The Molecular and Physiological Effects of Protein-Derived Polyamines in the Intestine

Consumption of a high-protein diet increases protein entry into the colon. Colonic microbiota can ferment proteins, which results in the production of protein fermentation end-products, like polyamines. This review describes the effects of polyamines on biochemical, cellular and physiological processes, with a focus on the colon. Polyamines (mainly spermine, spermidine, putrescine and cadaverine) are involved in the regulation of protein translation and gene transcription. In this, the spermidine-derived hypusination modification of EIF5A plays an important role. In addition, polyamines regulate metabolic functions. Through hypusination of EIF5A, polyamines also regulate translation of mitochondrial proteins, thereby increasing their expression. They can also induce mitophagy through various pathways, which helps to remove damaged organelles and improves cell survival. In addition, polyamines increase mitochondrial substrate oxidation by increasing mitochondrial Ca2+-levels. Putrescine can even serve as an energy source for enterocytes in the small intestine. By regulating the formation of the mitochondrial permeability transition pore, polyamines help maintain mitochondrial membrane integrity. However, their catabolism may also reduce metabolic functions by depleting intracellular acetyl-CoA levels, or through production of toxic by-products. Lastly, polyamines support gut physiology, by supporting barrier function, inducing gut maturation and increasing longevity. Polyamines thus play many roles, and their impact is strongly tissue- and dose-dependent. However, whether diet-derived increases in colonic luminal polyamine levels also impact intestinal physiology has not been resolved yet.

A hypusine-eIF5A-PEAK1 switch regulates the pathogenesis of pancreatic cancer

Deregulation of protein synthesis is a hallmark of cancer cell proliferation, survival, and metastatic progression. eIF5A1 and its highly related isoform eIF5A2 are translation initiation factors that have been implicated in a range of human malignancies, but how they control cancer development and disease progression is still poorly understood. Here, we investigated how eIF5A proteins regulate pancreatic ductal adenocarcinoma (PDAC) pathogenesis. eIF5A proteins are the only known proteins regulated by a distinct posttranslational modification termed hypusination, which is catalyzed by two enzymes, deoxyhypusine synthase (DHPS) and deoxyhypusine hydroxylase (DOHH). The highly selective nature of the hypusine modification and its amenability to pharmacologic inhibition make eIF5A proteins attractive therapeutic targets. We found that the expression and hypusination of eIF5A proteins are upregulated in human PDAC tissues and in premalignant pancreatic intraepithelial neoplasia tissues isolated from Pdx-1-Cre: LSL-KRAS(G12D) mice. Knockdown of eIF5A proteins in PDAC cells inhibited their growth in vitro and orthotopic tumor growth in vivo, whereas amplification of eIF5A proteins increased PDAC cell growth and tumor formation in mice. Small-molecule inhibitors of DHPS and DOHH both suppressed eIF5A hypusination, preventing PDAC cell growth. Interestingly, we found that eIF5A proteins regulate PDAC cell growth by modulating the expression of PEAK1, a nonreceptor tyrosine kinase essential for PDAC cell growth and therapy resistance. Our findings suggest that eIF5A proteins utilize PEAK1 as a downstream effector to drive PDAC pathogenesis and that pharmacologic inhibition of the eIF5A-hypusine-PEAK1 axis may provide a novel therapeutic strategy to combat this deadly disease.

Many keys to push: diversifying the 'readership' of plant homeodomain fingers

Covalent histone modifications-referred to as the 'histone code', are recognized by a wealth of effector or 'reader' modules, representing one of the most fundamental epigenetic regulatory mechanisms that govern the structure and function of our genome. Recent progresses on combinatorial readout of such 'histone code' promote us to reconsider epigenetic regulation as a more complicated theme than we originally anticipated. In particular, plant homeodomain (PHD) fingers, which are evolved with fine-tuned residue composition and integrated or paired with other reader modules, display remarkably diverse 'readership' other than its founding-member target, histone H3 trimethylation on lysine 4 (H3K4me3). In this review, we detail the latest progresses of PHD finger research, especially from the perspective of structural biology, and highlight the versatile binding features and biological significance of PHD fingers.

