Deazapurine-containing secondary metabolites comprise a broad range of structurally diverse nucleoside analogs found throughout biology including various antibiotics produced by species of Streptomyces bacteria and the hypermodified tRNA bases queuosine and archaeosine. Despite early interest in deazapurines as antibiotic, antiviral, and antineoplastic agents, the biosynthetic route toward deazapurine production has remained largely elusive for more than 40 years. Here we present the first in vitro preparation of the deazapurine nucleoside, preQ 0 , by the successive action of four enzymes. The pathway includes the conversion of the recently identified biosynthetic intermediate, 6-carboxy-5,6,7,8-tetrahydropterin, to a novel intermediate, 7-carboxy-7-deazaguanine (CDG), by an unusual transformation catalyzed by B. subtilis QueE, a member of the radical SAM enzyme superfamily. The carboxylate moiety on CDG is converted subsequently to a nitrile to yield preQ 0 by either B. subtilis QueC or S. rimosus ToyM in an ATP-dependent reaction, in which ammonia serves as the nitrogen source. The results presented here are consistent with early radiotracer studies on deazapurine biosynthesis and provide a unified pathway for the production of deazapurines in nature.Compounds containing pyrrolopyrimidine functional groups, collectively referred to as 7-deazapurines, are a structurally diverse class of nucleoside analogs with demonstrated antibiotic, antineoplastic, and antiviral activities. Deazapurine containing compounds include the nucleoside antibiotics toyocamycin, sangivamycin, tubercidin, and cadeguomycin ( Figure 1), which are produced by various species of Streptomyces (1,2). In addition, the hypermodified base, queuosine (Figure 1), which is located in the wobble position of 5′-GUN-3′ anticodons in tRNA in a number of organisms (except yeast (3)) bearing tyrosine, histidine, asparagine and aspartate contains a deazapurine moiety (4). The occurrence of queuosine in tRNA is

Differentiation of the physiological role of the melanocortin receptor 5 MC5R from that of other melanocortin receptors will require development of high affinity and selective antagonists. To date, a few synthetic antagonist ligands active at hMC5 receptor are available, but most do not have appreciable selectivity. With the aim to gain more potent and selective antagonists for the MC5R ligands, we have designed, synthesized, and pharmacologically characterized a series of alkylthioaryl-bridged macrocyclic peptide analogues derived from MT-II and SHU9119. These 20-membered macrocycles were synthesized by a tandem combination using solid phase peptide synthesis and microwave-assisted reactions. Biological assays for binding affinities and adenylate cyclase activities for the hMC1R, hMC3R, hMC4R, and hMC5R showed that three analogues, compounds, 9, 4, and 7, are selective antagonists at the hMC5 receptor. In particular, compound 9 (PG-20N) is a selective and competitive hMC5R antagonist, with IC 50 of 130 ± 11 nM, and a pA 2 value of 8.3, and represents an important tool for further biological investigations of the hMC5R. Compounds 4 and 7 (PG14N, PG17N) show potent and selective allosteric inhibition at hMC5R with IC 50 values of 38 ± 3 nM and 58 ± 6 nM, respectively. Compound 9 will be used to further investigate and more clearly understand the physiological roles played by the MC5 receptor in humans and other animals.

Werner syndrome (WS) is an autosomal recessive disease that results in premature aging. Mutations in the WS gene (WRN) result in a loss of expression of the WRN protein and predispose WS patients to accelerated aging. As a helicase and a nuclease, WRN is unique among the five human RecQ helicase family members and is capable of multiple functions involved in DNA replication, repair, recombination, and telomere maintenance. A 144-residue fragment of WRN was previously determined to be a multifunctional DNA-and protein-binding domain (DPBD) that interacts with structure-specific DNA and a variety of DNA-processing proteins. In addition, DPBD functions as a nucleolar targeting sequence of WRN. The solution structure of the DPBD, the first of a WRN fragment, has been solved by NMR. DPBD consists of a winged helix-like motif and an unstructured C-terminal region of Ϸ20 aa. The putative DNA-binding surface of DPBD has been identified by using known structural and biochemical data. Based on the structural data and on the biochemical data, we suggest a surface on the DPBD for interacting with other proteins. In this structural model, a single winged helix domain binds to both DNA and other proteins. Furthermore, we propose that DPBD functions as a regulatory domain to regulate the enzymatic activity of WRN and to direct cellular localization of WRN through protein-protein interaction.DNA-and protein-binding domain ͉ functional regulation ͉ NMR structure ͉ winged helix

Hydrogen cyanide is considered as an important precursor to amino acids and nucleic acids, and its polymers could have profound implications on prebiotic chemistry. Several structures of HCN polymers are speculated, but these structures are disparate both chemically as well as structurally. Here, we employ solution-state NMR spectroscopy to investigate the structure of HCN polymers with (13)C and (15)N isotopic enrichment. From the multinuclear and multidimensional NMR investigations, we identify some discrete structural units for the most concentrated small molecular components and suggest that the dominating polymers are polyimine chain-like structures, which are formed by base-catalyzed nucleophilic addition reactions.