recent developments-including increased ability to detect acetylated proteins, the characterization of novel acetyltransferases and deacetylases, and the identification of specific inhibitors for these enzymes-have revealed that this histone-central paradigm probably reflects only a fraction of the cellular processes regulated by reversible acetylation. New studies have uncovered unexpected roles for reversible acetylation in many diverse areas, thereby establishing protein acetylation as a highly versatile signaling modification that has functions beyond gene transcription and chromatin remodeling.

Amino terminal glutamate residues confer spermine sensitivity and affect voltage gating and channel conductance of rat connexin40 gap junctions

Connexin40 (Cx40) contains a specific binding site for spermine (affinity approximately 100 microm) whereas connexin43 (Cx43) is unaffected by identical concentrations of intracellular spermine. Replacement of two unique glutamate residues, E9 and E13, from the cytoplasmic amino terminal domain of Cx40 with the corresponding lysine residues from Cx43 eliminated the block by 2 mm spermine, reduced the transjunctional voltage (V(j)) gating sensitivity, and reduced the unitary conductance of this Cx40E9,13K gap junction channel protein. The single point mutations, Cx40E9K and Cx40E13K, predominantly affected the residual conductance state (G(min)) and V(j) gating properties, respectively. Heterotypic pairing of Cx40E9,13K with wild-type Cx40 in murine neuro2A (N2A) cells produced a strongly rectifying gap junction reminiscent of the inward rectification properties of the Kir (e.g. Kir2.x) family of potassium channels. The reciprocal Cx43K9,13E mutant protein exhibited reduced V(j) sensitivity, but displayed much less rectification in heterotypic pairings with wtCx43, negligible changes in the unitary channel conductance, and remained insensitive to spermine block. These data indicate that the connexin40 amino terminus may form a critical cytoplasmic pore-forming domain that serves as the receptor for V(j)-dependent closure and block by intracellular polyamines. Functional reciprocity between Cx40 and Cx43 gap junctions involves other amino acid residues in addition to the E or K 9 and 13 loci located on the amino terminal domain of these two connexins.

Regulation of the anion channel of the chloroplast envelope from spinach

Several anions such as Cl-, NO2(-), SO4(2-), and PO4(3-) are known to modulate the photosynthetic activity. Moreover, the chloroplast metabolism requires the exchange of both inorganic and organic (e.g., triose phosphate, dicarboxylic acid, ATP) anions between the cytoplasm and the stroma. A chloride channel form the chloroplast envelope was reconstituted in planar lipid bilayers. We show that the channel is active in conditions prevailing in the plant. The open probability increases with the ionic strength of the experimental solutions and is maximal at 0 mV. This suggests that the channel could play a role in the osmotic regulation of the chloroplast. Amino group reagents affect the channel activity in a way that demonstrated that lysine residues are important for channel gating but not for ATP binding. Together, our results provide new information on the functioning of this channel in the chloroplast envelope membranes. They indicate that the open probability of the channel is low (Po < or = 0.2) in vivo and that this channel can account for the chloride flux through the chloroplast envelope.

NKp44 triggers NK cell activation through DAP12 association that is not influenced by a putative cytoplasmic inhibitory sequence

NKp44 (NCR2) is a member of the natural cytotoxicity receptor (NCR) family that is expressed on activated human NK cells. We dissected structural attributes of NKp44 to determine their contributions to receptor function. Our results demonstrate that surface expression and NK cell activation by NKp44 is mediated through noncovalent association with the immunoreceptor tyrosine-based activation motif-containing protein, DAP12. Physical linkage to DAP12 requires lysine-183 in the NKp44 transmembrane domain. Intriguingly, the cytoplasmic domain of NKp44 also contains a sequence that matches the immunoreceptor tyrosine-based inhibitory motif (ITIM) consensus. By expressing a chimeric receptor in an NK-like cell line, we found that this ITIM-like motif from NKp44 lacks inhibitory capacity in a redirected cytotoxicity assay. The NKp44 cytoplasmic tyrosine was efficiently phosphorylated in the chimeric receptor upon treating the cells with pervanadate, but it was unable to recruit ITIM-binding negative effector phosphatases. We also generated NK-like cell lines expressing epitope-tagged wild-type or tyrosine to phenylalanine mutant (Y238F) versions of NKp44 and compared their capacities to induce activation marker expression, promote IFN-gamma production, or stimulate target cell cytotoxicity. We did not detect any tyrosine-dependent reduction or enhancement of NK cell activation through wild-type vs. Y238F mutant NKp44. Finally, the cytoplasmic tyrosine-based sequence did not provide a docking site for the AP-2 clathrin adaptor, nor did it potentiate receptor internalization. In summary, all activating properties and surface expression of NKp44 are mediated through its association with DAP12, and the putative ITIM in the NKp44 cytoplasmic domain does not appear to attenuate activating function.