C. elegans STK39/SPAK ortholog-mediated inhibition of ClC anion channel activity is regulated by WNK-independent ERK kinase signaling

Mammalian Ste20-like proline/alanine-rich kinase (SPAK) and oxidative stress-responsive 1 (OSR1) kinases phosphorylate and regulate cation-coupled Cl(-) cotransporter activity in response to cell volume changes. SPAK and OSR1 are activated via phosphorylation by upstream with-no-lysine (WNK) kinases. In Caenorhabditis elegans, the SPAK/OSR1 ortholog germinal center kinase (GCK)-3 binds to and regulates the activity of the cell volume- and meiotic cell cycle-dependent ClC anion channel CLH-3b. We tested the hypothesis that WNK kinases function in the GCK-3/CLH-3b signaling cascade. CLH-3b heterologously expressed in human embryonic kidney (HEK) cells was unaffected by coexpression with the single C. elegans WNK kinase, WNK-1, or kinase-dead WNK-1 dominant-negative mutants. RNA interference (RNAi) knockdown of the single Drosophila WNK kinase had no effect on the activity of CLH-3b expressed in Drosophila S2 cells. Similarly, RNAi silencing of C. elegans WNK-1 had no effect on basal or cell volume-sensitive activity of CLH-3b expressed endogenously in worm oocytes. Previous yeast 2-hybrid studies suggested that ERK kinases may function upstream of GCK-3. Pharmacological inhibition of ERK signaling disrupted CLH-3b activity in HEK cells in a GCK-3-dependent manner. RNAi silencing of the C. elegans ERK kinase MPK-1 or the ERK phosphorylating/activating kinase MEK-2 constitutively activated native CLH-3b. MEK-2 and MPK-1 play important roles in regulating the meiotic cell cycle in C. elegans oocytes. Cell cycle-dependent changes in MPK-1 correlate with the pattern of CLH-3b activation observed during oocyte meiotic maturation. We postulate that MEK-2/MPK-1 functions upstream from GCK-3 to regulate its activity during cell volume and meiotic cell cycle changes.

Lysine residue 185 of Rad1 is a topological but not a functional counterpart of lysine residue 164 of PCNA

Monoubiquitylation of the homotrimeric DNA sliding clamp PCNA at lysine residue 164 (PCNA^K164) is a highly conserved, DNA damage-inducible process that is mediated by the E2/E3 complex Rad6/Rad18. This ubiquitylation event recruits translesion synthesis (TLS) polymerases capable of replicating across damaged DNA templates. Besides PCNA, the Rad6/Rad18 complex was recently shown in yeast to ubiquitylate also 9-1-1, a heterotrimeric DNA sliding clamp composed of Rad9, Rad1, and Hus1 in a DNA damage-inducible manner. Based on the highly similar crystal structures of PCNA and 9-1-1, K185 of Rad1 (Rad1^K185) was identified as the only topological equivalent of PCNA^K164. To investigate a potential role of posttranslational modifications of Rad1^K185 in DNA damage management, we here generated a mouse model with a conditional deletable Rad1^K185R allele. The Rad1^K185 residue was found to be dispensable for Chk1 activation, DNA damage survival, and class switch recombination of immunoglobulin genes as well as recruitment of TLS polymerases during somatic hypermutation of immunoglobulin genes. Our data indicate that Rad1^K185 is not a functional counterpart of PCNA^K164.

