Functional determination of calcium-binding sites required for the activation of inositol 1,4,5-trisphosphate receptors

Inositol 1,4,5-trisphosphate receptors (IP3Rs) initiate a diverse array of physiological responses by carefully orchestrating intracellular calcium (Ca2+) signals in response to various external cues. Notably, IP3R channel activity is determined by several obligatory factors, including IP3, Ca2+, and ATP. The critical basic amino acid residues in the N-terminal IP3-binding core (IBC) region that facilitate IP3 binding are well characterized. In contrast, the residues conferring regulation by Ca2+ have yet to be ascertained. Using comparative structural analysis of Ca2+-binding sites identified in two main families of intracellular Ca2+-release channels, ryanodine receptors (RyRs) and IP3Rs, we identified putative acidic residues coordinating Ca2+ in the cytosolic calcium sensor region in IP3Rs. We determined the consequences of substituting putative Ca2+ binding, acidic residues in IP3R family members. We show that the agonist-induced Ca2+ release, single-channel open probability (P0), and Ca2+ sensitivities are markedly altered when the negative charge on the conserved acidic side chain residues is neutralized. Remarkably, neutralizing the negatively charged side chain on two of the residues individually in the putative Ca2+-binding pocket shifted the Ca2+ required to activate IP3R to higher concentrations, indicating that these residues likely are a component of the Ca2+ activation site in IP3R. Taken together, our findings indicate that Ca2+ binding to a well-conserved activation site is a common underlying mechanism resulting in increased channel activity shared by IP3Rs and RyRs

Characterizing Aeolian Sediment Transport on Mars Using In Situ Observations

Wind is one of the major drivers of geomorphic change on terrestrial bodies throughout our solar system. Yet, our understanding of how wind-driven, or aeolian, processes operate under different planetary regimes has been limited by what we can study here on Earth. Prior to robotic exploration of Mars, terrestrially-derived theories predicted that tenuous Martian winds would rarely, if ever, be able to mobilize surface sediment. Once spacecraft arrived at Mars, it became clear that wind was not only a major geomorphic agent, it was likely the most dominant in the planet’s recent geologic history, especially given the paucity of other active surface processes (e.g., hydrology, plate tectonics, or volcanism). Repeat “change detection” images acquired from orbital and landed cameras have provided extensive evidence of ongoing aeolian activity, despite low predicted and measured winds. Here we describe change detection experiments conducted from the Mars Science Laboratory (MSL) Curiosity rover and InSight lander on Mars. These imaging campaigns have provided key information on the nature of aeolian activity occurring under modern Martian climatic conditions. In Gale crater, change detection images have demonstrated a strong seasonality in wind, with a relatively quiescent period during the first half of the year followed by a windy period between Ls 180 – 360◦, consistent with the strong winds predicted in and around southern summer. During this season, formative winds result from a combination of enhanced Hadley flows and thermally driven slope winds, which generate strong northeasterlies at the location of the rover; over long time periods, these flows have caused significant deflation across Aeolis Palus, and have facilitated the development of large dune fields downwind at the base of Mount Sharp. Late in 2018, the InSight lander touched down five hundred kilometers north of Gale crater, in the volcanic plains of Elysium Planitia. Concurrent imaging and atmospheric monitoring have suggested that, at this location, the modern surface is relatively stable and that ongoing aeolian activity may be limited to dust entrainment during convective vortex events. Cumulatively, change detection experiments have provided an unprecedented look at active Martian surface processes, and have shed light on some of the fundamental differences that may exist between Earth and Mars

A Search for RR Lyrae Stars in Segue 2 and Segue 3

We present an extensive search for RR Lyrae (RRL) stars in and around the ultra-faint Milky Way companions Segue 2 and Segue 3. The former (MV = –2.5) appears to be an extremely faint dwarf galaxy companion of the Milky Way. The latter (MV = 0.0) is among the faintest star clusters known. We use B and V band time-series imaging obtained at the WIYN 0.9 m telescope at Kitt Peak National Observatory to search for RRL in these objects. In our Segue 2 observations, we present a previously unknown fundamental mode (RRab) RRL star with a period of P ab = 0.748 days. With this measurement, we revisit the inverse correlation between P ab and [Fe/H] established in the literature for Milky Way dwarf galaxies and their RRL. In this context, the long period of Segue 2\u27s RRab star as well as the known significant spread in metallicity in this dwarf galaxy are consistent with the observed trend in P ab and [Fe/H]. We derive the first robust distance to Segue 2, using both its RRab star and spectroscopically confirmed blue horizontal branch stars. Using [Fe/H] = –2.16 and –2.44 dex, we find and kpc; assuming [Fe/H] = –2.257 dex, we find d BHB = 34.4 ± 2.6 kpc. Although no RRL were present in the Segue 3 field, we found a candidate eclipsing binary star system