WWP1-dependent ubiquitination and degradation of the lung Krüppel-like factor, KLF2

The zinc-finger transcription factor Krüppel-like factor-2 plays an important role in pulmonary development, inhibition of adipocyte differentiation, and maintaining quiescence in single-positive T cells. KLF2 levels rapidly decrease during adipogenesis and activation of T cells, but the pathways involved remain unclear. Previously, we identified WWP1, a HECT-domain E3-ubiquitin ligase, as an interacting partner of KLF2. This led us to speculate that KLF2 may be targeted for ubiquitination. Here, we demonstrate that WWP1 interacts with KLF2 in vivo and mediates both poly-ubiquitination and proteasomal degradation of KLF2. Deleting the inhibitory domain of KLF2 abrogated KLF2-WWP1 interactions and abolished WWP1-mediated poly-ubiquitination and down-regulation of KLF2. Furthermore, lysine-121 in the inhibitory domain of KLF2 is critical for ubiquitin-conjugation. Finally, the catalytic cysteine of WWP1 is not required for KLF2-ubiquitination. Our experiments demonstrate for the first time that WWP1 promotes ubiquitination and degradation of KLF2 and is not involved in the ubiquitin-transfer reaction.

Use of a herbicide or lysine plus threonine for non-antibiotic selection of transgenic chickpea

A desensitized aspartate kinase (AK) gene has been developed as a non-antibiotic selection marker for use in the production of transgenic chickpea ( Cicer arietinum L.). Transgenic shoots regenerated from embryo explants bombarded with the desensitized AK gene were selected on media containing two amino acids, lysine and threonine (LT). Approximately 15% of the putative transgenic shoots of vars. P-362 and P-1042 survived after 4 weeks of growth on MSB5 medium (MS mineral salts and B5 vitamins) containing 2 microM thidiazuron (TDZ) and 2 mM lysine and 2 m M threonine. These shoots were subsequently grown on MSB5 medium supplemented with 2 micro M TDZ and 5 mM lysine and 5 mM threonine, and nearly 1% continued to grow after 16 weeks of selection. A phosphinothricin (PPT) selection system for Agrobacterium-mediated chickpea transformation was also developed. Three varieties of chickpea, P-362, P-1042 and P-1043, were successfully used for Agrobacterium transformation. Following Agrobacterium infection, 3-8% of the regenerated shoots remained green and continued to grow on MSB5 medium supplemented with 2.5 mg l(-1 )PPT. Increasing the concentrations of PPT to 15 mg l(-1) reduced transgenic shoot production in P-362, P-1042 and P-1043 to 0.7%, 1.2% and 1.1%, respectively. Selected putatively transformed shoots of all three varieties were rooted and grown to maturity. Southern hybridization analysis revealed single as well as multiple integration of genes in selected transgenic lines. The level of AK activity detected in LT-selected plants was higher than that detected in the non-transformed control.

Critical Role for Lysine 133 in the Nuclear Ubiquitin-mediated Degradation of MyoD

The ubiquitin-proteasome system is responsible for the regulation and turnover of the nuclear transcription factor MyoD. The degradation of MyoD can occur via an NH2 terminus-dependent pathway or a lysine-dependent pathway, suggesting that MyoD ubiquitination may be driven by different mechanisms. To understand this process, deletion analysis was used to identify the region of MyoD that is required for rapid proteolysis in the lysine-dependent pathway. Here we report that the basic helix-loop-helix domain is required for ubiquitination and lysine-dependent degradation of MyoD in the nucleus. Site-directed mutagenesis in MyoD revealed that lysine 133 is the major internal lysine of ubiquitination. The half-life of the MyoD K133R mutant protein was longer than that of wild type MyoD, substantiating the implication of lysine 133 in the turnover of MyoD in myoblasts. In addition, the MyoD K133R mutant displayed activity 2-3-fold higher than the wild type in transactivation muscle-specific gene and myogenic conversion of 10T1/2 cells. Taken together, our data demonstrate that lysine 133 is targeted for ubiquitination and rapid degradation of MyoD in the lysine-dependent pathway and plays an integral role in compromising MyoD activity in the nucleus.