Conformational effects of Lys191 in the human GnRH receptor: mutagenesis and molecular dynamics simulations studies

In the present study, we analyzed the role of Lys191 on function, structure, and dynamic behavior of the human GnRH receptor (hGnRHR) and the formation of the Cys14-Cys200 bridge, which is essential for receptor trafficking to the plasma membrane. Several mutants were studied; mutants lacked either the Cys14-Cys200 bridge, Lys191 or both. The markedly reduced expression and function of a Cys14Ser mutant lacking the 14-200 bridge, was nearly restored to wild-type/DeltaLys191 levels upon deletion of Lys191. Lys191 removal resulted in changes in the dynamic behavior of the mutants as disclosed by molecular dynamics simulations: the distance between the sulfur- (or oxygen-) sulfur groups of Cys (or Ser)14 and Cys200 was shorter and more constant, and the conformation of the NH(2)-terminus and the exoloop 2 exhibited fewer fluctuations than when Lys191 was present. These data provide novel information on the role of Lys191 in defining an optimal configuration for the hGnRHR intracellular trafficking and function.

Residue Lys57 in the collagen-like region of human L-ficolin and its counterpart Lys47 in H-ficolin play a key role in the interaction with the mannan-binding lectin-associated serine proteases and the collectin receptor calreticulin

L- and H-ficolins are serum oligomeric defense proteins consisting of a collagen-like region and a fibrinogen-like recognition domain that bind to pathogen- and apoptotic cell-associated molecular patterns. They share with mannan-binding lectin (MBL) the ability to associate with MBL-associated serine proteases (MASP)-1, -2, -3, and protein MAp19 and to trigger the lectin complement pathway through MASP-2 activation. Recent studies have revealed the essential role of Lys(55) in the collagenous region of MBL in the interaction with the MASPs and calreticulin (CRT). To test the possible involvement of the homologous residues Lys(57) of L-ficolin and Lys(47) of H-ficolin, point mutants of both proteins were produced in which these residues were mutated to Ala, Glu, or Arg. The resulting mutants exhibited oligomerization patterns and ligand binding properties similar to those of their wild-type counterparts. In contrast, all three mutations strongly inhibited the interaction of L- and H-ficolins with MAp19 and MASP-2 and impaired the ability of each ficolin to trigger the lectin pathway. In the case of MASP-1 and MASP-3, replacement of the target Lys residues by Ala or Glu abolished interaction, whereas the Lys to Arg mutations had only slight inhibitory effects. Likewise, binding of each ficolin to CRT was inhibited by mutation of Lys to Ala or Glu, but not to Arg. In conclusion, residues Lys(57) of L-ficolin and Lys(47) of H-ficolin are key components of the interaction with the MASPs and CRT, providing strong indication that MBL and the ficolins share homologous binding sites for both types of proteins.

Lysine-rich extracellular rings formed by hbeta2 subunits confer the outward rectification of BK channels

The auxiliary β subunits of large-conductance Ca²⁺-activated K⁺ (BK) channels greatly contribute to the diversity of BK (mSlo1 α) channels, which is fundamental to the adequate function in many tissues. Here we describe a functional element of the extracellular segment of hβ2 auxiliary subunits that acts as the positively charged rings to modify the BK channel conductance. Four consecutive lysines of the hβ2 extracellular loop, which reside sufficiently close to the extracellular entryway of the pore, constitute three positively charged rings. These rings can decrease the extracellular K⁺ concentration and prevent the Charybdotoxin (ChTX) from approaching the extracellular entrance of channels through electrostatic mechanism, leading to the reduction of K⁺ inflow or the outward rectification of BK channels. Our results demonstrate that the lysine rings formed by the hβ2 auxiliary subunits influences the inward current of BK channels, providing a mechanism by which current can be rapidly diminished during cellular repolarization. Furthermore, this study will be helpful to understand the functional diversity of BK channels contributed by different auxiliary β subunits.

