Structural Analyses of the Transient Receptor Potential Channels TRPV3 and TRPV6

Transient receptor potential (TRP) channels comprise a superfamily of cation-selective ion channels that are largely calcium (Ca2+) permeable and that play diverse physiological roles ranging from nociception in primary afferent neurons to the absorption of dietary Ca2+. The 28 mammalian TRP channels are categorized into 6 subfamilies. The vanilloid subfamily is named for its founding member, TRPV1, the capsaicin receptor, and has 6 members. TRPV1-4 are all heat sensitive ion channels whereas TRPV5 and TRPV6 are involved in renal Ca2+ reabsorption and Ca2+ absorption in the intestine, respectively. In our structural studies, we have focused on TRPV3 and TRPV6. TRPV6 is a highly Ca2+ selective TRP channel (PCa/PNa ~ 130) that functions in active Ca2+ absorption in the intestine. Its expression is upregulated by vitamin D and is, on the molecular level, regulated by PIP2 and calmodulin (CaM). Previously, the structure of TRPV6 was solved using X-ray crystallography. Using the crystal structure, a negatively charged extracellular vestibule was identified and anomalous diffraction was used to identify ion binding sites in the pore. Also, at the top of the selectivity filter, four aspartates were identified that coordinate Ca2+ entering the pore and confer to TRPV6 its selectivity for Ca2+. However, only the structure of the rat orthologue was solved and only in the closed, apo state. We used cryo-electron microscopy (cryo-EM) to solve structures of the human orthologue of TRPV6 in the open and closed (we used the mutation R470E to close the channel) states. The closed-to-open TRPV6 transition is accompanied by the formation of short π-helices in the middle of the pore-lining S6 helices, which in turn results in their turning and a different set of residues facing the pore. Additionally, the formation of the π-helices results in kinking of the S6 helices, which further widens the pore. TRPV6 is constitutively active when expressed heterologously. In other words, the addition of external stimuli is not necessary for the activation of the channel. Therefore, its activity needs to be regulated to prevent toxic Ca2+ overload. One mechanism by which this occurs is through its regulation by CaM. CaM has been shown to bind TRPV6 and regulate its function, however, the way it binds to and regulates TRPV6 remained unknown. To uncover this mechanism, we solved the structure of TRPV6 bound to CaM. We found that CaM binds TRPV6 in a 1:1 stoichiometric ratio and that CaM directly blocks the TRPV6 pore by inserting a positively charged lysine into a tera-tryptophan cage at the bottom of the pore. As a result, the channel adopts an inactivated conformation; although the pore-lining S6 helices still contain local π-helices, they are pulled closer together, narrowing the pore and further blocking it with hydrophobic side chains. We have also conducted studies of TRPV3. Unlike TRPV6, TRPV3 is a heat-activated vanilloid TRP channel. TRPV3 is expressed highly in keratinocytes where it has been implicated in wound healing and maintenance of the skin barrier, and in the regulation of hair growth. We solved the structure of apo TRPV3 in a closed state, and the structure of a TRPV3 mutant bound to 2-APB in an open state. Like TRPV6, the opening of TRPV3 is accompanied by the formation of local π-helices in the middle of the pore-lining S6 helices. The formation of the π-helices results in the lining of the ion permeation pathway with a different set of residues, resulting in a largely negatively charged pathway. Unlike TRPV6, TRPV3 is only slightly selective for Ca2+ and correspondingly, during gating state transitions, rearrangements were not only observed only in its pore-lining helices, but also in the cytosolic domain and the selectivity filter. Based on a comparison of our structures, we proposed a model of TRPV3 regulation by 2-APB. Together, our studies provide insight into the regulatory and gating mechanisms of the vanilloid subtype TRP channels and can provide the foundation for future studies

Impact of an improved neutrino energy estimate on outflows in neutron star merger simulations

Binary neutron star mergers are promising sources of gravitational waves for ground-based detectors such as Advanced LIGO. Neutron-rich material ejected by these mergers may also be the main source of r-process elements in the Universe, while radioactive decays in the ejecta can power bright electromagnetic post-merger signals. Neutrino-matter interactions play a critical role in the evolution of the composition of the ejected material, which significantly impacts the outcome of nucleosynthesis and the properties of the associated electromagnetic signal. In this work, we present a simulation of a binary neutron star merger using an improved method for estimating the average neutrino energies in our energy-integrated neutrino transport scheme. These energy estimates are obtained by evolving the neutrino number density in addition to the neutrino energy and flux densities. We show that significant changes are observed in the composition of the polar ejecta when comparing our new results with earlier simulations in which the neutrino spectrum was assumed to be the same everywhere in optically thin regions. In particular, we find that material ejected in the polar regions is less neutron rich than previously estimated. Our new estimates of the composition of the polar ejecta make it more likely that the color and timescale of the electromagnetic signal depend on the orientation of the binary with respect to an observer's line-of-sight. These results also indicate that important observable properties of neutron star mergers are sensitive to the neutrino energy spectrum, and may need to be studied through simulations including a more accurate, energy-dependent neutrino transport scheme.Comment: 19p, 17 figures, Accepted by Phys.Rev.

