MOS2, a protein containing G-patch and KOW motifs, is essential for innate immunity in Arabidopsis thaliana

Innate immunity is critical for sensing and defending against microbial infections in multicellular organisms. In plants, disease resistance genes (R genes) play central roles in recognizing pathogens and initiating downstream defense cascades. Arabidopsis SNC1 encodes a TIR-NBS-LRR-type R protein with a similar structure to nucleotide binding oligomerization domain (Nod) proteins in animals. A point mutation in the region between the NBS and LRR of SNC1 results in constitutive activation of defense responses in the snc1 mutant. Here, we report the identification and characterization of mos2-1, a mutant suppressing the constitutive defense responses in snc1. Analysis of mos2 single mutants indicated that it is not only required for resistance specified by multiple R genes, but also for basal resistance. Map-based cloning of MOS2 revealed that it encodes a novel nuclear protein that contains one G-patch and two KOW domains and has homologs across the animal kingdom. The presence of both G-patch and KOW domains in the MOS2 protein suggests that it probably functions as an RNA binding protein critical for plant innate immunity. Our discovery on the biological functions of MOS2 will shed light on functions of the MOS2 homologs in animals, where they may also play important roles in innate immunity.     

Masting by Betula-species; applying the resource budget model to north European data sets

Masting, the intermittent production of large crops of flowers by a plant population, is a common feature among trees in boreal and temperate forests. The pollen of many broadleaved trees causes allergic diseases, which are major causes of increasing health-care costs in industrialised countries. As the prevalence and severity of allergic diseases are connected with the concentrations of airborne pollen, an universal model predicting the intensity of the coming flowering would be a valuable tool for pollen information services, and ultimately for allergic people and allergologists. We investigated whether a resource budget model created in Japan explains the fluctuations in the annual pollen sums of Betula-species in north European data sets (10–12 years at 4 sites, 20 years at 10 sites). Using the shorter data sets, the model explained 76–92% of the annual fluctuations at five study sites. Using the 20-year data set, the percentage for southern Finland was much lower, only 48%, compared with the 85% of the 12-year data set. The annual pollen sums have been higher during the 1990s than in the 1980s, which may explain the ineffectiveness of the model, while applied to the 20-year data set. Our results support the resource budget model: the masting of birch species is regulated by weather factors together with the system of resource allocation among years. The model can serve pollen information service. However, only the 10 most recent years should be used to avoid interference from trends in changing vegetation and/or climate.     

Functional properties of recombinant factor V mutated in a potential calcium-binding site

Activated coagulation factor V (FVa) is a cofactor of activated factor X (FXa) in prothrombin activation. FVa is composed of a light chain (LC) and a heavy chain (HC) that are noncovalently associated in a calcium-dependent manner. We constructed a recombinant FV Asp111Asn/Asp112Asn mutant (rFV-NN) to abolish calcium binding to a potential calcium-binding site in FVa in order to study the specific role of these residues in the expression of FVa activity. Whereas thrombin-activated recombinant FV wild type (rFV-wt) presented with stable FVa activity, incubation of rFV-NN with thrombin resulted in a temporary increase in FVa activity, which was rapidly lost upon prolonged incubation. Loss of FVa activity was most likely due to dissociation of HC and LC since, upon chromatography of rFVa-NN on a SP-Sepharose column, the HC did not bind significantly to the resin whereas the LC bound and could be eluted at high ionic strength. In contrast, rFVa-wt adhered to the column, and both the HC and LC coeluted at high ionic strength. In the presence of phospholipid vesicles, the loss of rFVa-NN activity was partially prevented by FXa, active site inhibited FXa, and prothombin in a dose-dependent manner. We conclude that the introduced amino acid substitutions result in a loss of the high-affinity (calcium-dependent) interaction of the HC and LC of FVa. We propose that the introduced substitutions disrupt the calcium-binding site in FV, thereby yielding a FV molecule that rapidly loses activity following thrombin-catalyzed activation most likely via dissociation of the HC and LC.     

One-electron oxidation of catecholamines generates free radicals with an in vitro toxicity correlating with their lifetime

One-electron oxidation of dopamine by ferricyanide generates a highly reactive free radical intermediate that inactivates the V-type H(+)-ATPase proton pump in catecholamine storage vesicles, i.e., the driving force in both the vesicular uptake and the storage of catecholamines, in a cell-free in vitro model system at pH 7.0. Electron paramagnetic resonance spectroscopy revealed that a radical with g=2.0045, formed by this oxidation, was relatively long-lived (t(1/2) obs=79 s at pH 6.5 and 25 degrees C). Experimental evidence is presented that the observed radical most likely represents dopamine semiquinone free radical, although an o-quinone free radical cannot be ruled out. Oxidation of noradrenaline and adrenaline by ferricyanide generated similar isotropic radicals, but of shorter half-lives (i.e., 43 and 5.3 s, respectively), and the efficacy of inactivation of the H(+)-ATPase correlated with the half-life of the respective catecholamine free radical (i.e., dopamine >noradrenaline>adrenaline). Thus, the generation of relatively long-lived semiquinone free radicals, although at low concentrations, in dopaminergic and noradrenergic neurons may represent a common mechanism of cytotoxicity linked to neurodegeneration of the respective neurons related to Parkinson disease.     

