Mycosporines and mycosporine-like amino acids: UV protectants or multipurpose secondary metabolites?

Mycosporines and mycosporine-like amino acids (MAAs) are low-molecular-weight water-soluble molecules absorbing UV radiation in the wavelength range 310-365 nm. They are accumulated by a wide range of microorganisms, prokaryotic (cyanobacteria) as well as eukaryotic (microalgae, yeasts, and fungi), and a variety of marine macroalgae, corals, and other marine life forms. The role that MAAs play as sunscreen compounds to protect against damage by harmful levels of UV radiation is well established. However, evidence is accumulating that MAAs may have additional functions: they may serve as antioxidant molecules scavenging toxic oxygen radicals, they can be accumulated as compatible solutes following salt stress, their formation is induced by desiccation or by thermal stress in certain organisms, they have been suggested to function as an accessory light-harvesting pigment in photosynthesis or as an intracellular nitrogen reservoir, and they are involved in fungal reproduction. Here, the evidence for these additional roles of MAAs as 'multipurpose' secondary metabolites is reviewed, with special emphasis on their functions in the microbial world.     

Photosynthetic characteristics and mycosporine-like amino acids under UV radiation: a competitive advantage of Mastocarpus stellatus over Chondrus crispus at the Helgoland shoreline?

Chondrus crispus and Mastocarpus stellatus both inhabit the intertidal and upper sublittoral zone of Helgoland, but with C. crispus generally taking a lower position. Measurements of chlorophyll fluorescence, activity of ribulose-1,5-bisphosphate carboxylase/oxygenase (RubisCO), and content and composition of UV absorbing mycosporine-like amino acids (MAAs) were conducted in the laboratory, to test whether susceptibility to UV radiation may play a role in the vertical distribution of these two species. Effective and maximal quantum yield of photochemistry as well as maximal electron transport rate (ETR_max) in C. crispus were more strongly affected by UV-B radiation than in M. stellatus. In both species, no negative effects of the respective radiation conditions were found on total activity of RubisCO. Total MAA content in M. stellatus was up to 6-fold higher than in C. crispus and the composition of MAAs in the two species was different. The results indicate that, among others, UV-B sensitivity may be a factor restricting C. crispus to the lower intertidal and upper sublittoral zone, whereas M. stellatus is better adapted to UV radiation and is therefore more competitive in the upper intertidal zone. Received: 15 November 1999 / Received in revised form: 28 February 2000 / Accepted: 10 March 2000     

Stimulated uptake of amino acids by HeLa cells following ‘preloading’ in high concentrations of amino acids

HeLa cells exposed to 10mM leucine in medium for 30 mins at 37 °C showed greatly increased uptake of tritiated leucine when returned to medium containing 0.1mM levels of labelled amino acid. Further analysis of the phenomenon demonstrates that the steepness of the gradient is essential for rapid uptake to be observed, that no stereo-specificity is involved, and that the peak of uptake is followed by discharge with first order kinetics back to equilibrium. The effect of 14 different amino acids examined individually as 10mM supplements to the labelling medium ranged from slight reduction (lysine, proline) to complete suppression of the ‘stimulated uptake’ (phenylalanine, isoleucine).     

Molecular orbital calculation for the model compounds of kainoid amino acids, agonists of excitatory amino acid receptors. Does the kainoid C4-substituent directly interact with the receptors?

Kainoid amino acids are agonists of the AMPA/kainate receptors and exhibit highly potent neuroexcitatory activity. From the results of extensive structure--activity relationship studies, we previously postulated that the C4-substituent of the kainoid amino acids interacts with an allosteric site of the glutamate receptor with electron-donating character. In order to investigate the mode of action in more detail, molecular orbital calculation for model compounds of the kainoid were performed. The results indicated that the HOMO energy level of the C4-substituent is involved in the potent neuroexcitatory activity, thus supporting our hypothesis.     

Pulse radiolysis of aromatic amino acids — State of the art

Summary The pulse radiolysis method as well as the primary processes of water radiolysis and the spectroscopic characteristics of H, OH, HO₂/O₂ ^– and e _aq ^- are briefly presented. Subsequently, kinetic and spectroscopic data of the transients resulting from the resolved multi site attack on aromatic amino acids are discussed. The reactivity of H and e _aq ^- with the same substrates, as well as the effect of oxygen on the major radiolytic processes are reviewed. Finally, the formation of tryptophan radical cation is mentioned shortly. The presented radiation mechanisms are the fundamentals for radiolytic processes occurring in proteins, enzymes and hormones in the living cells.     

Two γ-Glutamylpeptides of acetylenic amino acids in Tricholomopsis rutilans

Two γ-glutamylpeptides, γ-L-glutamyl-L-2-aminohex-4-ynoic acid and γ-L-glutamyl-L-erythro-2-amino-3-hydroxyhex-4-ynoic acid,     

Occurrence of trans fatty acids in rats fed a trans-free diet: A free radical-mediated formation?

