The structural determination and characterization of molecules, namely proteins and enzymes, is crucial to gaining a better understanding of their role in different chemical and biological processes. ...The continuous technical developments in the experimental and computational resources of X-ray diffraction (XRD) and, more recently, cryogenic Electron Microscopy (cryo-EM) led to an enormous growth in the number of structures deposited in the Protein Data Bank (PDB). Bioinorganic chemistry arose as a relevant discipline in biology and therapeutics, with a massive number of studies reporting the effects of metal complexes on biological systems, with vanadium complexes being one of the relevant systems addressed. In this review, we focus on the interactions of vanadium compounds (VCs) with proteins. Several types of binding are established between VCs and proteins/enzymes. Considering that the V-species that bind may differ from those initially added, the mentioned structural techniques are pivotal to clarifying the nature and variety of interactions of VCs with proteins and to proposing the mechanisms involved either in enzymatic inhibition or catalysis. As such, we provide an account of the available structural information of VCs bound to proteins obtained by both XRD and/or cryo-EM, mainly exploring the more recent structures, particularly those containing organic-based vanadium complexes.
Abstract
The Hubble Space Telescope UV Legacy Survey of Galactic Globular Clusters (GCs) has investigated GCs and their stellar populations. In previous papers of this series we have introduced a ...pseudo two-colour diagram, or ‘chromosome map’ (ChM) that maximizes the separation between the multiple populations. We have identified two main classes of GCs: Type I, including ∼83 per cent of the objects, and Type II clusters. Both classes host two main groups of stars, referred to in this series as first (1G) and second generation (2G). Type II clusters host more complex ChMs, exhibiting two or more parallel sequences of 1G and 2G stars. We exploit spectroscopic elemental abundances from the literature to assign the chemical composition to the distinct populations as identified on the ChMs of 29 GCs. We find that stars in different regions of the ChM have different compositions: 1G stars share the same light-element content as field stars, while 2G stars are enhanced in N and Na and depleted in O. Stars with enhanced Al, as well as stars with depleted Mg, populate the extreme regions of the ChM. We investigate the intriguing colour spread among 1G stars observed in many Type I GCs, and find no evidence for internal variations in light elements among these stars, whereas either a ∼0.1 dex iron spread or a variation in He among 1G stars remains to be verified. In the attempt of analysing the global properties of the multiple-population phenomenon, we have constructed a universal ChM, which highlights that, though very variegate, the phenomenon has some common pattern among all the analysed GCs. The universal ChM reveals a tight connection with Na abundances, for which we have provided an empirical relation. The additional ChM sequences observed in Type II GCs are enhanced in metallicity and, in some cases, s-process elements. Omega Centauri can be classified as an extreme Type II GC, with a ChM displaying three main extended ‘streams’, each with its own variations in chemical abundances. One of the most noticeable differences is found between the lower and upper streams, with the latter, associated with higher He, being also shifted towards higher Fe and lower Li abundances. We publicly release the ChMs.
Asteroseismic constraints on K giants make it possible to infer radii, masses and ages of tens of thousands of field stars. Tests against independent estimates of these properties are however scarce, ...especially in the metal-poor regime. Here, we report the detection of solar-like oscillations in eight stars belonging to the red-giant branch (RGB) and red-horizontal branch (RHB) of the globular cluster M4. The detections were made in photometric observations from the K2 Mission during its Campaign 2. Making use of independent constraints on the distance, we estimate masses of the eight stars by utilizing different combinations of seismic and non-seismic inputs. When introducing a correction to the Δν scaling relation as suggested by stellar models, for RGB stars we find excellent agreement with the expected masses from isochrone fitting, and with a distance modulus derived using independent methods. The offset with respect to independent masses is lower, or comparable with, the uncertainties on the average RGB mass (4–10 per cent, depending on the combination of constraints used). Our results lend confidence to asteroseismic masses in the metal-poor regime. We note that a larger sample will be needed to allow more stringent tests to be made of systematic uncertainties in all the observables (both seismic and non-seismic), and to explore the properties of RHB stars, and of different populations in the cluster.