Tapping diversity lost in transformations--in vitro amplification of ligation reactions

Molecular evolution is a powerful means of engineering proteins. It usually requires the generation of a large recombinant DNA library of variants for cloning into a phage or plasmid vector, and the transformation of a host organism for expression and screening of the variant proteins. However, library size is often limited by the low yields of circular DNA and the poor transformation efficiencies of linear DNA. Here we have overcome this limitation by amplification of recombinant circular DNA molecules directly from ligation reactions. The amplification by bacteriophage Phi29 polymerase increased the number of transformants; thus from a nanogram-scale ligation of DNA fragments comprising two sub-libraries of variant antibody domains, we succeeded in amplifying a highly diverse and large combinatorial phage antibody library (>10(9) transformants in Escherichia coli and 10(5)-fold more transformants than without amplification). From the amplified library, but not from the smaller un-amplified library, we could isolate several antibody fragments against a target antigen. It appears that amplification of ligations with Phi29 polymerase can help recover clones and molecular diversity otherwise lost in the transformation step. A further feature of the method is the option of using PCR-amplified vectors for ligations.     

Circular dichroism and magnetic circular dichroism studies of the active site of p53R2 from human and mouse: iron binding and nature of the biferrous site relative to other ribonucleotide reductases

Ribonucleotide reductases (RNR) catalyze the rate-limiting step in the synthesis of deoxyribonucleotides from the corresponding ribonucleotides in the synthesis of DNA. Class I RNR has two subunits: R1 with the substrate binding and active site and R2 with a stable tyrosyl radical and diiron cluster. Biferrous R2 reacts with oxygen to form the tyrosyl radical needed for enzymatic activity. A novel R2 form, p53R2, is a 351-amino acid protein induced by the "tumor suppressor gene" p53. p53R2 has been studied using a combination of circular dichroism, magnetic circular dichroism, variable-temperature variable-field MCD, and EPR spectroscopies. The active site of biferrous p53R2 in both the human (hp53R2) and mouse (mp53R2) forms is found to have one five-coordinate and one four-coordinate iron, which are weakly antiferromagnetically coupled through mu-1,3-carboxylate bridges. These spectroscopic data are very similar to those of Escherichia coli R2, and mouse R2, with a stronger resemblance to data of the former. Titrations of apo-hp53R2 and apo-mp53R2 with Fe(II) were pursued for the purpose of comparing their metal binding affinities to those of other R2s. Both p53R2s were found to have a high affinity for Fe(II), which is different from that of mouse R2 and may reflect differences in the regulation of enzymatic activity, as p53R2 is mainly triggered during DNA repair. The difference in ferrous affinity between mammalian R2 and p53R2 suggests the possibility of specific inhibition of DNA precursor synthesis during cell division.     

Kinetics and activation requirements of contact-dependent immune suppression by human regulatory T cells

Naturally occurring regulatory T cells (Tregs) maintain self tolerance by dominant suppression of potentially self-reactive T cells in peripheral tissues. However, the activation requirements, the temporal aspects of the suppressive activity, and mode of action of human Tregs are subjects of controversy. In this study, we show that Tregs display significant variability in the suppressive activity ex vivo as 54% of healthy blood donors examined had fully suppressive Tregs spontaneously, whereas in the remaining donors, anti-CD3/CD2/CD28 stimulation was required for Treg suppressive activity. Furthermore, anti-CD3/CD2/CD28 stimulation for 6 h and subsequent fixation in paraformaldehyde rendered the Tregs fully suppressive in all donors. The fixation-resistant suppressive activity of Tregs operated in a contact-dependent manner that was not dependent on APCs, but could be fully obliterated by trypsin treatment, indicating that a cell surface protein is directly involved. By add-back of active, fixed Tregs at different time points after activation of responding T cells, the responder cells were susceptible to Treg-mediated immune suppression up to 24 h after stimulation. This defines a time window in which effector T cells are susceptible to Treg-mediated immune suppression. Lastly, we examined the effect of a set of signaling inhibitors that perturb effector T cell activation and found that none of the examined inhibitors affected Treg activation, indicating pathway redundancy or that Treg activation proceeds by signaling mechanisms distinct from those of effector T cells.     

Impact of IL28B-related single nucleotide polymorphisms on liver histopathology in chronic hepatitis C genotype 2 and 3

Background and Aims

Recently, several genome-wide association studies have revealed that single nucleotide polymorphisms (SNPs) in proximity to IL28B predict spontaneous clearance of HCV infection as well as outcome following peginterferon and ribavirin therapy among HCV genotype 1 infected patients. The present study aimed to evaluate the impact of IL28B SNP variability on liver histology in the context of a phase III treatment trial (NORDynamIC) for treatment-naïve patients with chronic HCV genotype 2 or 3 infection, where pretreatment liver biopsies were mandatory.

Methods

Three hundred and thirty-nine Caucasian patients had samples available for IL28B genotyping (rs12979860) of whom 314 had pretreatment liver biopsies that were evaluated using the Ishak protocol, allowing for detailed grading and staging of liver histopathology.

Results

IL28B CC_rs12979860 genotype in HCV genotype 3 infected patients was associated with higher ALT levels (p<0.0001), higher AST to platelet ratio index (APRI; p = 0.001), and higher baseline viral load (p<0.0001) as compared to patients with the CT or TT genotypes. Additionally the CC_rs12979860 genotype entailed more pronounced portal inflammation (p = 0.02) and steatosis (p = 0.03). None of these associations were noted among HCV genotype 2 infected patients.

Conclusion

This study shows that the CC_rs12979860 SNP is associated with more pronounced liver histopathology in patients chronically infected with HCV genotype 3, which may be secondary to higher viral load. The finding that IL28B variability did not impact on liver pathology or viral load among genotype 2 infected patients implies that IL28B may differentially regulate the course of genotype 2 and 3 infection.