Listeriolysin O secreted by Listeria monocytogenes into the host cell cytosol is degraded by the N-end rule pathway

The intracellular pathogen Listeria monocytogenes escapes from a phagosomal compartment into the cytosol by secreting the pore-forming cytolysin listeriolysin O (LLO). During the proliferation of L. monocytogenes bacteria in the mammalian cell cytosol, the secreted LLO is targeted for degradation by the ubiquitin system. We report here that LLO is a substrate of the ubiquitin-dependent N-end rule pathway, which recognizes LLO through its N-terminal Lys residue. Specifically, we demonstrated by reverse-genetic and pharmacological methods that LLO was targeted for degradation by the N-end rule pathway in reticulocyte extracts and mouse NIH 3T3 cells and after its secretion by intracellular bacteria into the mouse cell cytosol. Replacing the N-terminal Lys of LLO with a stabilizing residue such as Val increased the in vivo half-life of LLO but did not strongly affect the intracellular growth or virulence of L. monocytogenes. Nevertheless, this replacement decreased the virulence of L. monocytogenes by nearly twofold, suggesting that a destabilizing N-terminal residue of LLO may stem from positive selection during the evolution of this and related bacteria. A double mutant strain of L. monocytogenes in which upregulated secretion of LLO was combined with a stabilizing N-terminal residue was severely toxic to infected mammalian cells, resulting in reduced intracellular growth of bacteria and an approximately 100-fold-lower level of virulence. In summary, we showed that LLO is degraded by the N-end rule pathway and that the degradation of LLO can reduce the toxicity of L. monocytogenes during infection, a property of LLO that may have been selected for its positive effects on fitness during the evolution of L. monocytogenes.

A reversible form of lysine acetylation in the ER and Golgi lumen controls the molecular stabilization of BACE1

The lipid second messenger ceramide regulates the rate of beta cleavage of the Alzheimer's disease APP (amyloid precursor protein) by affecting the molecular stability of the beta secretase BACE1 (beta-site APP cleaving enzyme 1). Such an event is stimulated in the brain by the normal process of aging, and is under the control of the general aging programme mediated by the insulin-like growth factor 1 receptor. In the present study we report that BACE1 is acetylated on seven lysine residues of the N-terminal portion of the nascent protein. This process involves lysine acetylation in the lumen of the ER (endoplasmic reticulum) and is followed by deacetylation in the lumen of the Golgi apparatus, once the protein is fully mature. We also show that specific enzymatic activities acetylate (in the ER) and deacetylate (in the Golgi apparatus) the lysine residues. This process requires carrier-mediated translocation of acetyl-CoA into the ER lumen and is stimulated by ceramide. Site-directed mutagenesis indicates that lysine acetylation is necessary for nascent BACE1 to leave the ER and move ahead in the secretory pathway, and for the molecular stabilization of the protein.

Factors affecting guanine nucleotide binding to rat AMPA receptors

Glutamate receptors are competitively inhibited by guanine nucleotides. Insight into the physiological function of this inhibition would be greatly advanced if nucleotide binding could be eliminated through mutations without altering other aspects of receptor function, or if compounds were discovered that selectively prevent nucleotide binding. It was previously reported that a lysine in the chick kainate binding protein (cKBP) is specifically involved in guanine nucleotide binding. In the present study we mutated the equivalent lysine in the rat AMPA receptor subunit GluR1 flip to alanine (K445A) and assessed changes in nucleotide affinity from the displacement of [(3)H]fluorowillardiine. As in the cKBP, the affinity for nucleotides was greatly reduced while the binding affinity for agonists remained unchanged. The reduction in affinity was largest for GTP (factor of 5.8) and GDP (4.4) and minor for GMP and guanosine. This suggests that K445 is involved in stabilizing the second phosphate of the nucleotide. Given that bulkier analogs like GDP-fucose are also accommodated at this site, it seems likely that nucleotides bind in such a way that their phosphates project out of the cleft. In excised-patch recordings using short pulses of glutamate, the K445A mutation increased the EC(50) for the peak response 1.8-fold and accelerated desensitization and deactivation. This indicates that the effects of this mutation are not as specific as previously suggested. Efforts to selectively eliminate inhibition by nucleotides may therefore depend on mapping out further the docking site. In a first attempt using point mutations we ruled out several amino acids around the cleft as being involved in nucleotide binding. Also, the AMPA receptor modulator PPNDS which competitively inhibits nucleotide binding to purinergic receptors did not affect nucleotide inhibition, suggesting that there are major differences in the topography between purinergic and glutamate receptors. Thus new approaches, including crystallography, may be called for to identify residues uniquely involved in nucleotide binding.

