No abstract

Enantiomerically pure a-amino-acid derivatives with the side chains of A h , Val, and Leu in the 2-or 3-position (8'-and P3-amino acids, resp.), as well as with substituents in both the 2-and 3-positions (Pz.3-amino acids, of like-configuration) have been prepared (compounds 8-17) and incorporated (by stepwise synthesis and fragment coupling, intermediates 24-34) into P-hexa-, P-hepta-, and j-dodecapeptides (1 -17). The new and some of the previously prepared P-peptides (35-39) showed NHiND exchange rates (in MeOH at room temperature) with T~,~ values of up to 60 days, unrivalled by short chain a-peptides. All P-peptides 1-7 were designed to be able to attain the previously described 3,-helical structure (Figs. I and 2). C D Measurements (Fig. 4), indicating a new secondary structure of certain P-peptides constructed of P'-and p3-arnino acids, were confirmed by detailed NMR solution-structure analyses: a P*-heptapeptide (2c) and a Pz.3-hexapeptide (7c) have the 3,-helical structure (Figs. 6 and 7), while to a P2/P3-hexapeptide (4) with alternating substitution pattern H-(P2-Xaa-P3-Xaa),-OH a novel, unusual helical structure (in (DJpyridine, Fig. 8; and in CD30H, Figs. 9 and f0) was assigned, with a central ten-membered and two terminal twelve-membered H-bonded rings, and with C=O and N-H bonds pointing alternatively up and down along the axis of the helix (Fig. 11). Thus, for the first time, two types of fi-peptide turns have been identified in solution. Hydrophobic interactions ofand hindrance to solvent accessibility by the aliphatic side chains are discussed as possible factors influencing the relative stability of the two types of helices.

The relationship between corals and dinoflagellates of the genus is fundamental to the functioning of coral ecosystems. It has been suggested that reef corals may adapt to climate change by changing their dominant symbiont type to a more thermally tolerant one, although the capacity for such a shift is potentially hindered by the compatibility of different host-symbiont pairings. Here we combined transcriptomic and metabolomic analyses to characterize the molecular, cellular, and physiological processes that underlie this compatibility, with a particular focus on, an opportunistic, thermally tolerant symbiont that flourishes in coral tissues after bleaching events. Symbiont-free individuals of the sea anemone (commonly referred to as Aiptasia), an established model system for the study of the cnidarian-dinoflagellate symbiosis, were colonized with the "normal" (homologous) symbiont and the heterologous Analysis of the host gene and metabolite expression profiles revealed that heterologous symbionts induced an expression pattern intermediate between the typical symbiotic state and the aposymbiotic state. Furthermore, integrated pathway analysis revealed that increased catabolism of fixed carbon stores, metabolic signaling, and immune processes occurred in response to the heterologous symbiont type. Our data suggest that both nutritional provisioning and the immune response induced by the foreign "invader" are important factors in determining the capacity of corals to adapt to climate change through the establishment of novel symbioses.

Dedicated to Professor Hans Paulsen on the occasion of his 75th birthday (23.XII. 1996) The solid-state structures of three stereoisomers, 1-3, of the cyclic tetramer of 3-aminobutanoic acid are presented. These cyclo-p-peptides were found to be highly insoluble materials, and it proved to be impossible to grow crystals of suficient quality for X-ray single-crystal analysis. The samples of 1-3 were, however, suitable candidates for structure determination from powder diffraction data (Fig. Z), and the application of this method is described. All three isomers have been found to adopt tubular structures (Figs. 2-4) in a fashion similar to those already observed for certain cyclo-a-peptides. The stacks of 16-membered rings are held together by four nonlinear C=O ...H-N H-bonds between pairs of molecules (Fig. 5 ) .

fi-Hexapeptides 1-5 and a 8-dodecapeptide 6 with sequences containing two different types of fi-amino acids (aliphatic proteinageous side chains in the 2-or in the 3-position) have been prepared. CD (Fig. f) and NMR measurements indicate that, with one exception, the secondary structures formed by these new 8-peptides differ from those of isomers studied previously. Detailed NMR analysis of the 8-hexapeptide 5 (with alternating fiZ,fi3-building blocks) and molecular-dynamics simulations have produced a minimum energy conformation (Fig. 2,b) which might be described as a novel irregular helix containing ten-and twelve-membered H-bonded rings. This demonstrates the great structural variability of fi-peptides, since three different helical secondary structures have been discovered to date. ' ) 3,Part of the projected Ph. D. theses of K.G. and ZH., ETH-Zurich.