The 'functional' dyad of scorpion toxin Pi1 is not itself a prerequisite for toxin binding to the voltage-gated Kv1.2 potassium channels

Pi1 is a 35-residue scorpion toxin cross-linked by four disulphide bridges that acts potently on both small-conductance Ca2+-activated (SK) and voltage-gated (Kv) K+ channel subtypes. Two approaches were used to investigate the relative contribution of the Pi1 functional dyad (Tyr-33 and Lys-24) to the toxin action: (i) the chemical synthesis of a [A24,A33]-Pi1 analogue, lacking the functional dyad, and (ii) the production of a Pi1 analogue that is phosphorylated on Tyr-33 (P-Pi1). According to molecular modelling, this phosphorylation is expected to selectively impact the two amino acid residues belonging to the functional dyad without altering the nature and three-dimensional positioning of other residues. P-Pi1 was directly produced by peptide synthesis to rule out any possibility of trace contamination by the unphosphorylated product. Both Pi1 analogues were compared with synthetic Pi1 for bioactivity. In vivo, [A24,A33]-Pi1 and P-Pi1 are lethal by intracerebroventricular injection in mice (LD50 values of 100 and 40 microg/mouse, respectively). In vitro, [A24,A33]-Pi1 and P-Pi1 compete with 125I-apamin for binding to SK channels of rat brain synaptosomes (IC50 values of 30 and 10 nM, respectively) and block rat voltage-gated Kv1.2 channels expressed in Xenopus laevis oocytes (IC50 values of 22 microM and 75 nM, respectively), whereas they are inactive on Kv1.1 or Kv1.3 channels at micromolar concentrations. Therefore, although both analogues are less active than Pi1 both in vivo and in vitro, the integrity of the Pi1 functional dyad does not appear to be a prerequisite for the recognition and binding of the toxin to the Kv1.2 channels, thereby highlighting the crucial role of other toxin residues with regard to Pi1 action on these channels. The computed simulations detailing the docking of Pi1 peptides on to the Kv1.2 channels support an unexpected key role of specific basic amino acid residues, which form a basic ring (Arg-5, Arg-12, Arg-28 and Lys-31 residues), in toxin binding.

Gonadotropin releasing hormone (GnRH) modulates odorant responses in the peripheral olfactory system of axolotls

Peripheral signal modulation plays an important role in sensory processing. Activity in the vertebrate olfactory epithelium may be modulated by peptides released from the terminal nerve, such as gonadotropin releasing hormone (GnRH). Here, we demonstrate that GnRH modulates odorant responses in aquatic salamanders (axolotls, Ambystoma mexicanum). We recorded electrical field potentials (electro-olfactograms, or EOGs) in response to stimulation with four different amino acid odorants, L-lysine, L-methionine, L-cysteine, and L-glutamic acid. EOG responses were recorded from the main olfactory epithelium before, during, and after application of 10 microM GnRH. This protocol was repeated for a total of three trials with 60-80 min between trials. The effect of GnRH on EOG responses was broadly similar across odorants and across trials. In general, EOG responses were reduced to 79% of the initial magnitude during application of GnRH; in some trials in which glutamic acid served as the odorant, EOG responses were enhanced during the wash period. Although the 4-min inter-stimulus interval did not lead to adaptation of EOG responses during the first trial, we frequently observed evidence of adaptation during the second and third trials. In addition, we found that lower concentrations of GnRH produced a smaller effect. These results demonstrate that GnRH can modulate odorant responses in the peripheral olfactory system.

PML residue lysine 160 is required for the degradation of PML induced by herpes simplex virus type 1 regulatory protein ICP0

During the early stages of herpes simplex virus type 1 (HSV-1) infection, viral immediate-early regulatory protein ICP0 localizes to and disrupts cellular nuclear structures known as PML nuclear bodies or ND10. These activities correlate with the functions of ICP0 in stimulating lytic infection and reactivating quiescent HSV-1. The disruption of ND10 occurs because ICP0 induces the loss of the SUMO-1-modified forms of PML and the subsequent proteasome-mediated degradation of the PML protein. The functions of ICP0 are largely dependent on the integrity of its zinc-binding RING finger domain. Many RING finger proteins have been found to act as ubiquitin E3 ligase enzymes, stimulating the production of conjugated polyubiquitin chains in the presence of ubiquitin, the ubiquitin-activating enzyme E1, and the appropriate E2 ubiquitin-conjugating enzyme. Substrate proteins that become polyubiquitinated are then subject to degradation by proteasomes. We have previously shown that purified full-length ICP0 acts as an efficient E3 ligase in vitro, producing high-molecular-weight polyubiquitin chains in a RING finger-dependent but substrate-independent manner. In this paper we report on investigations into the factors governing the degradation of PML induced by ICP0 in a variety of in vivo and in vitro assays. We found that ICP0 expression increases the levels of ubiquitinated PML in transfected cells. However, ICP0 does not interact with or directly ubiquitinate either unmodified PML or SUMO-1-modified PML in vitro, suggesting either that additional factors are required for the ICP0-mediated ubiquitination of PML in vivo or that PML degradation is an indirect consequence of some other activity of ICP0 at ND10. Using a transfection-based approach and a family of deletion and point mutations of PML, we found that efficient ICP0-induced PML degradation requires sequences within the C-terminal part of PML and lysine residue 160, one of the principal targets for SUMO-1 modification of the protein.