Trans isomers of unsaturated fatty acids are absorbed from the diet, due to their presence in diary fat and hydrogenated vegetable oils, and health concern has risen due to their effects on lipid risk factors in cardiovascular diseases. On the basis of the efficiency of the thiyl-radical-catalyzed cis/trans isomerization in vitro and the presence of many sulfur-containing compounds in the cell, the aim of this study was to demonstrate that trans geometry of lipid double bonds can be endogenously generated within membrane phospholipids. The study reports trans fatty acids occurrence in tissue and erythrocyte phospholipids of young adult rats fed a diet completely free of trans isomers. Results show that tissues are differently prone to the endogenous isomerization and that, following a free radical attack, trans fatty acids can reach very high amounts. The effectiveness of this process is considerably inhibited in the presence of all-trans retinol, confirming previous data in model membranes. Our results suggest that geometrical isomerization of unsaturated fatty acids, which causes a structural modification of membrane lipids and may influence basic membrane properties and vital biochemical functions, can occur under radical stress conditions and could be efficiently prevented by vitamin A.     

CuI-promoted one-pot synthesis of N-Boc protected β-ketotriazole amino acids: application in the synthesis of new class of dipeptidomimetics

One-pot click chemistry of N(α)-Boc-bromomethylketones, NaN3 and propiolic acid affords N-Boc protected 1,4-disubstituted 1,2,3-β-ketotriazole acids in good to excellent yield. The use of CuI as catalyst and DMSO as solvent leads the click reaction to efficient, practical and column-free preparation of the title compounds. The utility of the resulting unnatural amino acids as building blocks to prepare triazole possessing peptidomimetics is also delineated.     

Studies on the putative role ofγ-glutamyl transpeptidase in intestinal transport of amino acids in Atlantic salmon

Summary The -glutamyl cycle is considered to function in the membrane transport of amino acids, particularly glutamine and cysteine. When groups of Atlantic salmon were fed either a control diet containing 45% crude protein or an amino acid diet (of similar overall amino acid composition but containing elevated levels of glutamine and cysteine) for 16 weeks, weight gains were significantly greater in the former group than in those given the amino acid diet. There were no significant differences between treatments in -glutamyl transpeptidase (GT) activity in the proximal intestine; in distal intestine there was significantly more activity in control fish. Mean levels of GSH were higher in tissues (pyloric caeca, distal intestine and kidney) of amino acid diet fish than in those of control fish. Glutamine was less effective as a -glutamyl acceptor than several other amino acids when tested with salmon caecal GT. There were no morphological adaptations to the two feeds. Nutrient uptake studies showed an increased uptake of glutamine, but decreased uptakes of proline and methionine in proximal intestine of salmon fed amino acid diet. Much the greater part of the glutamine uptake, even at high concentrations was shown to be by Na⁺ dependent processes. There is no evidence that GT itself is Na⁺ dependent. The results do not support the view that the -glutamyl cycle and GT in particular are involved in the transport of amino acids in the intestine and are discussed in this context.Abbreviations GT -glutamayl transpeptidase - GSH reduced glutathione     

Employment of gas—liquid chromatography for the analysis of collagen amino acids in biopsy tissue

In this paper, gas—liquid chromatography, adapted for the determination of collagen amino acids, is described. This technique was attractive for its sensitivity in that only a small amount of protein such as in 0.5 mg of tissue, especially as obtained from biopsy tissue, was needed for the separation and determination of proline (Pro), 4-hydroxyproline (4-Hyp), 3-hydroxyproline (3-Hyp), lysine (Lys), hydroxylysine (Hyl) and ?-hydroxynorleucine (?-OH-Norleu), the characteristic amino acids of collagen. Thus, without purification of collagen, by determining the ratio Hyl/4-Hyp and 4-Hyp/Pro it was possible to determine some anomalies in the collagen content of biopsy tissue (skin or liver). The ratio Hyl/4-Hyp allows an estimation of the lack of hydroxylation of polypeptidic lysine as in the Ehlers-Danlos syndrome type VI; and the ratio 4-Hyp/Pro allows measurement of variations in collagen content in relation to protein, especially in the liver, as in alcoholic cirrhosis.     