Rate-limiting steps and role of active site Lys443 in the mechanism of carbapenam synthetase

Carbapenam synthetase (hereafter named CPS) catalyzes the formation of the beta-lactam ring in the biosynthetic pathway to (5R)-carbapen-2-em-3-carboxylate, the simplest of the carbapenem antibiotics. Kinetic studies showed remarkable tolerance to substrate stereochemistry in the turnover rate but did not distinguish between chemistry and a nonchemical step such as product release or conformational change as being rate-determining. Also, X-ray structural studies and modest sequence homology to beta-lactam synthetase, an enzyme that catalyzes the formation of a monocyclic beta-lactam ring in a similar ATP/Mg2+-dependent reaction, implicate K443 as an essential residue for substrate binding and intermediate stabilization. In these experiments, we use pH-rate profiles, deuterium solvent isotope effects, and solvent viscosity measurements to examine the rate-limiting step in this complex overall process of substrate adenylation and intramolecular ring formation. Mutagenesis and chemical rescue demonstrate that K443 is the general acid visible in the pH-rate profile of the wild-type CPS-catalyzed reaction. On the basis of these results, we propose a mechanism in which the rate-limiting step is beta-lactam ring formation coupled to a protein conformational change and underscore the role of K443 throughout the reaction.

A novel tripartite motif involved in aquaporin topogenesis, monomer folding and tetramerization

Aquaporin (AQP) folding in the endoplasmic reticulum is characterized by two distinct pathways of membrane insertion that arise from divergent residues within the second transmembrane segment. We now show that in AQP1 these residues (Asn49 and Lys51) interact with Asp185 at the C terminus of TM5 to form a polar, quaternary structural motif that influences multiple stages of folding. Asn49 and Asp185 form an intramolecular hydrogen bond needed for proper helical packing, monomer formation and function. In contrast, Lys51 interacts with Asp185 on an adjacent monomer to stabilize the AQP1 tetramer. Although these residues are unique to AQP1, they share a highly conserved architecture whose functional properties can be transferred to other family members. These findings suggest a general mechanism by which evolutionary divergence of membrane proteins can confer new functional properties via alternative folding pathways that give rise to a common final structure.

Max is acetylated by p300 at several nuclear localization residues

Max is a ubiquitous transcription factor with a bHLHZip [basic HLH (helix-loop-helix) leucine zipper] DNA-binding/dimerization domain and the central component of the Myc/Max/Mad transcription factor network that controls cell growth, proliferation, differentiation and apoptotic cell death in metazoans. Max is the obligatory DNA-binding and dimerization partner for all the bHLHZip regulators of the Myc/Max/Mad network, including the Myc family of oncoproteins and the Mad family of Myc antagonists, which recognize E-box DNA elements in the regulatory regions of target genes. Max lacks a transcription regulatory domain and is the only member of the network that efficiently homodimerizes. Binding of Max homodimers to E-box elements suppresses the transcription regulatory functions of its network partners and of other non-network E-box-binding regulators. In contrast with its highly regulated partners, Max is a constitutively expressed and phosphorylated protein. Phosphorylation is, however, the only Max post-translational modification identified so far. In the present study, we have analysed Max posttranslational modifications by MS. We have found that Max is acetylated at several lysine residues (Lys-57, Lys-144 and Lys-145) in mammalian cells. Max acetylation is stimulated by inhibitors of histone deacetylases and by overexpression of the p300 co-activator/HAT (histone acetyltransferase). The p300 HAT also directly acetylates Max in vitro at these three residues. Interestingly, the three Max residues acetylated in vivo and in vitro by p300 are important for Max nuclear localization and Max-mediated suppression of Myc transactivation. These results uncover novel post-translational modifications of Max and suggest the potential regulation of specific Max complexes by p300 and reversible acetylation.