We present high-precision multiband photometry for the globular cluster (GC) M2. We combine the analysis of the photometric data obtained from the Hubble Space Telescope UV Legacy Survey of Galactic ...GCs GO-13297, with chemical abundances by Yong et al., and compare the photometry with models in order to analyse the multiple stellar sequences we identified in the colour–magnitude diagram. We find three main stellar components, composed of metal-poor, metal-intermediate, and metal-rich stars (hereafter referred to as population A, B, and C, respectively). The components A and B include stars with different s-process element abundances. They host six sub-populations with different light-element abundances, and exhibit an internal variation in helium up to ΔY ∼ 0.07 dex. In contrast with M22, another cluster characterized by the presence of populations with different metallicities, M2 contains a third stellar component, C, which shows neither evidence for sub-populations nor an internal spread in light-elements. Population C does not exhibit the typical photometric signatures that are associated with abundance variations of light elements produced by hydrogen burning at hot temperatures. We compare M2 with other GCs with intrinsic heavy-element variations and conclude that M2 resembles M22, but it includes an additional stellar component that makes it more similar to the central region of the Sagittarius galaxy, which hosts a GC (M54) and the nucleus of the Sagittarius galaxy itself.
We explain the multiple populations recently found in the ‘prototype’ globular cluster (GC) NGC 2808 in the framework of the asymptotic giant branch (AGB) scenario. The chemistry of the five – or ...more – populations is approximately consistent with a sequence of star formation events, starting after the Type II supernova epoch, lasting approximately until the time when the third dredge-up affects the AGB evolution (age ∼90–120 Myr), and ending when the Type Ia supernovae begin exploding in the cluster, eventually clearing it from the gas. The formation of the different populations requires episodes of star formation in AGB gas diluted with different amounts of pristine gas. In the nitrogen-rich, helium-normal population identified in NGC 2808 by the UV Legacy Survey of GCs, the nitrogen increase is due to the third dredge-up in the smallest mass AGB ejecta involved in the star formation of this population. The possibly iron-rich small population in NGC 2808 may be a result of contamination by a single Type Ia supernova. The NGC 2808 case is used to build a general framework to understand the variety of ‘second-generation’ stars observed in GCs. Cluster-to-cluster variations are ascribed to differences in the effects of the many processes and gas sources which may be involved in the formation of the second generation. We discuss an evolutionary scheme, based on pollution by delayed Type II supernovae, which accounts for the properties of s-Fe-anomalous clusters.
In most X-ray diffraction studies reported vanadate binds as a 5-coordinate moiety within the protein.
•Interactions of vanadium compounds with proteins are reviewed.•Structural and functional ...aspects of vanadium–protein interactions are discussed.•The interactions of vanadium ions with enzymes may imply interference at distinct levels.•Phosphate–vanadate physicochemical similarities are relevant in protein binding and inhibition.•Vanadate(IV) can also mimic phosphate.
Vanadium is an element ubiquitously present in our planet's crust and thus there are several organisms that use vanadium for activity or function of proteins. Examples are the vanadium-dependent haloperoxidases and the vanadium-containing nitrogenases. Some organisms that use vanadium have extremely efficient and selective protein-dependent systems for uptake and transport of vanadium and are able to accumulate high levels of vanadium from seawater, vanabins being a unique family of vanadium binding proteins found in ascidians involved in this process. For all of the systems a discussion regarding the role of the V-containing proteins is provided, mostly centered on structural aspects of the vanadium site and, when possible or relevant, relating this to the mechanisms operating. Phosphate is very important in biological systems and is involved in an extensive number of biological recognition and bio-catalytic systems. Vanadate(V) is able to inhibit many of the enzymes involved in these processes, such as ATPases, phosphatases, ribonucleases, phosphodiesterases, phosphoglucomutase and glucose-6-phosphatase, and it appears clear that this is closely related to the analogous physicochemical properties of vanadate and phosphate. The ability of vanadium to interfere with the metabolic processes involving Ca2+ and Mg2+, connected with its versatility to undergo changes in coordination geometry, allow V to influence the function of a large variety of phosphate-metabolizing enzymes and vanadate(V) salts and compounds have been frequently used either as inhibitors of these enzymes, or as probes to study the mechanisms of their reactions and catalytic cycle. In this review we give an overview of the many examples so far reported, also disclosing that vanadate(IV) may also have an equally efficient inhibiting effect. The prospective application of vanadium compounds as therapeutics has also been an important topic of research. How vanadium may be transported in blood and up-taken by cells are particularly relevant issues, this being mainly dependent on transferrin (and albumin) present in blood plasma. The thousands of studies reported on the effects of vanadium compounds reflect the complexity of the interactions occurring. Although it is not easy to anticipate/determine if a particular effect observed in a test tube or in vitro is also going to take place in vivo, it is clear that vanadium ions may interfere with many metabolic processes at many distinct levels. Emphasis is given on structural and functional aspects of vanadium–protein interactions relevant for vanadium binding and/or for clarification of role of the metal center in the reaction mechanisms. The additional knowledge that the presence of vanadium can change the action of a protein, other than simply inhibiting it, may also be important to understand how vanadium affects biological systems. This possibility, together with the vanadate–phosphate analogy further potentiates the belief that vanadium probably has relevant functions in living beings, which may involve interaction or incorporation of the metal ion and/or its compounds with several proteins.
