39 research outputs found
VIPP2 interacts with VIPP1 and HSP22E/F at chloroplast membranes and modulates a retrograde signal for HSP22E/F gene expression
VIPP proteins aid thylakoid biogenesis and membrane maintenance in cyanobacteria, algae, and plants. Some members of the Chlorophyceae contain two VIPP paralogs termed VIPP1 and VIPP2, which originate from an early gene duplication event during the evolution of green algae. VIPP2 is barely expressed under nonstress conditions but accumulates in cells exposed to high light intensities or H2O2, during recovery from heat stress, and in mutants with defective integration (alb3.1) or translocation (secA) of thylakoid membrane proteins. Recombinant VIPP2 forms rod-like structures in vitro and shows a strong affinity for phosphatidylinositol phosphate. Under stress conditions, >70% of VIPP2 is present in membrane fractions and localizes to chloroplast membranes. A vipp2 knock-out mutant displays no growth phenotypes and no defects in the biogenesis or repair of photosystem II. However, after exposure to high light intensities, the vipp2 mutant accumulates less HSP22E/F and more LHCSR3 protein and transcript. This suggests that VIPP2 modulates a retrograde signal for the expression of nuclear genes HSP22E/F and LHCSR3. Immunoprecipitation of VIPP2 from solubilized cells and membrane-enriched fractions revealed major interactions with VIPP1 and minor interactions with HSP22E/F. Our data support a distinct role of VIPP2 in sensing and coping with chloroplast membrane stress
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Working group 3: What are and how do we measure the pros and cons of existing approaches?
WG3 discussed both the pros and cons of existing schemes as well as metrics to measure relative advantages and disadvantages. We first provide a list of the current operational techniques and their respective advantages and disadvantages that were discussed in the WG. We do not claim
that the list is complete, and we note that the pros and cons are neither exhaustive nor quantitative. Nevertheless, it may be useful to note the WG’s consensus on the general
advantages and disadvantages of the most commonly-used schemes. We then list our recommendations for evaluating model uncertainty schemes. At the end is a short list pertaining to recommendations for further development of methods to represent model uncertainty
A fundamental catalytic difference between zinc and manganese dependent enzymes revealed in a bacterial isatin hydrolase
The catalytic mechanism of the cyclic amidohydrolase isatin hydrolase depends on a catalytically active manganese in the substrate-binding pocket. The Mn ion is bound by a motif also present in other metal dependent hydrolases like the bacterial kynurenine formamidase. The crystal structures of the isatin hydrolases from Labrenzia aggregata and Ralstonia solanacearum combined with activity assays allow for the identification of key determinants specific for the reaction mechanism. Active site residues central to the hydrolytic mechanism include a novel catalytic triad Asp-His-His supported by structural comparison and hybrid quantum mechanics/classical mechanics simulations. A hydrolytic mechanism for a Mn dependent amidohydrolases that disfavour Znas the primary catalytically active site metal proposed here is supported by these likely cases of convergent evolution. The work illustrates a fundamental difference in the substrate-binding mode between Mn dependent isatin hydrolase like enzymes in comparison with the vast number of Zn dependent enzymes
Effects of the integrated galactic IMF on the chemical evolution of the solar neighbourhood
The initial mass function determines the fraction of stars of different
intial mass born per stellar generation. In this paper, we test the effects of
the integrated galactic initial mass function (IGIMF) on the chemical evolution
of the solar neighbourhood. The IGIMF (Weidner & Kroupa 2005) is computed from
the combination of the stellar intial mass function (IMF), i.e. the mass
function of single star clusters, and the embedded cluster mass function, i.e.
a power law with index beta. By taking into account also the fact that the
maximum achievable stellar mass is a function of the total mass of the cluster,
the IGIMF becomes a time-varying IMF which depends on the star formation rate.
We applied this formalism to a chemical evolution model for the solar
neighbourhood and compared the results obtained by assuming three possible
values for beta with the results obtained by means of a standard, well-tested,
constant IMF. In general, a lower absolute value of beta implies a flatter
IGIMF, hence a larger number of massive stars and larger metal ejection rates.
