Abstract only
Cytosine methylation at CpG dinucleotides is central to transcriptional regulation and genome stability and is implicated in genetic disease, cancer, and ageing, a prominent mechanism ...involving 5‐methylcytosine deamination to give mutagenic G•T mispairs. Human thymine DNA glycosylase (hTDG) excises T from G•T mismatches, and removes other damaged bases, and has specificity for lesions paired with guanine and located at CpG sites. The molecular basis of these important catalytic properties has remained unknown. Here, we report a crystal structure of hTDG (catalytic domain) in complex with abasic DNA reveals that it binds as a protein dimer, one subunit at the abasic site and the other at an undamaged (nonspecific) site. The structure also reveals interactions that provide selectivity for guanine versus adenine as the pairing partner of the target base, and interactions that confer sequence specificity, a highly unusual capability for a DNA glycosylase. We find striking and unexpected differences between hTDG and its prokaryotic ortholog, mismatch‐specific uracil DNA glycosylase (MUG), despite high (32%) sequence identity. This work was supported by a grant from the National Institutes of Health and University of Maryland Greenebaum Cancer Center.
Thyroid malfunction is more common in individuals with Down syndrome (DS) than in the general population. It has been hypothesized that thyroid may influence cancer risk. Individuals with DS are at ...greater risk of developing leukemia than the general population, while solid tumors especially breast cancer (BC) are rare. BC patients have higher levels of circulating thyroid-stimulating hormone (TSH) and prolactin (PRL), both regulated by the thyrotropin-releasing hormone (TRH), a hypothalamic tripeptide. This study was aimed at investigating the status of TRH functional polymorphisms in subjects with DS and BC. Unrelated families with DS probands (n=180), individuals with BC (n=99) and ethnically matched controls (n=216) were recruited. Genomic DNA isolated from peripheral blood was subjected to PCR amplification followed by DNA sequence analysis. Data obtained were analyzed by population- and family-based statistical analysis. Among 30 studied sites, only 2 (rs7645772 and rs13097335) were polymorphic. Case-control analysis showed a lack of any significant association with DS, while the rs13097335 GG and GT genotype frequency was significantly different in the BC samples. A paternal-biased transmission of the G allele was observed in female DS probands. It may be concluded that rs13097335 may have a protective role toward the development of BC.
Brain derived neurotrophic factor (BDNF) regulates growth and regeneration. It can also modulate the activity of voltage gated ion channels. It has been reported that activation of BDNF receptor TrkB ...(neurotropin receptor tyrosine kinase B) suppresses voltage gated potassium channel (Kv 1.5) via phosphorylation of multiple tyrosine residues (BS Colley et. al 2007 Neuroscience 144:531–46). It is not known how ion channel proteins, which lack catalytic activity, interact with BDNF signaling pathway. In this study we cloned Kv 1.5 gene into GFP expressing vector and transfected the gene into HeLa cell with jetPRIME reagent (80 % transfection efficiency). Western blot analysis revealed that the protein expression of Kv 1.5 was significantly increased in Kv 1.5 over expressing cells as compared to cells which were not transfected. However, with BDNF or 7,8 dihydroxyflavone, a TrkB agonist, the expression of Kv 1.5 protein was significantly reduced. We further demonstrated that in Kv 1.5 over expressing cells treated with either BDNF or 7,8 dihydroxyflavone, the Akt and STAT‐3 signaling pathways were stimulated. Collectively our findings suggest that increased BDNF activity in Kv1.5 over expressing cells contributes to the reduction in Kv 1.5 protein expression and probably the channel functions through TrkB receptor stimulation which triggers Akt and STAT‐3 cell survival pathways. This work is funded by a VA grant.
The specificity of protein–nucleic acid recognition is believed to originate largely from hydrogen bonding between protein polar atoms, primarily side-chain and polar atoms of nucleic acid bases. One ...way to design new nucleic acid binding proteins of novel specificity is by structure-guided alterations of the hydrogen bonding patterns of a nucleic acid–protein complex. We have used cI repressor of bacteriophage λ as a model system. In the λ-repressor–DNA complex, the ε-NH2 group (hydrogen bond donor) of lysine-4 of λ-repressor forms hydrogen bonds with the amide carbonyl atom of asparagine-55 (acceptor) and the O6 (acceptor) of CG6 of operator site OL1. Substitution of lysine-4 (two donors) by iso-steric S-(2-hydroxyethyl)-cysteine (one donor and one acceptor), by site-directed mutagenesis and chemical modification, leads to switch of binding specificity of λ-repressor from C:G to T:A at position 6 of OL1. This suggests that unnatural amino acid substitutions could be a simple way of generating nucleic acid binding proteins of altered specificity.