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Metabolite exchange is fundamental to the viability of the cnidarian-Symbiodiniaceae symbiosis and survival of coral reefs. Coral holobiont tolerance to environmental change might be achieved through changes in Symbiodiniaceae species composition, but differences in the metabolites supplied by different Symbiodiniaceae species could influence holobiont fitness. Using 13 C stable-isotope labelling coupled to gas chromatography-mass spectrometry, we characterized newly fixed carbon fate in the model cnidarian Exaiptasia pallida (Aiptasia) when experimentally colonized with either native Breviolum minutum or non-native Durusdinium trenchii. Relative to anemones containing B. minutum, D. trenchii-colonized hosts exhibited a 4.5-fold reduction in 13 C-labelled glucose and reduced abundance and diversity of 13 C-labelled carbohydrates and lipogenesis precursors, indicating symbiont species-specific modifications to carbohydrate availability and lipid storage. Mapping carbon fate also revealed significant alterations to host molecular signalling pathways. In particular, D. trenchii-colonized hosts exhibited a 40-fold reduction in 13 C-labelled scyllo-inositol, a potential interpartner signalling molecule in symbiosis specificity. 13 C-labelling also highlighted differential antioxidant-and ammoniumproducing pathway activities, suggesting physiological responses to different symbiont species. Such differences in symbiont metabolite contribution and host utilization may limit the proliferation of stress-driven symbioses; this contributes valuable information towards future scenarios that select in favour of less-competent symbionts in response to environmental change.

During routine screening of zebrafish at a research facility, histological changes consistent with mycobacteriosis were observed, prompting an investigation to determine the background prevalence and distribution of Mycobacterium species throughout the facility. Infection status was evaluated in 240 zebrafish representing 9 genetic lines, using histology, culture and PCR. Environmental sources were also tested for the presence of mycobacteria. Prevalence in zebrafish by culture and PCR was 10% (24/240), 21 of which were TU line fish. All isolates from fish were identified as M. chelonae by hsp65 DNA sequencing; subsequent DNA fingerprinting delineated 3 strains, designated H1E1 (1/24), H1E2 (22/24), and H1E3 (1/24). From external sources, tank or tubing surface biofilms were positive by culture (13/32) with multiple species and strains isolated including M. neoaurum, M. phocaicum, and identical strains of M. chelonae that were found in zebrafish: H1E1 (2/13) and H1E2 (8/13). Comparing diagnostic methods, acid-fast stained histological sections showed substantial agreement with plate culture and PCR for detection of mycobacteria in fish. Observation of granulomas in hematoxylin and eosin-stained sections was a less reliable predictor of mycobacteriosis, as uninfected females with egg-associated inflammation and hyperplasia were misdiagnosed. These data revealed background levels of mycobacteriosis in a healthy and wellmanaged facility. Infected populations were removed, although the apparent ability for M. chelonae to remain viable in environmental reservoirs may make it difficult to eradicate completely. This highlights the importance of an animal-health monitoring program and good husbandry practices to prevent disease in zebrafish research laboratories. KEY WORDS: Mycobacterium chelonae · Zebrafish · Danio rerio · Biofilms · Enterobacterial repetitive intergenic consensus PCR · ERIC-PCR · Randomly amplified polymorphic DNA · RAPD Resale or republication not permitted without written consent of the publisherDis Aquat Org 82: [45][46][47][48][49][50][51][52][53][54] 2008 infect with low virulence and the opportunistic manifestation of disease may be a result of suboptimal environmental conditions.Even in the absence of mortalities, chronic underlying infections are a threat to the efficacy of results derived from experiments that employ zebrafish. As with any research animal (Baker 2003), it is imperative that disease be minimized. Acute diseases causing severe morbidity and mortality in zebrafish have been reported (Kent et al. 2004, Whipps et al. 2007a), but little is known about the distribution and prevalence of sub-clinical infections. Good husbandry practices likely minimize the potential spread of pathogens in a system, and when standard practices include a health monitoring program, infected stocks can be identified early and isolated or removed. Case in point, in January 2006, during routine monitoring at a zebrafish research laboratory, a few fish exhibiting lesions consistent with mycobac...