Chemistry & biology最新文献

The ZTP riboswitch is a widespread family of regulatory RNAs that upregulate de novo purine synthesis in response to increased intracellular levels of ZTP or ZMP. As an important intermediate in purine biosynthesis, ZMP also serves as a proxy for the concentration of N10-formyl-tetrahydrofolate, a key component of one-carbon metabolism. Here, we report the structure of the ZTP riboswitch bound to ZMP at a resolution of 1.80 Å. The RNA contains two subdomains brought together through a long-range pseudoknot further stabilized through helix-helix packing. ZMP is bound at the subdomain interface of the RNA through a set of interactions with the base, ribose sugar, and phosphate moieties of the ligand. Unique to nucleobase recognition by RNAs, the Z base is inner-sphere coordinated to a magnesium cation bound by two backbone phosphates. This interaction, along with steric hindrance by the backbone, imparts specificity over chemically similar compounds such as ATP/AMP.

Pictet-Spenglerases catalyze key condensation/cyclization reactions between aromatic ethylamines and aldehydes in the biosynthesis of alkaloids. In this issue of Chemistry & Biology, Mori et al. (2015) report the structural elucidation of a novel type of Pictet-Spenglerase involved in the biosynthesis of the β-carboline alkaloids.

Macrocyclases and other posttranslational enzymes afford derived peptides with improved properties for pharmaceutical and biotechnological applications. Here, we asked whether multiple posttranslational modifications could be simultaneously controlled and matched to rationally generate new peptide derivatives. We reconstituted the cyanobactin peptide natural products in vitro with up to five different posttranslational enzymes in a single tube. By manipulating the order of addition and identity of enzymes and exploiting their broad-substrate tolerance, we engineered the production of highly unnatural derivatives, including an N-C peptide macrocycle of 22 amino acids in length. In addition to engineering, this work better defines the macrocyclization mechanism, provides the first biochemical demonstration of Ser/Thr posttranslational prenylation, and is the first example of reconstitution of a native, multistep RiPP pathway with multiple enzymes in one pot. Overall, this work demonstrates how the modularity of posttranslational modification enzymes can be used to design and synthesize desirable peptide motifs.

Synthetic pyrrole (P)-imidazole (I) containing polyamides can target predetermined DNA sequences and modulate gene expression by interfering with transcription factor binding. We have previously shown that rationally designed polyamides targeting the inverted CCAAT box 2 (ICB2) of the topoisomerase IIα (topo IIα) promoter can inhibit binding of transcription factor NF-Y, re-inducing expression of the enzyme in confluent cells. Here, the A/T recognizing fluorophore, p-anisylbenzimidazolecarboxamido (Hx) was incorporated into the hybrid polyamide HxIP, which fluoresces upon binding to DNA, providing an intrinsic probe to monitor cellular uptake. HxIP targets the 5'-TACGAT-3' sequence of the 5' flank of ICB2 with high affinity and sequence specificity, eliciting an ICB2-selective inhibition/displacement of NF-Y. HxIP is readily taken up by NIH3T3 and A549 cells, and detected in the nucleus within minutes. Exposure to the polyamide at confluence resulted in a dose-dependent upregulation of topo IIα expression and enhanced formation of etoposide-induced DNA strand breaks.

Regulatory mechanisms underlying γH2AX induction and the associated cell fate decision during DNA damage response (DDR) remain obscure. Here, we discover a bromodomain (BRD)-like module in DNA-PKcs (DNA-PKcs-BRD) that specifically recognizes H2AX acetyl-lysine 5 (K5ac) for sequential induction of γH2AX and concurrent cell fate decision(s). First, top-down mass spectrometry of radiation-phenotypic, full-length H2AX revealed a radiation-inducible, K5ac-dependent induction of γH2AX. Combined approaches of sequence-structure modeling/docking, site-directed mutagenesis, and biochemical experiments illustrated that through docking on H2AX K5ac, this non-canonical BRD determines not only the H2AX-targeting activity of DNA-PKcs but also the over-activation of DNA-PKcs in radioresistant tumor cells, whereas a Kac antagonist, JQ1, was able to bind to DNA-PKcs-BRD, leading to re-sensitization of tumor cells to radiation. This study elucidates the mechanism underlying the H2AX-dependent regulation of DNA-PKcs in ionizing radiation-induced, differential DDR, and derives an unconventional, non-catalytic domain target in DNA-PKs for overcoming resistance during cancer radiotherapy.

DNMT1, the most abundant human methyltransferase, is responsible for translating the correct methylation pattern during DNA replication, and aberrant methylation by DNMT1 has been linked to tumorigenesis. We have developed a sensitive signal-on electrochemical assay for the measurement of DNMT1 activity in crude tissue lysates. We have further analyzed ten tumor sets and have found a direct correlation between DNMT1 hyperactivity and tumorous tissue. In the majority of samples analyzed, the tumorous tissue has significantly higher DNMT1 activity than the healthy adjacent tissue. No such correlation is observed in measurements of DNMT1 expression by qPCR, DNMT1 protein abundance by western blotting, or DNMT1 activity using a radiometric DNA labeling assay. DNMT1 hyperactivity can result from both protein overexpression and enzyme hyperactivity. DNMT1 activity measured electrochemically provides a direct measure of activity in cell lysates and, as a result, provides a sensitive and early indication of cancerous transformation.

Accumulating evidence has linked G-quadruplex structures to a number of biological processes in vivo, including DNA replication, transcription, and genomic maintenance. However, the precise function and mechanism of G-quadruplex formation in mammalian cells remains poorly defined. Therefore, the development of small-molecule G-quadruplex probes has attracted significant attention in recent years. This review highlights examples of G-quadruplex probes that have been reported over the last few years, some of which have been employed for cellular imaging or for use in the construction of G-quadruplex-based analytical sensing platforms.

In this issue of Chemistry & Biology, Cognetta et al. (2015) describe new pharmacological tools, including N-hydroxyhydantoin-containing carbamate inhibitors and an activity-based probe, for palmitoyl protein thioesterase 1 and alpha, beta-hydrolase domain-4 that expand the toolkit for the serine hydrolases.

Aberrant epigenetic methylation is linked to the onset and progression of cancer. In this issue of Chemistry & Biology, Furst and Barton (2015) describe a sensitive electrochemical assay that can detect hyperactive epigenetic methylation in tumor tissue.

Although transgene-based reporter gene assays have been used to discover small molecules targeting expression of cancer-driving genes, the success is limited due to the fact that reporter gene expression regulated by incomplete cis-acting elements and foreign epigenetic environments does not faithfully reproduce chemical responses of endogenous genes. Here, we present an internal ribosome entry site-based strategy for bicistronically co-expressing reporter genes with an endogenous gene in the native gene locus, yielding an in situ reporter assay closely mimicking endogenous gene expression without disintegrating its function. This strategy combines the CRISPR-Cas9-mediated genome-editing tool with the recombinase-mediated cassette-exchange technology, and allows for rapid development of orthogonal assays for excluding false hits generated from primary screens. We validated this strategy by developing a screening platform for identifying compounds targeting oncogenic eIF4E, and demonstrated that the novel reporter assays are powerful in searching for transcription-targeted lead compounds with high confidence.