This translates into higher type Ia and II supernova rates, higher mass
ejection rates from massive stars and a larger amount of gas available for star
formation, coupled with lower present-day stellar mass densities. (abridged) We
also discuss the importance of the present day stellar mass function (PDMF) in
providing a way to disentangle among various assumptions for beta. Our results
indicate that the model adopting the IGIMF computed with beta ~2 should be
considered the best since it allows us to reproduce the observed PDMF and to
account for most of the chemical evolution constraints considered in this work.Comment: 22 pages, 19 figure
Chemical enrichment of galaxy clusters from hydrodynamical simulations
We present cosmological hydrodynamical simulations of galaxy clusters aimed
at studying the process of metal enrichment of the intra--cluster medium (ICM).
These simulations have been performed by implementing a detailed model of
chemical evolution in the Tree-SPH \gd code. This model allows us to follow the
metal release from SNII, SNIa and AGB stars, by properly accounting for the
lifetimes of stars of different mass, as well as to change the stellar initial
mass function (IMF), the lifetime function and the stellar yields. As such, our
implementation of chemical evolution represents a powerful instrument to follow
the cosmic history of metal production. The simulations presented here have
been performed with the twofold aim of checking numerical effects, as well as
the impact of changing the model of chemical evolution and the efficiency of
stellar feedback.Comment: to appear on MNRA
The Formation of a Disk Galaxy within a Growing Dark Halo
We present a dynamical model for the formation and evolution of a massive
disk galaxy, within a growing dark halo whose mass evolves according to
cosmological simulations of structure formation. The galactic evolution is
simulated with a new 3D chemo-dynamical code, including dark matter, stars and
a multi-phase ISM. The simulations start at redshift z=4.85 with a small dark
halo in a LCDM universe and we follow the evolution until the present epoch.
The energy release by massive stars and SNe prevents a rapid collapse of the
baryonic matter and delays the maximum star formation until z=1. The galaxy
forms radially from inside-out and vertically from halo to disk. The first
galactic component that forms is the halo, followed by the bulge, the disk-halo
transition region, and the disk. At z=1, a bar begins to form which later turns
into a triaxial bulge. There is a pronounced deficiency of low-metallicity disk
stars due to pre-enrichment of the disk ISM with metal-rich gas from the bulge
and inner disk (G-dwarf problem). The mean rotation and the distribution of
orbital eccentricities for all stars as a function of metallicity are not very
different from those observed in the solar neighbourhood, showing that
homogeneous collapse models are oversimplified. The approach presented here
provides a detailed description of the formation and evolution of an isolated
disk galaxy in a LCDM universe, yielding new information about the kinematical
and chemical history of the stars and the ISM, but also about the evolution of
the luminosity, the colours and the morphology of disk galaxies.Comment: 23 pages, LaTeX, 18 figures, A&A accepted, a high resolution version
of the paper can be found at http://www.astro.unibas.ch/leute/ms.shtm
The chemical evolution of a Milky Way-like galaxy: the importance of a cosmologically motivated infall law
We aim at finding a cosmologically motivated infall law to understand if the
LambdaCDM cosmology can reproduce the main chemical characteristics of a Milky
Way-like spiral galaxy. In this work we test several different gas infall laws,
starting from that suggested in the two-infall model for the chemical evolution
of the Milky Way by Chiappini et al., but focusing on laws derived from
cosmological simulations which follows a concordance LambdaCDM cosmology. By
means of a detailed chemical evolution model for the solar vicinity, we study
the effects of the different gas infall laws on the abundance patterns and the
G-dwarf metallicity distribution. The cosmological gas infall law predicts two
main gas accretion episodes. By means of this cosmologically motivated infall
law, we study the star formation rate, the SNIa and SNII rate, the total amount
of gas and stars in the solar neighbourhood and the behaviour of several
chemical abundances. We find that the results of the two-infall model are fully
compatible with the evolution of the Milky Way with cosmological accretion
laws. A gas assembly history derived from a DM halo, compatible with the
formation of a late-type galaxy from the morphological point of view, can
produce chemical properties in agreement with the available observations.Comment: This paper has 26 pages, 19 figures and 5 table