Defunctionalization has a direct impact on the synthesis of value added products (
e.g.
biomass degradation). In synthetic chemistry it enables the functional group to act as a transient directing ...group. In this mini review, we have described the chronological development of metal assisted defunctionalization reactions from the stoichiometric to the catalytic stage with their application in synthetic organic chemistry. The proposed catalytic cycles of the transformations have been described to make this review comprehensible.
The chronological development of metal assisted defunctionalization reactions is discussed from the stoichiometric to the catalytic stage with their application in synthetic organic chemistry.
A nitrile-based template attached with a phenylacetic acid framework promoted meta-selective C–H bond olefination. This palladium-catalyzed protocol is applicable to a wide range of substituted ...phenylacetic acids and tolerates a variety of functional groups. The versatility of this operationally simple method has been demonstrated through drug diversification.
Various practical methods for the selective C−H functionalization of the ortho and recently also of the meta position of an arene have already been developed. Following our recent development of the ...directing‐group‐assisted para C−H functionalization of toluene derivatives, we herein report the first remote para C−H functionalization of phenol derivatives by using a recyclable silicon‐containing biphenyl‐based template. The effectiveness of this strategy was illustrated with different synthetic elaborations and by the synthesis of various phenol‐based natural products.
The template‐assisted para C−H olefination of phenol derivatives was enabled by a silicon‐containing directing group (DG; see scheme) in combination with a palladium catalyst. This method was also applied to the synthesis of different natural products.
Cost-effective and highly sensitive biocompatible probes for the detection of Al3+ have tremendously important practical applications. Herein, we report for the first time, the hydrazinopyrimidine ...based Al3+ chemosensor L (1-(4,6-dimethyl-pyrimidin-2-yl)-hydrazonomethyl-naphthalen-2-ol) prepared by the condensation of 2-hydroxy-1-naphthaldehyde and 4,6-dimethyl-2-hydrazino-pyrimidine. Our as-synthesized chemosensor L (Φ = 0.0066) shows ∼15 fold fluorescence enhancement in the presence of Al3+ (Φ = 0.0955, Ka = 1.9 × 104 M−1) via chelation enhanced fluorescence (CHEF), excited state intramolecular proton transfer (ESIPT), and inhibited photo-induced electron transfer (PET) phenomena. The limit of detection (LOD) and limit of quantification (LOQ) were estimated to be 2.78 μM and 9.27 μM, respectively. Furthermore, for the first time, a hydrazino pyrimidine based ‘INHIBIT’ molecular logic gate for Al3+ was successfully developed using the fluorescence properties of L. The experimental sensing mechanisms of L for Al3+ were corroborated by theoretical calculations. Biocompatibility and good water-solubility properties of a pyrimidine moiety of L inspired us to investigate Al3+ imaging in human embryonic kidney cell lines, HEK293, and the results for practical applications are highly promising.
Site-selective C–H functionalization has emerged as an efficient tool in simplifying the synthesis of complex molecules. Most often, directing group (DG)-assisted metallacycle formation serves as an ...efficient strategy to ensure promising regioselectivity. A wide variety of ortho- and meta-C–H functionalizations stand as examples in this regard. Yet despite this significant progress, DG-assisted selective para-C–H functionalization in arenes has remained unexplored, mainly because it involves the formation of a geometrically constrained metallacyclic transition state. Here we report an easily recyclable, novel Si-containing biphenyl-based template that directs efficient functionalization of the distal p-C–H bond of toluene by forming a D-shaped assembly. This DG allows the required flexibility to support the formation of an oversized pre-transition state. By overcoming electronic and steric bias, para-olefination and acetoxylation were successfully performed while undermining o- and m-C–H activation. The applicability of this D-shaped biphenyl template-based strategy is demonstrated by synthesizing various complex molecules.
PDF
