Bridging-hydride influence on the electronic structure of an [FeFe] hydrogenase active-site model complex revealed by XAES-DFT

[[abstract]]Two crystallized [FeFe] hydrogenase model complexes, 1 = (μ-pdt)[Fe(CO)2(PMe3)]2 (pdt = SC1H2C2H2C3H2S), and their bridging-hydride (Hy) derivative, [1Hy]+++ = [(μ-H)(μ-pdt)[Fe(CO)2 (PMe3)]2]+ (BF4−), were studied by Fe K-edge X-ray absorption and emission spectroscopy, supported by density functional theory. Structural changes in [1Hy]+++ compared to 1 involved small bond elongations (<0.03 Å) and more octahedral Fe geometries; the Fe–H bond at Fe1 (closer to pdt-C2) was [similar]0.03 Å longer than that at Fe2. Analyses of (1) pre-edge absorption spectra (core-to-valence transitions), (2) Kβ1,3, Kβ′, and Kβ2,5 emission spectra (valence-to-core transitions), and (3) resonant inelastic X-ray scattering data (valence-to-valence transitions) for resonant and non-resonant excitation and respective spectral simulations indicated the following: (1) the mean Fe oxidation state was similar in both complexes, due to electron density transfer from the ligands to Hy in [1Hy]+++. Fe 1s→3d transitions remained at similar energies whereas delocalization of carbonyl AOs onto Fe and significant Hy-contributions to MOs caused an [similar]0.7 eV up-shift of Fe1s→(CO)s,p transitions in [1Hy]+++. Fed-levels were delocalized over Fe1 and Fe2 and degeneracies biased to Oh–Fe1 and C4v–Fe2 states for 1, but to Oh–Fe1,2 states for [1Hy]+++. (2) Electron-pairing of formal Fe(d7) ions in low-spin states in both complexes and a higher effective spin count for [1Hy]+++ were suggested by comparison with iron reference compounds. Electronic decays from Fe d and ligand s,p MOs and spectral contributions from Hys,p→1s transitions even revealed limited site-selectivity for detection of Fe1 or Fe2 in [1Hy]+++. The HOMO/LUMO energy gap for 1 was estimated as 3.0 ± 0.5 eV. (3) For [1Hy]+++ compared to 1, increased Fed (x2 − y2) − (z2) energy differences ([similar]0.5 eV to [similar]0.9 eV) and Fed→d transition energies ([similar]2.9 eV to [similar]3.7 eV) were assigned. These results reveal the specific impact of Hy-binding on the electronic structure of diiron compounds and provide guidelines for a directed search of hydride species in hydrogenases.[[notice]]補正完畢[[journaltype]]國外[[ispeerreviewed]]Y[[booktype]]紙本[[booktype]]電子版[[countrycodes]]GB

Selective Translational Control and Its Role in Cancer

Cancer initiation is hallmarked by the inability of cells to properly control their proliferation and growth. Tumor suppressor genes often function to restrain improper cell growth and division, as well as to stimulate cell death under certain circumstances to keep our cells in proper balance and prevent cellular transformation. The alternative reading frame (ARF) tumor suppressor is critical in this sense. In response to hyperproliferative stimuli, ARF acts as a key regulator of ribosome biogenesis and induces cell cycle arrest through p53-dependent and -independent mechanisms. The main objectives of my dissertation research are to identify novel molecular targets of ARF that contribute to its tumor surveillance activities, to characterize the mechanisms through which this regulation occurs, and to understand how these targets abrogate/promote tumorigenesis. Defining new regulatory pathways linked to ARF function will further our insight into how cells evade these safeguards during cellular transformation. Cancer cells require robust protein synthesis, and in many cases, cancer initiation is accompanied by an increase in the translational efficiency of a select group of mRNAs. At the onset of my dissertation research, it had been demonstrated that ARF not only negatively modulates ribosome maturation, in part through repressing DDX5 activity, but also that loss of ARF alters the population of ribosome-bound transcripts in a selective manner. However, it was not known whether ARF was able to regulate other proteins associated with ribosome biogenesis to further limit cell growth in the presence of oncogenic cues. Moreover, the mechanisms driving this sophisticated translational repression network in the absence of ARF remained unclear. Given DDX5\u27s known interaction with the microprocessor component, Drosha, a protein previously linked with rRNA processing, I hypothesized that Drosha may be repressed by ARF in a similar manner to DDX5. I also hypothesized that miRNAs, a class of non-coding RNAs commonly associated with blocking the translation of select mRNAs, may serve as downstream effector molecules in ARF-mediated tumor suppression and that loss of Arf prompts a change in the miRNA signature of a cell ultimately promoting cell growth and proliferation. The data presented in this dissertation reveals that Drosha protein expression is enhanced in the absence of ARF and that this induction relies solely on the increased translation of existing Drosha mRNAs. Through this regulatory network, ARF is able to restrict rRNA synthesis at the processing stage and protect cells from oncogene-induced transformation as elevated Drosha expression is critical in maintaining RasV12-induced cellular transformation. A closer examination of Drosha in the context of human breast cancer demonstrated that its locus is frequently amplified and that the resulting heighted Drosha expression confers a proliferative and tumorigenic advantage for certain cells. Lastly, loss of Arf impacts mature miRNA expression, albeit not globally, and restoration of a subset of these miRNAs partially restores growth control and protection from neoplastic transformation even in the absence of ARF. Taken together these data suggest novel and critical roles of miRNAs and Drosha in ARF tumor suppression and the involvement of the latter in facilitating mammary tumorigenesis

ARF tumor suppression in the nucleolus

AbstractSince its discovery close to twenty years ago, the ARF tumor suppressor has played a pivotal role in the field of cancer biology. Elucidating ARF's basal physiological function in the cell has been the focal interest of numerous laboratories throughout the world for many years. Our current understanding of ARF is constantly evolving to include novel frameworks for conceptualizing the regulation of this critical tumor suppressor. As a result of this complexity, there is great need to broaden our understanding of the intricacies governing the biology of the ARF tumor suppressor. The ARF tumor suppressor is a key sensor of signals that instruct a cell to grow and proliferate and is appropriately localized in nucleoli to limit these processes. This article is part of a Special Issue entitled: Role of the Nucleolus in Human Disease