Mechanism of dihydroneopterin aldolase: functional roles of the conserved active site glutamate and lysine residues

Dihydroneopterin aldolase (DHNA) catalyzes the conversion of 7,8-dihydroneopterin (DHNP) to 6-hydroxymethyl-7,8-dihydropterin (HP) in the folate biosynthetic pathway. There are four conserved active site residues at the active site, E22, Y54, E74, and K100 in Staphylococcus aureus DHNA (SaDHNA), corresponding to E21, Y53, E73, and K98, respectively, in Escherichia coli DHNA (EcDHNA). The functional roles of the conserved glutamate and lysine residues have been investigated by site-directed mutagenesis in this work. E22 and E74 of SaDHNA and E21, E73, and K98 of EcDHNA were replaced with alanine. K100 of SaDHNA was replaced with alanine and glutamine. The mutant proteins were characterized by equilibrium binding, stopped-flow binding, and steady-state kinetic analyses. For SaDHNA, none of the mutations except E74A caused dramatic changes in the affinities of the enzyme for the substrate or product analogues or the rate constants. The Kd values for SaE74A were estimated to be >3000 microM, suggesting that the Kd values of the mutant are at least 100 times those of the wild-type enzyme. For EcDHNA, the E73A mutation increased the Kd values for the substrate or product analogues neopterin (MP), monapterin (NP), and 6-hydroxypterin (HPO) by factors of 340, 160, and 5600, respectively, relative to those of the wild-type enzyme. The K98A mutation increased the Kd values for NP, MP, and HPO by factors of 14, 3.6, and 230, respectively. The E21A mutation increased the Kd values for NP and HPO by factors of 2.2 and 42, respectively, but decreased the Kd value for MP by a factor of 3.3. The E22 (E21) and K100 (K98) mutations decreased the kcat values by factors of 1.3-2 x 10(4). The E74 (E73) mutation decreased in the kcat values by factors of approximately 10. The results suggested that E74 of SaDHNA and E73 of EcDHNA are important for substrate binding, but their roles in catalysis are minor. In contrast, E22 and K100 of SaDHNA are important for catalysis, but their roles in substrate binding are minor. On the other hand, E21 and K98 of EcDHNA are important for both substrate binding and catalysis.

Characterization of the nuclear localization signal of high risk HPV16 E2 protein

The E2 protein of high risk human papillomavirus type 16 (HPV16) contains an amino-terminal (N) domain, a hinge (H) region and a carboxyl-terminal (C) DNA-binding domain. Using enhanced green fluorescent protein (EGFP) fusions with full length E2 and E2 domains in transfection assays in HeLa cells, we found that the C domain is responsible for the nuclear localization of E2 in vivo, whereas the N and H domains do not contain additional nuclear localization signals (NLSs). Deletion analysis of EGFP-E2 and EGFP-cE2 determined that the C domain contains an alpha helix cNLS that overlaps with the DNA-binding region. Mutational analysis revealed that the arginine and lysine residues in this cNLS are essential for nuclear localization of HPV16 E2. Interestingly, these basic amino acid residues are well conserved among the E2 proteins of BPV-1 and some high risk HPV types but not in the low risk HPV types, suggesting that there are differences between the NLSs and corresponding nuclear import pathways between these E2 proteins.

The Advanced Glycation End Product Nε-Carboxymethyllysine Is Not a Predictor of Cardiovascular Events and Renal Outcomes in Patients With Type 2 Diabetic Kidney Disease and Hypertension

BACKGROUND

Advanced glycation end products (AGEs) are implicated in the pathogenesis of vascular damage, especially in patients with diabetes and renal insufficiency. The oxidatively formed AGE N(epsilon)-carboxymethyllysine (CML) is thought to be a marker of oxidative stress.

METHODS

Four hundred fifty patients with type 2 diabetes and nephropathy from the Irbesartan in Diabetic Nephropathy Trial cohort (mean age, 58 +/- 8.2 years; 137 women, 313 men) with a mean glomerular filtration rate of 48.2 mL/min (0.80 mL/s; Modification of Diet in Renal Disease formula) were followed up for 2.6 years. Serum CML was measured by using an enzyme-linked immunosorbent assay. Relationships between CML levels, traditional risk factors, and cardiovascular and renal events were tested in Cox proportional hazards models.