The discursive construction of “native speaker” and “non-native speaker” English teacher identities in Japan

Over the last several years, teacher identity has become a prominent area of research in the fields of English Language Teaching (ELT) and applied linguistics. One aspect of teacher identity, that of “native speaker” and “non-native speaker” identity, has become especially prevalent. Building on Phillipson’s (1992) concept of linguistic imperialism, Holliday (2005, 2006) identified an ideology of native-speakerism in the ELT industry that marginalizes those teachers that are seen as being “non-native speakers” of English, whilst at the same time privileging “native speaker” teachers and Western teaching methodologies. Taking a poststructuralist approach to identity as something that is fluid, unfixed and discursively constructed, this study aims to identify how and by whom “native speaker” and “non-native speaker” identities are constructed, and how these constructions are either resisted or embraced by teachers. This exploration of identity construction was carried out using the methodology of linguistic ethnography (LE) in order to collect a variety of data at one research site in Eastern Japan. This data set included classroom observations, fieldnotes, teacher interviews, student interviews, photos and institutional online media. Once the data was collected, Membership Categorisation Analysis (MCA) and intersectionality were used as analytical tools. The study found that macro discourses in the Japanese context, as well as institutional processes were powerful forces in perpetuating native-speakerist discourses and ascribing identity labels. However, in self-identification and in interactions with students, the picture was found to be more nuanced, with a complex picture of identity construction emerging that questioned the binary nature of the “native speaker/non-native speaker” duality. This complexity rested on an understanding of the intersectional nature of identity construction, and the importance of taking into account the intersectionality of a variety of identity markers when researching language teacher identity

P4_1 Rendezvous With Rama: An analysis of the physics behind Arthur C. Clarke's science-fiction spaceship

This article investigates quantitatively the conditions described by a group of astronauts within a ship in the science-ction book Rendezvous with Rama by Arthur C. Clarke. It was found that the conditions would have allowed the astronauts to walk on the surface but breathing would be difficult

P4_4 The Lunar Recession

This article investigates the Moon's recession from the Earth. The semi-major axis at which the Moon will become tidally locked with the Earth is calculated, and is found to be 558,000 km. It was found that the period of the Earth-Moon system would be about 48 current days long at this time. Using the Moon's current rate of recession, it was estimated that this process would happen in about 4.6 Gyr

P4_2 Tidal forces in the solar system

This article investigates the tidal accelerations exerted by planets on orbiting moons. The tidal acceleration was calculated, in terms of the acceleration due to gravity at the planet's surface, for several planetary systems in the solar system. A plot was created which showed that for most planetary systems, the tidal acceleration varied inversely as the cube of the semi-major axis, as theory predicted for the Earth and Moon

Stepfathers' affinity-seeking with stepchildren, stepfather-stepchild relationship quality, marital quality, and stepfamily cohesion among stepfathers and mothers

Because of the potential stepparent-stepchild relationships have for tension and conflict, clinicians have identified the development of a positive stepparent-stepchild connection as one of the major tasks of stepfamily life. Stepparents often are advised to focus initially on developing friendships with stepchildren, or seeking affinity with them, particularly early in the life of the relationship. Both family systems theory and evolutionary theory suggest that stepparents’ affinity-seeking behaviors are related to the quality and functioning of other stepfamily dyads, such as couple relationships, and the whole stepfamily. We extend prior work on stepparents’ affinity seeking by including perceptions of both members of the stepcouple about affinity seeking, stepfather-stepchild conflicts, couple relationship quality, and stepfamily cohesion. Stepfathers and mothers from 234 stepcouples independently completed online surveys. After accounting for covariates (i.e., duration of mothers’ previous relationships, duration of the stepcouple relationship, focal child’s biological sex and age, number of children in the household, and mothers’ report of household income), stepfathers’ perceptions of affinity-seeking with the focal child significantly predicted both partners’ perceptions of stepfather-stepchild conflict, marital quality, marital confidence, and stepfamily cohesion. Mothers’ perceptions of stepfathers’ affinity-seeking were significantly related to her marital confidence and perceptions of stepfamily cohesion. Stepfathers’ perceptions of their affinity-seeking explained more variance in stepfathers’ and mothers’ outcomes than did mothers’ perceptions. The results suggest benefits associated with stepfather affinity-seeking—less conflict with stepchildren, better couple relationships, and closer stepfamily ties. Our findings provide evidence for encouraging stepparents to focus on building affinity with stepchildren

P4_3 Shrinking the Earth

This article investigates the energy requirements to compress the Earth to within 1 km. This was done using a model assuming the compression to be elastic, and another model estimating the energy to overcome the Coulomb repulsion between the constituent protons. The energies found were 3.1x1032 J and 8.3x1038 J for each model respectively. It was also shown that to compress the Earth to within 1125 km you would have to overcome electron and neutron degeneracy pressure, and if compressed to a radius of 9 mm, the Earth would be a black hole.