We present CN and CH indices and Ca ii triplet metallicities for 34 giant stars and chemical abundances for 33 elements in 14 giants in the globular cluster M2. Assuming that the programme stars are ...cluster members, our analysis reveals (i) an extreme variation in CN and CH line strengths, (ii) a metallicity dispersion with a dominant peak at Fe/H ≈ −1.7 and smaller peaks at −1.5 and −1.0, (iii) star-to-star abundance variations and correlations for the light elements O, Na, Al and Si and (iv) a large (and possibly bimodal) distribution in the abundances of all elements produced mainly via the s-process in Solar system material. Following Roederer, Marino & Sneden, we define two groups of stars, ‘r + s’ and ‘r-only’, and subtract the average abundances of the latter from the former group to obtain an ‘s-process residual’. This s-process residual is remarkably similar to that found in M22 and in M4 despite the range in metallicity covered by these three systems. With recent studies identifying a double subgiant branch in M2 and a dispersion in Sr and Ba abundances, our spectroscopic analysis confirms that this globular cluster has experienced a complex formation history with similarities to M22, NGC 1851 and ω Centauri.
We present a general overview and the first results of the SUMO project (a SUrvey of Multiple pOpulations in Globular Clusters). The objective of this survey is the study of multiple stellar ...populations in the largest sample of globular clusters homogeneously analysed to date. To this aim we obtained high signal-to-noise (S/N > 50) photometry for main sequence stars with mass down to ∼0.5 M in a large sample of clusters using both archival and proprietary U, B, V and I data from ground-based telescopes.
In this paper, we focus on the occurrence of multiple stellar populations in 23 clusters. We define a new photometric index, c
U, B, I
= (U − B) − (B − I), which turns out to be very effective for identifying multiple sequences along the red giant branch (RGB). We found that in the V-c
U, B, I
diagram all clusters presented in this paper show broadened or multimodal RGBs, with the presence of two or more components. We found a direct connection with the chemical properties of different sequences, which display different abundances of light elements (O, Na, C, N and Al). The c
U, B, I
index is also a powerful tool for identifying distinct sequences of stars along the horizontal branch and, for the first time in the case of NGC 104 (47 Tuc), along the asymptotic giant branch. Our results demonstrate that (i) the presence of more than two stellar populations is a common feature amongst globular clusters, as already highlighted in previous work; (ii) multiple sequences with different chemical contents can be easily identified by using standard Johnson photometry obtained with ground-based facilities; (iii) in the study of globular cluster multiple stellar populations the c
U, B, I
index is an alternative to spectroscopy, and has the advantage of larger statistics.
Stars in open clusters are expected to share an identical abundance pattern. Establishing the level of chemical homogeneity in a given open cluster deserves further study as it is the basis of the ...concept of chemical tagging to unravel the history of the Milky Way. M67 is particularly interesting given its solar metallicity and age as well as being a dense cluster environment. We conducted a strictly line-by-line differential chemical abundance analysis of two solar twins in M67: M67-1194 and M67-1315. Stellar atmospheric parameters and elemental abundances were obtained with high precision using Keck/High Resolution Echelle Spectrometer spectra. M67-1194 is essentially identical to the Sun in terms of its stellar parameters. M67-1315 is warmer than M67-1194 by ≈150 K as well as slightly more metal-poor than M67-1194 by ≈0.05 dex. M67-1194 is also found to have identical chemical composition to the Sun, confirming its solar-twin nature. The abundance ratios X/Fe of M67-1315 are similar to the solar abundances for elements with atomic number Z ≤ 30, while most neutron-capture elements are enriched by ≈0.05 dex, which might be attributed to enrichment from a mixture of asymptotic giant branch ejecta and r-process material. The distinct chemical abundances for the neutron-capture elements in M67-1315 and the lower metallicity of this star compared to M67-1194, indicate that the stars in M67 are likely not chemically homogeneous. This poses a challenge for the concept of chemical tagging since it is based on the assumption of stars forming in the same star-forming aggregate.
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