抗原变异可使得多种致病微生物易于逃避宿主免疫应答。表达在感染红细胞表面的恶性疟原虫红细胞表面蛋白1（PfPMP1）与感染红细胞、内皮细胞、树突状细胞以及胎盘的单个或多个受体作用，在黏附及免疫逃避中起关键的作用。每个单倍体基因组var基因家族编码约60种成员，通过启动转录不同的var基因变异体为抗原变异提供了分子基础。

疟原虫var基因转换速率变化导致抗原变异[英]／Paul H, Robert P, Christodoulou Z, et al//Proc Natl Acad Sci U S A

Organismal life encounters reactive oxidants from internal metabolism and environmental toxicant exposure. Reactive oxygen and nitrogen species cause oxidative stress and are traditionally viewed as being harmful. On the other hand, controlled production of oxidants in normal cells serves useful purposes to regulate signaling pathways. Reactive oxidants are counterbalanced by complex antioxidant defense systems regulated by a web of pathways to ensure that the response to oxidants is adequate for the body's needs. A recurrent theme in oxidant signaling and antioxidant defense is reactive cysteine thiol–based redox signaling. The nuclear factor erythroid 2–related factor 2 (Nrf2) is an emerging regulator of cellular resistance to oxidants. Nrf2 controls the basal and induced expression of an array of antioxidant response element–dependent genes to regulate the physiological and pathophysiological outcomes of oxidant exposure. This review discusses the impact of Nrf2 on oxidative stress and toxicity and how...

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Role of nrf2 in oxidative stress and toxicity.

Reactive oxygen species (ROS) have been shown to be toxic but also function as signalling molecules. This biological paradox underlies mechanisms that are important for the integrity and fitness of living organisms and their ageing. The pathways that regulate ROS homeostasis are crucial for mitigating the toxicity of ROS and provide strong evidence about specificity in ROS signalling. By taking advantage of the chemistry of ROS, highly specific mechanisms have evolved that form the basis of oxidant scavenging and ROS signalling systems.

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ROS as signalling molecules: mechanisms that generate specificity in ROS homeostasis

Impaired selective turnover of p62 by autophagy causes severe liver injury accompanied by the formation of p62-positive inclusions and upregulation of detoxifying enzymes. These phenotypes correspond closely to the pathological conditions seen in human liver diseases, including alcoholic hepatitis and hepatocellular carcinoma. However, the molecular mechanisms and pathophysiological processes in these events are still unknown. Here we report the identification of a novel regulatory mechanism by p62 of the transcription factor Nrf2, whose target genes include antioxidant proteins and detoxification enzymes. p62 interacts with the Nrf2-binding site on Keap1, a component of Cullin-3-type ubiquitin ligase for Nrf2. Thus, an overproduction of p62 or a deficiency in autophagy competes with the interaction between Nrf2 and Keap1, resulting in stabilization of Nrf2 and transcriptional activation of Nrf2 target genes. Our findings indicate that the pathological process associated with p62 accumulation results in hyperactivation of Nrf2 and delineates unexpected roles of selective autophagy in controlling the transcription of cellular defence enzyme genes.

The selective autophagy substrate p62 activates the stress responsive transcription factor Nrf2 through inactivation of Keap1

The Nrf2 regulatory network provides an interface between redox and intermediary metabolism

The expression of the phase 2 detoxification enzymes and antioxidant proteins is induced at the transcriptional level by Nrf2 and negatively regulated at the posttranslational level by Keap1 through protein-protein interactions with and subsequent proteolysis of Nrf2. We found that the Neh2 domain of Nrf2 is an intrinsically disordered but biologically active regulatory domain containing a 33-residue central alpha-helix followed by a mini antiparallel beta-sheet. Isothermal calorimetry analysis indicated that one Neh2 molecule interacts with two molecules of Keap1 via two binding sites, the stronger binding ETGE motif and the weaker binding DLG motif. Nuclear magnetic resonance titration study showed that these two motifs of the Neh2 domain bind to an overlapping site on the bottom surface of the beta-propeller structure of Keap1. In contrast, the central alpha-helix of the Neh2 domain does not have any observable affinity to Keap1, suggesting that this region may serve as a bridge connecting the two motifs for the association with the two beta-propeller structures of a dimer of Keap1. Based on these observations, we propose that Keap1 recruits Nrf2 by the ETGE motif and that the DLG motif of the Neh2 domain locks its lysine-rich central alpha-helix in a correct position to benefit ubiquitin signaling.

Keap1 recruits Neh2 through binding to ETGE and DLG motifs: characterization of the two-site molecular recognition model.