RESULTS

Mean serum CML level was 599.9 +/- 276.0 ng/mL, and mean hemoglobin A1c level was 7.5% +/- 1.6%. One hundred forty-three first cardiovascular events occurred during follow-up; 74 patients died, 44 of cardiovascular causes. Final multivariate analysis showed age (relative risk [RR], 1.87; confidence interval [CI], 1.13 to 3.11; P = 0.016 for the highest compared with lowest quartile), history of prior cardiovascular events (RR, 1.96; CI, 1.35 to 2.85; P < 0.0005), and 24-hour urinary albumin-creatinine ratio (RR, 1.29; CI, 1.11 to 1.50 per doubling; P < 0.0005) to be independent risk factors for a first cardiovascular event, but not CML level. CML level also did not correlate significantly with renal outcome.

CONCLUSION

Serum CML level could not be identified as an independent risk factor for cardiovascular or renal outcomes in the examined population. This suggests that traditional risk factors might have a more important role for these end points or that other AGE compounds, as well as tissue AGE levels, might be of greater relevance compared with serum levels, which remains open to further study.

Mapping sequences required for nuclear localization and the transcriptional activation function of the Arabidopsis protein AINTEGUMENTA

The Arabidopsis thaliana floral development protein AINTEGUMENTA (ANT) is a member of a large family of DNA binding proteins (AP2/ERF family) that control plant growth and development in response to developmental or environmental signals. Transcriptional activation and/or repression activities have been demonstrated for several members of this protein family. We have used fusions between ANT and the GAL4 DNA binding domain to identify an 80 amino acid sequence important for the transcriptional activation function of ANT. This region shows similarity to transcriptional activation domains in other proteins, as it is rich in Ser/Thr, Gln/Asn, and acidic amino acids. We also demonstrate that ANT can activate gene expression in Arabidopsis plants through binding to a DNA sequence corresponding to an in vitro determined ANT binding site. Finally, we show that ANT is nuclear localized and that the sequence KKKR (amino acids 252-255) is required for nuclear localization of the protein.

Inhibition of MHC Class II Expression and Immune Responses by c-MIR

We previously reported a novel E3 ubiquitin ligase (E3), designated as c-MIR, which targets B7-2 to lysosomal degradation and down-regulates the B7-2 surface expression through ubiquitination of its cytoplasmic tail. B7-2 is well known as a costimulatory molecule for Ag presentation, suggesting that the manipulation of c-MIR expression modulates immune responses in vivo. To examine this hypothesis, we generated genetically modified mice in which c-MIR was expressed under an invariant chain (Ii) promoter. Dendritic cells derived from genetically engineered mice showed low ability to present Ags. In addition, these mice showed resistance to the onset of experimental autoimmune encephalomyelitis and an impaired development of CD4 T cells in the thymus and the periphery. These findings led us to conclude that MHC class II (MHC II) is an additional target for c-MIR. Indeed, forced expression of c-MIR in several B cell lines down-regulated the surface expression of MHC II, and down-regulation was found to depend on the presence of a single lysine residue in the cytoplasmic tail of the I-A beta-chain. In a reconstitution system using 293T cells, we found that the lysine residue at position 225 in the I-A beta-chain was ubiquitinated by c-MIR. To our knowledge, c-MIR is the first example of an E3 that is capable of inhibiting MHC II expression. Our findings suggest that c-MIR might potently regulate immune responses in vivo.

