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Similar Interactions (similar + interaction)
Selected AbstractsDELLA protein function in growth responses to canopy signalsTHE PLANT JOURNAL, Issue 1 2007Tanja Djakovic-Petrovic Summary Plants can sense neighbour competitors through light-quality signals and respond with shade-avoidance responses. These include increased shoot elongation, which enhances light capture and thus competitive power. Such plant,plant interactions therefore profoundly affect plant development in crowded populations. Shade-avoidance responses are tightly coordinated by interactions between light signals and hormones, with essential roles for the phytochrome B photoreceptor [sensing the red:far red (R:FR) ratio] and the hormone gibberellin (GA). The family of growth-suppressing DELLA proteins are targets for GA signalling and are proposed to integrate signals from other hormones. However, the importance of these regulators has not been studied in the ecologically relevant, complex realm of plant canopies. Here we show that DELLA abundance is regulated during growth responses to neighbours in dense Arabidopsis stands. This occurs in a R:FR-dependent manner in petioles, depends on GA, and matches the induction kinetics of petiole elongation. Similar interactions were observed in the growth response of seedling hypocotyls and are general for a second canopy signal, reduced blue light. Enhanced DELLA stability in the gai mutant inhibits shade-avoidance responses, indicating that DELLA proteins constrain shade-avoidance. However, using multiple DELLA knockout mutants, we show that the observed DELLA breakdown is not sufficient to induce shade-avoidance in petioles, but plays a more central role in hypocotyls. These data provide novel information on the regulation of shade-avoidance under ecologically important conditions, defining the importance of DELLA proteins and GA and unravelling the existence of GA- and DELLA-independent mechanisms. [source] The role of residues R97 and Y331 in modulating the pH optimum of an insect ,-glycosidase of family 1FEBS JOURNAL, Issue 24 2003Sandro R. Marana The activity of the digestive ,-glycosidase from Spodoptera frugiperda (Sf,gly50, pH optimum 6.2) depends on E399 (pKa = 4.9; catalytic nucleophile) and E187 (pKa = 7.5; catalytic proton donor). Homology modelling of the Sf,gly50 active site confirms that R97 and Y331 form hydrogen bonds with E399. Site-directed mutagenesis showed that the substitution of R97 by methionine or lysine increased the E399 pKa by 0.6 or 0.8 units, respectively, shifting the pH optima of these mutants to 6.5. The substitution of Y331 by phenylalanine increased the pKa of E399 and E187 by 0.7 and 1.6 units, respectively, and displaced the pH optimum to 7.0. From the observed ,pKa it was calculated that R97 and Y331 contribute 3.4 and 4.0 kJ·mol,1, respectively, to stabilization of the charged E399, thus enabling it to be the catalytic nucleophile. The substitution of E187 by D decreased the pKa of residue 187 by 0.5 units and shifted the pH optimum to 5.8, suggesting that an electrostatic repulsion between the deprotonated E399 and E187 may increase the pKa of E187, which then becomes the catalytic proton donor. In short the data showed that a network of noncovalent interactions among R97, Y331, E399 and E187 controls the Sf,gly50 pH optimum. As those residues are conserved among the family 1 ,-glycosidases, it is proposed here that similar interactions modulate the pH optimum of all family 1 ,-glycosidases. [source] Worms and malaria: noisy nuisances and silent benefitsPARASITE IMMUNOLOGY, Issue 7 2002Mathieu Nacher Summary The burden of malaria mortality has been a major evolutionary influence on human immunity. The selection of the most successful immune responses against malaria has been in populations concomitantly infected by intestinal helminths. Animal models have shown that coinfections with helminths and protozoa in the same host elicit a range of antagonist and synergistic interactions. Recent findings suggest similar interactions take place between helminths, Plasmodium falciparum and humans. However, as the threat of HIV and tuberculosis becomes a major selective force, what used to be a successful ecological system may now prove detrimental. Nevertheless, the understanding of the ecological forces at play may expose new intervention targets for malaria control, and give a new perspective on our shortcomings against the deadliest of human parasites. [source] Allele-specific genetic interactions between Mitf and Kit affect melanocyte developmentPIGMENT CELL & MELANOMA RESEARCH, Issue 3 2010Bin Wen Summary The tyrosine kinase receptor KIT and the transcription factor MITF, each required for melanocyte development, have been shown to interact functionally both in vitro and in vivo. In vitro, KIT signaling leads to MITF phosphorylation, affecting MITF activity and stability. In vivo, the presence of the Mitf,Mi-wh allele exacerbates the spotting phenotype associated with heterozygosity for Kit mutations. Here, we show that among a series of other Mitf alleles, only the recessive Mitf,mi-bws mimics the effect of Mitf,Mi-wh on Kit. Intriguingly, Mitf,mi-bws is characterized by a splice defect that leads to a reduction of RNAs containing MITF exon 2B which encodes serine-73, a serine phosphorylated upon KIT signaling. Nevertheless, other Mitf alleles that generally affect Mitf RNA levels, or carry a serine-73-to-alanine mutation that specifically reduces exon 2B-containing RNAs, do not show similar