Chemical mutagens with an aromatic ring system may be enzymatically transformed to afford aryl radical species that preferentially react at the C8-site of 2′-deoxyguanosine (dG). The resulting carbon-linked C8-aryl-dG adduct possesses altered biophysical and genetic coding properties compared to the precursor nucleoside. Described herein are structural and in vitro mutagenicity studies of a series of fluorescent C8-aryl-dG analogues that differ in aryl ring size and are representative of authentic DNA adducts. These structural mimics have been inserted into a hotspot sequence for frameshift mutations, namely, the reiterated G3-position of the NarI sequence within 12mer (NarI(12)) and 22mer (NarI(22)) oligonucleotides. In the NarI(12) duplexes, the C8-aryl-dG adducts display a preference for adopting an anti-conformation opposite C, despite the strong syn preference of the free nucleoside. Using the NarI(22) sequence as a template for DNA synthesis in vitro, mutagenicity of the C8-aryl-dG adducts was assayed with representative high-fidelity replicative versus lesion bypass Y-family DNA polymerases, namely, Escherichia coli pol I Klenow fragment exo− (Kf−) and Sulfolobus solfataricus P2 DNA polymerase IV (Dpo4). Our experiments provide a basis for a model involving a two-base slippage and subsequent realignment process to relate the miscoding properties of C-linked C8-aryl-dG adducts with their chemical structures.
Bis(1,1,1-trifluoro-5,5-dimethyl-5-methoxy-acetylacetonato)copper(II) was prepared in two polymorphic modifications. The orthorhombic R-form is stable and densely packed, with four trans and four cis square bischelate building blocks per unit cell. These are connected through additional coordination bonds to form a dense polymer network. For the trigonal β-form, the square bischelate complex units are present exclusively as the trans isomers. The distinctive assembly of these units results in a lattice with an open pore volume of about 17% that is accessible to a wide range of guests. The compound has a remarkably strong affinity for the porous β-form as evident from the efficient R-to-β conversion on contact not only with liquid guests but also with organic vapors at pressures well below the saturation pressure. Although the open β-form is metastable, it has a remarkable kinetic stability, most likely because of the trans-to-cis isomerization that must accompany the β-to-R transformation. Many sorbents play a dual role as stabilizing guest and as catalyst promoting the R-to-β or β-to-R conversion. Because of its versatile sorption properties and relative robustness, the β-form of the complex can be classified as a novel organic zeolite mimic.
Robust porous frameworks are formed by the dipeptides L‐Ala‐L‐Val (see structure) and L‐Val‐L‐Ala that have a high capacity and selectivity for gas sorption. The dipeptides assemble through hydrogen bonds as a 61 helix to form channels with average diameters of 5.13 and 4.90 Å, respectively.
Background:The human innate immune system can discriminate between Candida albicans yeast and hyphal forms. Results: C. albicans hyphae possess glucan structures that are unique to the hyphae and are not found in yeast.
Conclusion: Hyphal glucan elicits robust immune responses.Significance: These data provide a structural basis for differential immune recognition of C. albicans yeast versus hyphae.
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