5 research outputs found
Superconductivity in single crystals of a quasi-one dimensional infinite chain cuprate SrCaCuO at 90 K
Although there is no complete theory of high temperature superconductivity,
the importance of CuO planes in cuprate superconductors is confirmed from
both theory and experiments. Strong Coulomb repulsion between electrons on the
CuO plane makes the resultant electron system highly correlated and a
difficult problem to solve since exact solutions of many-body Hamiltonian in
two dimensions do not exist. If however, superconductivity can arise in
structures having chains rather than planes and having a high critical
temperature, then the high temperature superconductivity problem could become
more tractable since exact solutions in one dimension do exist. In this paper,
we report the observation of bulk superconductivity in single crystals of a
cuprate SrCaCuO at very high critical temperature, T, of
90 K whose structure reveals the presence of infinite double chains of
Cu-O-Cu-O instead of CuO planes, thus, ensuring quasi-one dimensional
superconductivity. Bulk superconducting behaviour was observed in \textit{dc}
magnetisation, \textit{ac} susceptibility as well as resistance measurements.
The observation of bulk superconductivity in SrCaCuO having
chains of Cu-O-Cu-O rather than planes of CuO at a high T of 90 K is
expected to profoundly impact our understanding of high temperature
superconductivity.Comment: 15 pages, 4 figure
Disturbed Expression of Splicing Factors in Renal Cancer Affects Alternative Splicing of Apoptosis Regulators, Oncogenes, and Tumor Suppressors
BACKGROUND: Clear cell renal cell carcinoma (ccRCC) is the most common type of renal cancer. One of the processes disturbed in this cancer type is alternative splicing, although phenomena underlying these disturbances remain unknown. Alternative splicing consists of selective removal of introns and joining of residual exons of the primary transcript, to produce mRNA molecules of different sequence. Splicing aberrations may lead to tumoral transformation due to synthesis of impaired splice variants with oncogenic potential. In this paper we hypothesized that disturbed alternative splicing in ccRCC may result from improper expression of splicing factors, mediators of splicing reactions. METHODOLOGY/PRINCIPAL FINDINGS: Using real-time PCR and Western-blot analysis we analyzed expression of seven splicing factors belonging to SR proteins family (SF2/ASF, SC35, SRp20, SRp75, SRp40, SRp55 and 9G8), and one non-SR factor, hnRNP A1 (heterogeneous nuclear ribonucleoprotein A1) in 38 pairs of tumor-control ccRCC samples. Moreover, we analyzed splicing patterns of five genes involved in carcinogenesis and partially regulated by analyzed splicing factors: RON, CEACAM1, Rac1, Caspase-9, and GLI1. CONCLUSIONS/SIGNIFICANCE: We found that the mRNA expression of splicing factors was disturbed in tumors when compared to paired controls, similarly as levels of SF2/ASF and hnRNP A1 proteins. The correlation coefficients between expression levels of specific splicing factors were increased in tumor samples. Moreover, alternative splicing of five analyzed genes was also disturbed in ccRCC samples and splicing pattern of two of them, Caspase-9 and CEACAM1 correlated with expression of SF2/ASF in tumors. We conclude that disturbed expression of splicing factors in ccRCC may possibly lead to impaired alternative splicing of genes regulating tumor growth and this way contribute to the process of carcinogenesis
Conservation of Apolipoprotein A‑I’s Central Domain Structural Elements upon Lipid Association on Different High-Density Lipoprotein Subclasses
The antiatherogenic properties of
apolipoprotein A-I (apoA-I) are
derived, in part, from lipidation-state-dependent structural elements
that manifest at different stages of apoA-I’s progression from
lipid-free protein to spherical high-density lipoprotein (HDL). Previously,
we reported the structure of apoA-I’s N-terminus on reconstituted
HDLs (rHDLs) of different sizes. We have now investigated at the single-residue
level the conformational adaptations of three regions in the central
domain of apoA-I (residues 119–124, 139–144, and 164–170)
upon apoA-I lipid binding and HDL formation. An important function
associated with these residues of apoA-I is the activation of lecithin:cholesterol
acyltransferase (LCAT), the enzyme responsible for catalyzing HDL
maturation. Structural examination was performed by site-directed
tryptophan fluorescence and spin-label electron paramagnetic resonance
spectroscopies for both the lipid-free protein and rHDL particles
7.8, 8.4, and 9.6 nm in diameter. The two methods provide complementary
information about residue side chain mobility and molecular accessibility,
as well as the polarity of the local environment at the targeted positions.
The modulation of these biophysical parameters yielded new insight
into the importance of structural elements in the central domain of
apoA-I. In particular, we determined that the loosely lipid-associated
structure of residues 134–145 is conserved in all rHDL particles.
Truncation of this region completely abolished LCAT activation but
did not significantly affect rHDL size, reaffirming the important
role of this structural element in HDL function
Conservation of Apolipoprotein A-I’s Central Domain Structural Elements upon Lipid Association on Different High-Density Lipoprotein Subclasses
The antiatherogenic properties of apolipoprotein A-I (apoA-I) are derived, in part, from lipidation-state-dependent structural elements that manifest at different stages of apoA-I's progression from lipid-free protein to spherical high-density lipoprotein (HDL). Previously, we reported the structure of apoA-I's N-terminus on reconstituted HDLs (rHDLs) of different sizes. We have now investigated at the single-residue level the conformational adaptations of three regions in the central domain of apoA-I (residues 119-124, 139-144, and 164-170) upon apoA-I lipid binding and HDL formation. An important function associated with these residues of apoA-I is the activation of lecithin:cholesterol acyltransferase (LCAT), the enzyme responsible for catalyzing HDL maturation. Structural examination was performed by site-directed tryptophan fluorescence and spin-label electron paramagnetic resonance spectroscopies for both the lipid-free protein and rHDL particles 7.8, 8.4, and 9.6 nm in diameter. The two methods provide complementary information about residue side chain mobility and molecular accessibility, as well as the polarity of the local environment at the targeted positions. The modulation of these biophysical parameters yielded new insight into the importance of structural elements in the central domain of apoA-I. In particular, we determined that the loosely lipid-associated structure of residues 134-145 is conserved in all rHDL particles. Truncation of this region completely abolished LCAT activation but did not significantly affect rHDL size, reaffirming the important role of this structural element in HDL function