Molecular binding behavior of pyridine-2,6-dicarboxamide-bridged bis(beta-cyclodextrin) with oligopeptides: switchable molecular binding mode

Bridged bis(beta-cyclodextrin) 1 with a pyridine-2,6-dicarboxamide linker was synthesized, and its inclusion complexation behavior with some aliphatic oligopeptides was investigated in aqueous buffer solution of pH 2.0 and 7.2 at 25 degrees C by means of circular dichroism, fluorescence, and 2D NMR techniques. The results show that the resulting inclusion complexes of 1 with oligopeptides adopt a cooperative "cyclodextrin-guest-cyclodextrin" sandwich binding mode in a neutral media, but a "guest-linker-cyclodextrin" coinclusion binding mode in an acidic media. These switchable binding modes consequently rationalize the binding ability of bis(beta-cyclodextrin) 1 at different pH values; that is, 1 shows the stronger association with oligopeptides in a neutral media. Because of the simultaneous contributions of hydrophobic, hydrogen bond, and electrostatic interactions, bis(beta-cyclodextrin) 1 affords length-selectivity up to 4.7 for the Gly-Gly/Gly-Gly-Gly pair at pH 2.0 and sequence-selectivity up to 4.2 for the Gly-Leu/Leu-Gly pair at pH 7.2. These phenomena are discussed from the viewpoint of the size-fit concept and the multipoint recognitions between host and guest.     

The role of minor groove functional groups in DNA hydration

Here we describe the crystal structure of modified [d(CGCGAATTCGCG)]₂ refined to 2.04 Å. The modification, which affects only the two thymines at the central ApT step, involves isosteric removal of the 2-keto oxygen atoms and substitution of the N1 nitrogen with carbon. The crystal structure reveals the ability of this modified thymine to effectively base pair with adenine in [d(CGCGAAtTCGCG)]₂. The structure also suggests that the minor groove ‘spine of hydration’ is destabilized but essentially intact.     

Copper complex of hydroxyl-substituted triazamacrocyclic ligand and its antitumor activity

The protonation constants and the stability constants for the formation of copper (II) complex of the ligand [1,4,7] Triazecan-9-ol (L) were presented. Antitumor activity of CuL complex was reported. Preliminary pharmacological tests showed that it had antitumor activity against HXO-RB44 and BEL-7402 cell lines in vitro. Nuclei of [CuL]-stimulated BEL-7402 cells clearly exhibited condensation and break down into chromatin clumps typical of apoptosis. Also it exhibited perturbation effects to BEL-7402 cell lines cycle and further studies showed that it could cleave supercoiled DNA (pBR 322) to nicked and linear DNA.     

Fitness reduction and potential extinction of wild populations of Atlantic salmon, Salmo salar, as a result of interactions with escaped farm salmon

The high level of escapes from Atlantic salmon farms, up to two million fishes per year in the North Atlantic, has raised concern about the potential impact on wild populations. We report on a two-generation experiment examining the estimated lifetime successes, relative to wild natives, of farm, F(1) and F(2) hybrids and BC(1) backcrosses to wild and farm salmon. Offspring of farm and "hybrids" (i.e. all F(1), F(2) and BC(1) groups) showed reduced survival compared with wild salmon but grew faster as juveniles and displaced wild parr, which as a group were significantly smaller. Where suitable habitat for these emigrant parr is absent, this competition would result in reduced wild smolt production. In the experimental conditions, where emigrants survived downstream, the relative estimated lifetime success ranged from 2% (farm) to 89% (BC(1) wild) of that of wild salmon, indicating additive genetic variation for survival. Wild salmon primarily returned to fresh water after one sea winter (1SW) but farm and 'hybrids' produced proportionately more 2SW salmon. However, lower overall survival means that this would result in reduced recruitment despite increased 2SW fecundity. We thus demonstrate that interaction of farm with wild salmon results in lowered fitness, with repeated escapes causing cumulative fitness depression and potentially an extinction vortex in vulnerable populations.     

Solid-phase synthesis and biochemical evaluation of conformationally constrained analogues of deglycobleomycin A5

Deglycobleomycin binds to and degrades the self-complementary oligonucleotide d(CGCTAGCG)(2) in a sequence selective fashion. A previous modeling study [J. Am. Chem. Soc. 120, (1998), 7450] had shown that, during binding to double stranded DNA, the conformation of the methylvalerate domain of deglycoBLM approximated that of S-proline. In the belief that an analogue of deglycoBLM structurally constrained to mimic the DNA-bound conformation might exhibit facilitated DNA binding and cleavage, an analogue of deglycoBLM was prepared in which the methylvalerate moiety was replaced by S-proline. This deglycoBLM analogue, as well as the related analogue containing R-proline, was synthesized on a TentaGel resin. Both of the analogues were found to be capable of binding Fe(2+) and activating O(2) for transfer to styrene. However, both deglycoBLM analogues exhibited diminished abilities to effect the relaxation of supercoiled plasmid DNA, and neither mediated sequence selective DNA cleavage.     