A new strategy is described for the production of peptides enriched with stable isotopes Peptides of interest are expressed in Escherichia coli (E coli) cells as recombinant fusion proteins with Saccharomyces cerevisiae ubiquitin This method yields as much as 30-100 mg/l of isotope-enriched fusion proteins in minimal media A decahistidine tag attached to the N-terminus of ubiquitin enables a one-step purification of the fusion protein via Ni(2+)-chelating affinity chromatography The ubiquitin moiety is then easily and specifically cleaved off by a protease, yeast ubiquitin hydrolase Since this enzyme is also expressed at a high level in E coli cells and can be purified in one step, the presented strategy has an advantage in view of costs over others that use commercially available proteases In addition, since ubiquitin fusion proteins easily refold, the fusion protein can be expressed either in a soluble form or as inclusion bodies This flexibility enables us to prepare peptides that are unstable in a soluble state in E coli cells As an example, the expression and the uniform stable isotope enrichment with 15N and/or 13C are described for mastoparan-X, a tetradecapeptide known to activate GTP-binding regulatory proteins An amide group at the C-terminus of this peptide can also be formed by our method The presented system is considered powerful for the stable isotope enrichment of short peptides with proton resonances that are too severely overlapped to be analyzed solely by proton NMR

A new general method for the biosynthesis of stable isotope-enriched peptides using a decahistidine-tagged ubiquitin fusion system: an application to the production of mastoparan-X uniformly enriched with 15N and 15N/13C.

The Maf family proteins, which constitute a subgroup of basic region-leucine zipper (bZIP) proteins, function as transcriptional regulators of cellular differentiation. Together with the basic region, the Maf extended homology region (EHR), conserved only within the Maf family, defines the DNA binding specific to Mafs. Here we present the first NMR-derived structure of the DNA-binding domain (residues 1-76) of MafG, which contains the EHR and the basic region. The structure consists of three alpha-helices and resembles the fold of the DNA-binding domain of Skn-1, a developmental transcription factor of Caenorhabditis elegans. The structural similarity between MafG and Skn-1 enables us to propose a possible mechanism by which Maf family proteins recognize their consensus DNA sequences.

Solution structure of the DNA-binding domain of MafG.

Mastoparans, a family of tetradecapeptides from wasp venom, have been used as convenient low molecular weight models of receptors coupled to GTP-binding regulatory proteins (G proteins) for the understanding of the interaction between G proteins and receptors. Sukumar and Higashijima have analyzed the conformation of mastoparan-X (MP-X) bound to the G protein α-subunit using proton two-dimensional transferred nuclear Overhauser effect (TRNOE) spectroscopy [Sukumar, M., and Higashijima, T. (1992) J. Biol. Chem., 267, 21421−21424]. The resultant structure, however, was not well-defined due to severe overlap of peptide proton resonances. To determine the G protein-bound conformation of MP-X in detail, we have analyzed this interaction by heteronuclear multidimensional TRNOE experiments of MP-X uniformly enriched with 15N and/or 13C. By solving the overlap problem, we were able to determine the precise conformation of MP-X bound to Gi1α:  the peptide adopts an amphiphilic α-helix from Trp3 to C-terminal Leu14...

G protein-bound conformation of mastoparan-X: heteronuclear multidimensional transferred nuclear overhauser effect analysis of peptide uniformly enriched with 13C and 15N.

Hepatitis C virus (HCV) has been recognized as a major cause of chronic liver diseases worldwide It has been suggested that HCV infects not only hepatocytes but also mononuclear lymphocytes including B cells that express the CD81 molecule, a putative HCV receptor HCV infection of B cells is the likely cause of B-cell dysregulation disorders such as mixed cryoglobulinemia, rheumatoid factor production, and B-cell lymphoproliferative disorders that may evolve into non-Hodgkin's lymphoma (NHL) Epidemiological data indicate an association between HCV chronic infection and the occurrence of B-cell NHL, suggesting that chronic HCV infection is associated at least in part with B-cell lymphomagenesis In this paper, we aim to provide an overview of recent literature, including our own, to elucidate a possible role of HCV chronic infection in B-cell lymphomagenesis

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Hideki Kusunoki

Papers

Keap1 recruits Neh2 through binding to ETGE and DLG motifs: characterization of the two-site molecular recognition model.

A new general method for the biosynthesis of stable isotope-enriched peptides using a decahistidine-tagged ubiquitin fusion system: an application to the production of mastoparan-X uniformly enriched with 15N and 15N/13C.

Solution structure of the DNA-binding domain of MafG.

G protein-bound conformation of mastoparan-X: heteronuclear multidimensional transferred nuclear overhauser effect analysis of peptide uniformly enriched with 13C and 15N.

HCV Infection and B-Cell Lymphomagenesis