Formation and Evolution of Early-Type Galaxies. III Star formation history as a function of mass and over-density
We investigate the influence of the initial proto-galaxies over-densities and
masses on their evolution, to understand whether the internal properties of the
proto-galactic haloes are sufficient to account for the varied properties of
the galactic populations. By means of fully hydrodynamical N-body simulations
performed with the code EvoL we produce twelve self-similar models of
early-type galaxies of different initial masses and over-densities, following
their evolution from z \geq 20 down to z \leq 1. The simulations include
radiative cooling, star formation, stellar energy feedback, a reionizing
photoheating background, and chemical enrichment of the ISM. We find a strong
correlation between the initial properties of the proto-haloes and their star
formation histories. Massive (10^13M\odot) haloes experience a single, intense
burst of star formation (with rates \geq 10^3M\odot/yr) at early epochs,
consistently with observations, with a less pronounced dependence on the
initial over-density; intermediate mass (10^11M\odot) haloes histories strongly
depend on their initial over-density, whereas small (10^9M\odot) haloes always
have fragmented histories, resulting in multiple stellar populations, due to
the "galactic breathing" phenomenon. The galaxy models have morphological,
structural and photometric properties comparable to real galaxies, often
closely matching the observed data; even though some disagreement is still
there, likely a consequence of some numerical choices. We conclude that
internal properties are essentially sufficient to explain many of the observed
features of early type galaxies, particularly the complicated and different
star formation histories shown by haloes of very different mass. In this
picture, nature seems to play the dominant role, whereas nurture has a
secondary importance.Comment: 27 pages, 25 figures, 5 table
Kinase and Phosphatase Cross-Talk at the Kinetochore
Multiple kinases and phosphatases act on the kinetochore to control chromosome segregation: Aurora B, Mps1, Bub1, Plk1, Cdk1, PP1, and PP2A-B56, have all been shown to regulate both kinetochore-microtubule attachments and the spindle assembly checkpoint. Given that so many kinases and phosphatases converge onto two key mitotic processes, it is perhaps not surprising to learn that they are, quite literally, entangled in cross-talk. Inhibition of any one of these enzymes produces secondary effects on all the others, which results in a complicated picture that is very difficult to interpret. This review aims to clarify this picture by first collating the direct effects of each enzyme into one overarching schematic of regulation at the Knl1/Mis12/Ndc80 (KMN) network (a major signaling hub at the outer kinetochore). This schematic will then be used to discuss the implications of the cross-talk that connects these enzymes; both in terms of why it may be needed to produce the right type of kinetochore signals and why it nevertheless complicates our interpretations about which enzymes control what processes. Finally, some general experimental approaches will be discussed that could help to characterize kinetochore signaling by dissociating the direct from indirect effect of kinase or phosphatase inhibition in vivo. Together, this review should provide a framework to help understand how a network of kinases and phosphatases cooperate to regulate two key mitotic processes
A Proton Wire and Water Channel Revealed in the Crystal Structure of Isatin Hydrolase
The high resolution crystal structures of isatin hydrolase from Labrenzia aggregata in the apo and the product state are described. These are the first structures of a functionally characterized metal-dependent hydrolase of this fold. Isatin hydrolase converts isatin to isatinate and belongs to a novel family of metalloenzymes that include the bacterial kynurenine formamidase. The product state, mimicked by bound thioisatinate, reveals a water molecule that bridges the thioisatinate to a proton wire in an adjacent water channel and thus allows the proton released by the reaction to escape only when the product is formed. The functional proton wire present in isatin hydrolase isoform b represents a unique catalytic feature common to all hydrolases is here trapped and visualized for the first time. The local molecular environment required to coordinate thioisatinate allows stronger and more confident identification of orthologous genes encoding isatin hydrolases within the prokaryotic kingdom. The isatin hydrolase orthologues found in human gut bacteria raise the question as to whether the indole-3-acetic acid degradation pathway is present in human gut flora