The study of cooperative ligand binding to multimeric proteins aims to explain complex cooperative binding phenomena using concepts derived from ideal binding isotherms. The purpose of such efforts is the dissection of the cooperative binding isotherm into its interacting components, a result with a clear mechanistic value. Historically, cooperative binding is usually quantified using the Hill coefficient, $$\hbox {n}_\mathrm{H}$$nH, defined as the slope of the Hill plot at 50 % saturation. It was previously shown that the slope of the Hill plot throughout the titration is equal to the ratio of the binding variance in the system under study, to the binding variance of a reference non-interacting system. In the present contribution, this leads to a broader approach towards quantifying cooperativity, which empirically links cooperativity to the ensemble average of the subunit interaction energy. The resulting equations can be used to derive average differential subunit interaction energies directly from experimental binding isotherms. Combined with recent experimental advances in assessing binding distributions in multimeric proteins, these equations can also be used to calculate individual subunit interaction energies for specific n-ligated protein species.
By discussing two literary texts by immigrants from Europe in America, Isaac Bashevis Singer’s Enemies, a Love Story (1966) and Edgar Hilsenrath’s Fuck America (Bronskys Geständnis, 1980), the essays examines the Holocaust survivors’ gradual subversion of pre-determined national, religious, and communal identities. In each of the texts, the urban environment has a double and seemingly contradictory effect on the survivors’ lives: it is an obstacle but also an opportunity. The multiplying sounds, languages, faces, and buildings seem at first to be a threat to the protagonists’ existence but later on provide the means for their radical liberation. As an eternal outsider, the survivor’s past experience correlates and is constantly juxtaposed to his current urban life. This juxtaposition creates a desire for anonymity, as an immediate reaction to the identity which was foisted upon each protagonist during the war in Europe. Singer’s Herman Broder and Hilsenrath’s Jakob Bronsky are literary models that offer, in their grim life stories, a new set of human relationships, personal behavioral characteristics, and private day to day procedures that correlate to the deviant city’s schizoid features. My discussion of the novels relies on Michel de Certeau’s The Practice of Everyday Life. De Certeau’s observations regarding the ordinary mundane procedures that constitute the urban “pedestrian” text illuminate the way in which the protagonists’ stories incorporate, rather than ignore or resolve, their contradictory, fragmentary, and unsystematic components.
June 2016: Noam Gil is currently teaching in the English and American Studies Department at Tel Aviv University. He has recently submitted his Doctorate Dissertation on Holocaust Survivors in Jewish American Fiction.
Honey bee colonies, foraging predominantly on a single pollen source, may encounter nutritional deficits. In the present study, we examined the nutritional resilience of honey bee colonies, testing whether foragers shift their foraging effort towards resources that complement a nutritional deficit. Eight honey bee colonies were kept in screened enclosures and fed for 1 week a pollen substitute diet deficient in a particular essential amino acid. Foragers were subsequently tested for a preference between the same diet previously fed, a different diet that was similarly deficient, or a diet that complemented the deficiency. Foragers preferred the complementary diet over the same or similar diets. Appetitive conditioning tests showed that bees were able to discriminate also between the same and similar diets. Overall, our results support the hypothesis that honey bees prefer dietary diversity, and that they do not just include novel sources but specifically target nutritionally complementary ones. Whereas we specifically focused on deficiencies in essential amino acids, we cannot rule out that bees were also complementing correlated imbalances in other nutrients, most notably essential fatty acids. The ability of honey bees to counter deficient nutrition contributes to the mechanisms which social insects use to sustain homeostasis at the colony level.
Leaf development serves as a model for plant developmental flexibility. Flexible balancing of morphogenesis and differentiation during leaf development results in a large diversity of leaf forms, both between different species and within the same species. This diversity is particularly evident in compound leaves. Hormones are prominent regulators of leaf development. Here we discuss some of the roles of plant hormones and the cross-talk between different hormones in tomato compound-leaf development.
Natural Killer (NK) cells are critical in the defense against viruses in general and against influenza in particular. We previously demonstrated that the activating NK cell receptor NKp46 is involved in the killing of influenza-virus infected cells through its interaction with viral hemagglutinin (HA). Furthermore, the recognition by NKp46 and consequent elimination of influenza infected cells were determined to be sialic-acid dependent. Here, we show that the human co-activating receptors 2B4 and NTB-A directly recognize the viral HA protein and co-stimulate killing by NK cells. We demonstrate that the 2B4/NTB-A-HA interactions require the sialylation of these receptors, and we identified the binding sites mediating these interactions. We also show that the virus counters these interactions through its neuraminidase (NA) protein. These results emphasize the critical role played by NK cells in eliminating influenza, a significant cause of worldwide morbidity and mortality.
: Mesenchymal stem cells (MSCs) are currently the most established cells for skeletal tissue engineering and regeneration; however, their availability and capability of self-renewal are limited. Recent discoveries of somatic cell reprogramming may be used to overcome these challenges. We hypothesized that induced pluripotent stem cells (iPSCs) that were differentiated into MSCs could be used for bone regeneration. Short-term exposure of embryoid bodies to transforming growth factor-beta was used to direct iPSCs toward MSC differentiation. During this process, two types of iPSC-derived MSCs (iMSCs) were identified: early (aiMSCs) and late (tiMSCs) outgrowing cells. The transition of iPSCs toward MSCs was documented using MSC marker flow cytometry. Both types of iMSCs differentiated in vitro in response to osteogenic or adipogenic supplements. The results of quantitative assays showed that both cell types retained their multidifferentiation potential, although aiMSCs demonstrated higher osteogenic potential than tiMSCs and bone marrow-derived MSCs (BM-MSCs). Ectopic injections of BMP6-overexpressing tiMSCs produced no or limited bone formation, whereas similar injections of BMP6-overexpressing aiMSCs resulted in substantial bone formation. Upon orthotopic injection into radial defects, all three cell types regenerated bone and contributed to defect repair. In conclusion, MSCs can be derived from iPSCs and exhibit self-renewal without tumorigenic ability. Compared with BM-MSCs, aiMSCs acquire more of a stem cell phenotype, whereas tiMSCs acquire more of a differentiated osteoblast phenotype, which aids bone regeneration but does not allow the cells to induce ectopic bone formation (even when triggered by bone morphogenetic proteins), unless in an orthotopic site of bone fracture. SIGNIFICANCE: Mesenchymal stem cells (MSCs) are currently the most established cells for skeletal tissue engineering and regeneration of various skeletal conditions; however, availability of autologous MSCs is very limited. This study demonstrates a new method to differentiate human fibroblast-derived induced pluripotent stem cells (iPSCs) to cells with MSC properties, which we comprehensively characterized including differentiation potential and transcriptomic analysis. We showed that these iPS-derived MSCs are able to regenerate nonunion bone defects in mice more efficiently than bone marrow-derived human MSCs when overexpressing BMP6 using a nonviral transfection method.
