2 research outputs found
Correlative Cryogenic Spectromicroscopy to Investigate Selenium Bioreduction Products
Accurate
mapping of the composition and structure of minerals and
associated biological materials is critical in geomicrobiology and
environmental research. Here, we have developed an apparatus that
allows the correlation of cryogenic transmission electron microscopy
(cryo-TEM) and synchrotron hard X-ray microprobe (SHXM) data sets
to precisely determine the distribution, valence state, and structure
of selenium in biofilms sampled from a contaminated aquifer near Rifle,
CO. Results were replicated in the laboratory via anaerobic selenate-reducing
enrichment cultures. 16S rRNA analyses of field-derived biofilm indicated
the dominance of Betaproteobacteria from the Comamonadaceae family
and uncultivated members of the Simplicispira genus. The major product in field and culture-derived biofilms is
∼25–300 nm red amorphous Se<sup>0</sup> aggregates of
colloidal nanoparticles. Correlative analyses of the cultures provided
direct evidence for the microbial dissimilatory reduction of SeÂ(VI)
to SeÂ(IV) to Se<sup>0</sup>. Extended X-ray absorption fine-structure
spectroscopy showed red amorphous Se<sup>0</sup> with a first shell
Se–Se interatomic distance of 2.339 ± 0.003 Å. Complementary
scanning transmission X-ray microscopy revealed that these aggregates
are strongly associated with a protein-rich biofilm matrix. These
findings have important implications for predicting the stability
and mobility of Se bioremediation products and understanding of Se
biogeochemical cycling. The approach, involving the correlation of
cryo-SHXM and cryo-TEM data sets from the same specimen area, is broadly
applicable to biological and environmental samples
Modulation of p300/CBP Acetylation of Nucleosomes by Bromodomain Ligand I‑CBP112
The
histone acetyltransferase (HAT) enzymes p300 and CBP are closely
related paralogs that serve as transcriptional coactivators and have
been found to be dysregulated in cancer and other diseases. p300/CBP
is a multidomain protein and possesses a highly conserved bromodomain
that has been shown to bind acetylated Lys residues in both proteins
and various small molecules, including I-CBP112 and CBP30. Here we
show that the ligand I-CBP112 can stimulate nucleosome acetylation
up to 3-fold while CBP30 does not. Activation of p300/CBP by I-CBP112
is not observed with the isolated histone H3 substrate but requires
a nucleosome substrate. I-CBP112 does not impact nucleosome acetylation
by the isolated p300 HAT domain, and the effects of I-CBP112 on p300/CBP
can be neutralized by CBP30, suggesting that I-CBP112 likely allosterically
activates p300/CBP through bromodomain interactions. Using mass spectrometry
and Western blots, we have found that I-CBP112 particularly stimulates
acetylation of Lys18 of histone H3 (H3K18) in nucleosomes, an established <i>in vivo</i> site of p300/CBP. In addition, we show that I-CBP112
enhances H3K18 acetylation in acute leukemia and prostate cancer cells
in a concentration range commensurate with its antiproliferative effects.
Our findings extend the known pharmacology of bromodomain ligands
in the regulation of p300/CBP and suggest a novel approach to modulating
histone acetylation in cancer