Lysine-63-linked ubiquitination is required for endolysosomal degradation of class I molecules

MHC class I molecules display peptides from endogenous and viral proteins for immunosurveillance by cytotoxic T lymphocytes (CTL). The importance of the class I pathway is emphasised by the remarkable strategies employed by different viruses to downregulate surface class I and avoid CTL recognition. The K3 gene product from Kaposi's sarcoma-associated herpesvirus (KSHV) is a viral ubiquitin E3 ligase which ubiquitinates and degrades cell surface MHC class I molecules. We now show that modification of K3-associated class I by lysine-63-linked polyubiquitin chains is necessary for their efficient endocytosis and endolysosomal degradation and present three lines of evidence that monoubiquitination of class I molecules provides an inefficient internalisation signal. This lysine-63-linked polyubiquitination requires both UbcH5b/c and Ubc13-conjugating enzymes for initiating mono- and subsequent polyubiquitination of class I, and the clathrin-dependent internalisation is mediated by the epsin endocytic adaptor. Our results explain how lysine-63-linked polyubiquitination leads to degradation by an endolysosomal pathway and demonstrate a novel mechanism for endocytosis and endolysosomal degradation of class I, which may be applicable to other receptors.

Lysine methylation and ‘signaling memory’

A combination of various post-translational modifications regulates the formation of signaling networks in both the nucleus and the cytosol. Of these, lysine methylation provides a relatively stable marker on histones and contributes to the formation of a distinct pattern of histone-dependent gene regulation ('transcriptional memory'). Thus far, lysine methylation was considered to be nucleus specific; however, recent findings indicate that lysine methylation contributes to receptor-mediated signal transduction in the cytosol.

An amino-terminal lysine residue of rat connexin40 that is required for spermine block

Spermine blocks connexin40 (Cx40) gap junctions, and two cytoplasmic amino-terminal domain glutamate residues are essential for this inhibitory activity. To further examine the molecular basis for block, we mutated a portion of a basic amino acid (HKH) motif on the Cx40 amino-terminal domain. Replacement of the Cx40 H15 + K16 residues with the Q15 + A16 sequence native to spermine-insensitive connexin43 (Cx43) gap junctions increased the equilibrium dissociation constant (K(d)) and reduced the maximum inhibition by spermine. The corresponding electrical distance (delta) approximation was decreased by about 50%. The transjunctional voltage (V(j))-dependent gating of homotypic Cx40 H15Q + K16A mutant gap junctions was also significantly reduced. The minimum normalized steady-state junctional conductance (G(min)) increased from 0.17 to 0.72, with an increase in the half-inactivation voltage from 48 to 60 mV. However, the unitary junctional conductance (gamma(j); 160 pS) was only slightly altered, and the relative cation/anion conductance and permeability ratios were unchanged from wild-type Cx40 gap junction channels. The relative K(+)/Cl(-) permeability (P(K)/P(Cl)) ratio increased from six to ten when [KCl] was reduced to 25% of normal. These data suggest that the HKH motif at positions 15-17 is important to the conformational structure of the putative voltage sensor and spermine receptor of Cx40, without causing significant alteration of the electrostatic surface charge potentials that contribute to the ion selectivity of this gap junction channel.

Structure–Sweetness Relationship in Egg White Lysozyme: Role of Lysine and Arginine Residues on the Elicitation of Lysozyme Sweetness

Lysozyme is one of the sweet-tasting proteins. To clarify the structure-sweetness relationship and the basicity-sweetness relationship in lysozyme, we have generated lysozyme mutants with Pichia systems. Alanine substitution of lysine residues demonstrated that two out of six lysine residues, Lys13 and Lys96, are required for lysozyme sweetness, while the remaining four lysine residues do not play a significant role in the perception of sweetness. Arginine substitution of lysine residues revealed that the basicity, but not the shape, of the side chain plays a significant role in sweetness. Single alanine substitutions of arginine residues showed that three arginine residues, Arg14, Arg21, and Arg73, play significant roles in lysozyme sweetness, whereas Arg45, Arg68, Arg125 and chemical modification by 1,2-cyclohexanedione did not affect sweetness. From investigation of the charge-specific mutations, we found that the basicity of a broad surface region formed by five positively charged residues, Lys13, Lys96, Arg14, Arg21, and Arg73, is required for lysozyme sweetness. Differences in the threshold values among sweet-tasting proteins might be caused by the broadness and/or the density of charged residues on the protein surface.

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.