interactions with Kit in vivo. We conclude that the recessive Mitf,mi-bws is a complex allele that can display a semi-dominant effect when present in a Kit -sensitized background. We suggest that human disease variability may equally be due to complex, allele-specific interactions between different genes. [source] Four new species of the myrmecophile Diplocotes Westwood (Coleoptera: Ptinidae) from Queensland and South AustraliaAUSTRALIAN JOURNAL OF ENTOMOLOGY, Issue 2 2008Karen L Bell Abstract, Four new species of the Australian ptinid genus Diplocotes are described. Two of these species are from the dry tropical and subtropical areas of northern and central Queensland, while the other two are from the arid areas of South Australia. While the four new species described here have not been observed with ants in the field, the species of this genus are known to be myrmecophilous, and similar interactions may occur between the new species and their host ants. Additionally, many characters are shared with other unrelated myrmecophilous species, and may be convergent adaptations to the ant-associated lifestyle. [source] The 1.35,Å resolution structure of the phosphatase domain of the suppressor of T-cell receptor signaling protein in complex with sulfateACTA CRYSTALLOGRAPHICA SECTION F (ELECTRONIC), Issue 6 2010Jean Jakoncic The suppressor of T-cell signaling (Sts) proteins are multidomain proteins that negatively regulate the signaling of membrane-bound receptors, including the T-cell receptor (TCR) and the epidermal growth-factor receptor (EGFR). They contain at their C-terminus a 2H-phosphatase homology (PGM) domain that is responsible for their protein tyrosine phosphatase activity. Here, the crystal structure of the phosphatase domain of Sts-1, Sts-1PGM, was determined at pH 4.6. The asymmetric unit contains two independent molecules and each active site is occupied by a sulfate ion. Each sulfate is located at the phosphate-binding site and makes similar interactions with the catalytic residues. The structure suggests an explanation for the lower Michaelis,Menten constants at acidic pH. [source] Structures of BIR domains from human NAIP and cIAP2ACTA CRYSTALLOGRAPHICA SECTION F (ELECTRONIC), Issue 11 2009Maria Dolores Herman The inhibitor of apoptosis (IAP) family of proteins contains key modulators of apoptosis and inflammation that interact with caspases through baculovirus IAP-repeat (BIR) domains. Overexpression of IAP proteins frequently occurs in cancer cells, thus counteracting the activated apoptotic program. The IAP proteins have therefore emerged as promising targets for cancer therapy. In this work, X-ray crystallography was used to determine the first structures of BIR domains from human NAIP and cIAP2. Both structures harbour an N-terminal tetrapeptide in the conserved peptide-binding groove. The structures reveal that these two proteins bind the tetrapeptides in a similar mode as do other BIR domains. Detailed interactions are described for the P1,,P4, side chains of the peptide, providing a structural basis for peptide-specific recognition. An arginine side chain in the P3, position reveals favourable interactions with its hydrophobic moiety in the binding pocket, while hydrophobic residues in the P2, and P4, pockets make similar interactions to those seen in other BIR domain,peptide complexes. The structures also reveal how a serine in the P1, position is accommodated in the binding pockets of NAIP and cIAP2. In addition to shedding light on the specificity determinants of these two proteins, the structures should now also provide a framework for future structure-based work targeting these proteins. [source] In vivo and in vitro Interactions between Human Colon Carcinoma Cells and Hepatic Stellate CellsCANCER SCIENCE, Issue 12 2000Sadatoshi Shimizu Stromal reaction is important for the growth of cancer both in primary and metastatic sites. To demonstrate this reaction during the hepatic metastasis of human colon carcinoma, we histologically investigated alterations to the distribution and phenotype of hepatic stellate cells (HSCs), the only mesenchymal cells in the liver parenchyma, using a nude mouse model. Intrasplenically injected colon carcinoma LM-H3 cells migrated into the space of Disse and underwent proliferation, in close association with hepatocytes and HSCs, at 2 days. At 14 days, HSCs were accumulated around the tumor mass and expressed ,-smooth muscle actin, a marker for HSC activation. We next investigated in vitro the growth factors involved in the interactions between LM-H3 cells and HSCs. Conditioned medium of rat HSCs which underwent culture-induced activation contained platelet-derived growth factor (PDGF)-AB, hepatocyte growth factor (HGF) and transforming growth factor (TGF),, and could augment LM-H3-cell proliferation and migration. Neutralizing antibodies against PDGF-AA and PDGF-BB and those against PDGF-BB and HGF inhibited proliferation and migration, respectively, of LM-H3 cells, whereas antibody against TGF-, had no effect. LM-H3 cells expressed PDGF receptors-, and -, and c-met. Conditioned medium of LM-H3 cells contained PDGF-AB, and could enhance HSC proliferation and migration. This augmenting effect was suppressed by treatment with anti-PDGF-AB antibody. The present study has demonstrated that bidirectional interactions involving PDGF and HGF take place in vitro between colon carcinoma cells and HSCs, raising the possibility that similar interactions might be involved in the stromal reaction during hepatic metastasis. [source] | ||||||||||||||||