Crystal structures of substrate complexes of malic enzyme and insights into the catalytic mechanism

Malic enzymes catalyze the oxidative decarboxylation of L-malate to pyruvate and CO(2) with the reduction of the NAD(P)(+) cofactor in the presence of divalent cations. We report the crystal structures at up to 2.1 A resolution of human mitochondrial NAD(P)(+)-dependent malic enzyme in different pentary complexes with the natural substrate malate or pyruvate, the dinucleotide cofactor NAD(+) or NADH, the divalent cation Mn(2+), and the allosteric activator fumarate. Malate is bound deep in the active site, providing two ligands for the cation, and its C4 carboxylate group is out of plane with the C1-C2-C3 atoms, facilitating decarboxylation. The divalent cation is positioned optimally to catalyze the entire reaction. Lys183 is the general base for the oxidation step, extracting the proton from the C2 hydroxyl of malate. Tyr112-Lys183 functions as the general acid-base pair to catalyze the tautomerization of the enolpyruvate product from decarboxylation to pyruvate.     

Two amino acids on 2a polymerase of<Emphasis Type="Italic">Cucumber mosaic virus</Emphasis> co-determine hypersensitive response on legumes

The hypersensitive response (HR) is one of the most important defense responses during the incompatible interaction between plant and pathogen. The viral determinant of HR on legumes induced byCucumber mosaic virus (CMV) was studied, and our previous results showed that 243 nucleotides on 2a polymerase gene of CMV were involved in the induction of HR on legumes. With further analysis of the nucleotides and amino acids in this region, the amino acids Phe and Ala at positions 631 and 641 in the 2a polymerase of CMV-Fny, a legume local necrotic strain, were specifically exchanged to Tyr and Ser, respectively and simultaneously, in the 2a polymerase of CMV-P1, a legume systemic infecting strain, and three point mutants were constructed. The point mutant Fny-F/Y (Phe631 to Tyr) induced large necrotic lesions instead of pinpoint lesions, and the size of lesions could enlarge from initial sites. The point mutant Fny-A/S (Ala641 to Ser) induced similar symptoms as CMV-Fny. The double-point mutant Fny-FA/YS (Phe631 to Tyr and Ala641 to Ser) infected the legumes systemically without HR. These data indicate that the induction of HR on legumes is co-determined by two amino acids at positions 631 and 641 in CMV 2a polymerase.     

Inhibition of established subcutaneous and metastatic murine tumors by intramuscular electroporation of the interleukin-12 gene

In vivo electroporation (EP) of the murine interleukin-12 (IL-12) gene in an expression plasmid (pIL-12) was evaluated for antitumor activity. EP transfer of pIL-12 into mouse quadriceps muscles elicited significant levels of serum IL-12 and interferon-gamma. Intramuscular EP of pIL-12 resulted in complete regression or substantial inhibition of 38C13 B-cell lymphoma, whereas pIL-12 delivered by gene gun or intramuscular injection without EP showed little therapeutic effect. Impressive antitumor activity by intramuscular EP was also demonstrated in animals with advanced malignant disease. At day 14 after 38C13 tumor inoculation, all animals were found to carry large tumors and to have metastases; without treatment, most died within a week. A single intramuscular EP of pIL-12 resulted in regression of 50% of large subcutaneous tumors and significantly prolonged the lifespan of these animals. Moreover, animals that were previously cured of 38C13 tumors by in vivo EP treatment significantly suppressed tumor growth when challenged 60 days later. In vivo EP of the IL-12 gene was also effective in suppressing subcutaneous and lung metastatic tumors of CT-26 colon adenocarcinoma and B16F1 melanoma cells. Together, these results show that intramuscular electrotransfer of the IL-12 gene may represent a simple and effective strategy for cancer treatment.     

Regulation of pollen tube growth by Rac-like GTPases

Plant Rac-like GTPases have been classified phylogenetically into two major groups-class I and class II. Several pollen-expressed class I Rac-like GTPases have been shown to be important regulators of polar pollen tube growth. The functional participation by some of the class I and all of the class II Arabidopsis Rac-like GTPases in pollen tube growth remains to be explored. It is shown that at least four members of the Arabidopsis Rac GTPase family are expressed in pollen, including a class II Rac, AtRac7. However, when over-expressed as fusion proteins with GFP, both pollen- and non-pollen-expressed AtRacs interfered with the normal pollen tube tip growth process. These observations suggest that these AtRacs share similar biochemical activities and may integrate into the pollen cellular machinery that regulates the polar tube growth process. Therefore, the functional contribution by individual Rac GTPase to the pollen tube growth process probably depends to a considerable extent on their expression characteristics in pollen. Among the Arabidopsis Racs, GFP-AtRac7 showed association with the cell membrane and Golgi bodies, a pattern distinct from all previously reported localization for other plant Racs. Over-expressing GFP-AtRac7 also induced the broadest spectrum of pollen tube growth defects, including pollen tubes that are bifurcated, with diverted growth trajectory or a ballooned tip. Transgenic plants with multiple copies of the chimeric Lat52-GFP-AtRac7 showed severely reduced seed set, probably many of these defective pollen tubes were arrested, or reduced in their growth rates that they did not arrive at the ovules while they were still receptive for fertilization. These observations substantiate the importance of Rac-like GTPases to sexual reproduction.