Enantioselective total synthesis of altersolanol A and N

The development of the first enantioselective total synthesis of altersolanol N is reported. The decisive step of the synthesis is the enantioselective formation of the tetrahydroanthraquinone nucleus by a [4 + 2]-cycloaddition in high yield and with excellent diastereo- and enantioselectivity (>95:5 dr and 95:5 er). In addition, a demanding selective monoacetylation of the OH group at the C-2 position was achieved: an epoxide ring opening with the participation of a neighbouring acetyl group could be established. The route proved to be an efficient alternative to also access enantiomerically pure altersolanol A.     

Flow-cytometric assessment of cellular poly(ADP-ribosyl)ation capacity in peripheral blood lymphocytes

Background  

Poly(ADP-ribosyl)ation is a posttranslational modification of nuclear proteins catalysed by poly(ADP-ribose) polymerases (PARPs), using NAD⁺ as a substrate. Activation of PARP-1 is in immediate response to DNA damage generated by endogenous and exogenous damaging agents. It has been implicated in several crucial cellular processes including DNA repair and maintenance of genomic stability, which are both intimately linked with the ageing process. The measurement of cellular poly(ADP-ribosyl)ation capacity, defined as the amount of poly(ADP-ribose) produced under maximal stimulation, is therefore relevant for research on ageing, as well as for a variety of other scientific questions.     

Co-expression and promoter content analyses assign a role in biotic and abiotic stress responses to plant natriuretic peptides

Background  

Plant natriuretic peptides (PNPs) are a class of systemically mobile molecules distantly related to expansins. While several physiological responses to PNPs have been reported, their biological role has remained elusive. Here we use a combination of expression correlation analysis, meta-analysis of gene expression profiles in response to specific stimuli and in selected mutants, and promoter content analysis to infer the biological role of the Arabidopsis thaliana PNP, AtPNP-A.     

Impact of aeration and heme-activated respiration on Lactococcus lactis gene expression: identification of a heme-responsive operon

Lactococcus lactis is a widely used food bacterium mainly characterized for its fermentation metabolism. However, this species undergoes a metabolic shift to respiration when heme is added to an aerobic medium. Respiration results in markedly improved biomass and survival compared to fermentation. Whole-genome microarrays were used to assess changes in L. lactis expression under aerobic and respiratory conditions compared to static growth, i.e., nonaerated. We observed the following. (i) Stress response genes were affected mainly by aerobic fermentation. This result underscores the differences between aerobic fermentation and respiration environments and confirms that respiration growth alleviates oxidative stress. (ii) Functions essential for respiratory metabolism, e.g., genes encoding cytochrome bd oxidase, menaquinone biosynthesis, and heme uptake, are similarly expressed under the three conditions. This indicates that cells are prepared for respiration once O(2) and heme become available. (iii) Expression of only 11 genes distinguishes respiration from both aerobic and static fermentation cultures. Among them, the genes comprising the putative ygfCBA operon are strongly induced by heme regardless of respiration, thus identifying the first heme-responsive operon in lactococci. We give experimental evidence that the ygfCBA genes are involved in heme homeostasis.     

The Lantibiotic NAI-107 Binds to Bactoprenol-bound Cell Wall Precursors and Impairs Membrane Functions

The lantibiotic NAI-107 is active against Gram-positive bacteria including vancomycin-resistant enterococci and methicillin-resistant Staphylococcus aureus. To identify the molecular basis of its potency, we studied the mode of action in a series of whole cell and in vitro assays and analyzed structural features by nuclear magnetic resonance (NMR). The lantibiotic efficiently interfered with late stages of cell wall biosynthesis and induced accumulation of the soluble peptidoglycan precursor UDP-N-acetylmuramic acid-pentapeptide (UDP-MurNAc-pentapeptide) in the cytoplasm. Using membrane preparations and a complete cascade of purified, recombinant late stage peptidoglycan biosynthetic enzymes (MraY, MurG, FemX, PBP2) and their respective purified substrates, we showed that NAI-107 forms complexes with bactoprenol-pyrophosphate-coupled precursors of the bacterial cell wall. Titration experiments indicate that first a 1:1 stoichiometric complex occurs, which then transforms into a 2:1 (peptide: lipid II) complex, when excess peptide is added. Furthermore, lipid II and related molecules obviously could not serve as anchor molecules for the formation of defined and stable nisin-like pores, however, slow membrane depolarization was observed after NAI-107 treatment, which could contribute to killing of the bacterial cell.