An information-theoretic classification of amino acids for the assessment of interfaces in protein–protein docking

Docking represents a versatile and powerful method to predict the geometry of protein–protein complexes. However, despite significant methodical advances, the identification of good docking solutions among a large number of false solutions still remains a difficult task. We have previously demonstrated that the formalism of mutual information (MI) from information theory can be adapted to protein docking, and we have now extended this approach to enhance its robustness and applicability. A large dataset consisting of 22,934 docking decoys derived from 203 different protein–protein complexes was used for an MI-based optimization of reduced amino acid alphabets representing the protein–protein interfaces. This optimization relied on a clustering analysis that allows one to estimate the mutual information of whole amino acid alphabets by considering all structural features simultaneously, rather than by treating them individually. This clustering approach is fast and can be applied in a similar fashion to the generation of reduced alphabets for other biological problems like fold recognition, sequence data mining, or secondary structure prediction. The reduced alphabets derived from the present work were converted into a scoring function for the evaluation of docking solutions, which is available for public use via the web service score-MI: http://score-MI.biochem.uni-erlangen.de     

Stereospecific synthesis of α-methylated amino acids

Summary. Both 2,5-trans and 2,5-cis disubstituted 2-tert-butyl-5-(indol-3-yl)methylimidazolidin-4-ones were synthesised and their enolates were prepared using LDA. While the enolate of the 2,5-trans disubstituted derivative could not be methylated, the enolate of the cis-2,5-disubstituted derivative was successfully methylated with methyl iodide to a product which on hydrolysis gave enantiomerically pure α-methyl-L-tryptophan. Received October 31, 1998, Accepted July 23, 1999     

Anion–π interactions in complexes of proteins and halogen-containing amino acids

We analyzed the potential influence of anion–π interactions on the stability of complexes of proteins and halogen-containing non-natural amino acids. Anion–π interactions are distance and orientation dependent and our ab initio calculations showed that their energy can be lower than ?8 kcal mol^?1, while most of their interaction energies lie in the range from ?1 to ?4 kcal mol^?1. About 20 % of these interactions were found to be repulsive. We have observed that Tyr has the highest occurrence among the aromatic residues involved in anion–π interactions, while His made the least contribution. Furthermore, our study showed that 67 % of total interactions in the dataset are multiple anion–π interactions. Most of the amino acid residues involved in anion–π interactions tend to be buried in the solvent-excluded environment. The majority of the anion–π interacting residues are located in regions with helical secondary structure. Analysis of stabilization centers for these complexes showed that all of the six residues capable of anion–π interactions are important in locating one or more of such centers. We found that anion–π interacting residues are sometimes involved in simultaneous interactions with halogens as well. With all that in mind, we can conclude that the anion–π interactions can show significant influence on molecular organization and on the structural stability of the complexes of proteins and halogen-containing non-natural amino acids. Their influence should not be neglected in supramolecular chemistry and crystal engineering fields as well.     

Are phloem amino acids involved in the shoot to root control of NO3- uptake in Ricinus communis plants?

The putative role of phloem amino acids as negative feedback signals for root NO3^- uptake was investigated in Ricinus communis L. The NO3^--grown plants were subjected to N-deficiency due either to complete N-deprivation, or to localized N-deprivation on one side of a split-root system. In comparison with controls, complete N-deprivation resulted in a transient increase in ¹⁵NO3^- influx, and in profound changes in downward phloem transport of amino acids. Total amino acid concentration in the phloem sap decreased by 40%, but responses markedly differed between the individual amino acids. Concentrations of Gln and Ser were rapidly lowered by 50%, while those of Val, Phe, Leu, and Ile displayed a marked increase. Localized N-deprivation on one side of the split root system also resulted in the up-regulation of ¹⁵NO3^- influx in the roots still supplied with NO3^-. However, the amino acid composition of the phloem sap directed to these roots was not modified by the treatment, and remained similar to that in N-sufficient control plants. Only amino acid transport to the N-deprived roots was affected as observed in response to complete N-deprivation. The results from split-root plants indicate that the response of root NO3^- influx to N-deficiency is controlled by shoot-borne regulatory signals, and provide a case study where these signals are not related to a qualitative change or a significant decrease in downward phloem transport of amino acids.     

The effect of amino acids on the C₁₄-sphingosine-triggered germination of Nomuraea rileyi, and surface amino acids on Spodoptera litura fabricius

D-erythro-C??-Sphingosine (C??-Sph) accelerated the germination of Nomuraea rileyi in a solution containing peptone, but activity declined to a large degree in water. This suggests the presence of a co-factor in C??-Sph-triggered germination. Since the main role of peptone is to supply nitrogen constituents, we examined the effects of various nitrogen constituents. It was found that Ala and His were highly effective for C??-Sph-triggered germination.     

Are proteins ideal mixtures of amino acids? Analysis of energy parameter sets

Various existing derivations of the effective potentials of mean force for the two-body interactions between amino acid side chains in proteins are reviewed and compared to each other. The differences between different parameter sets can be traced to the reference state used to define the zero of energy. Depending on the reference state, the transfer free energy or other pseudo-one-body contributions can be present to various extents in two-body parameter sets. It is, however, possible to compare various derivations directly by concentrating on the "excess" energy-a term that describes the difference between a real protein and an ideal solution of amino acids. Furthermore, the number of protein structures available for analysis allows one to check the consistency of the derivation and the errors by comparing parameters derived from various subsets of the whole database. It is shown that pair interaction preferences are very consistent throughout the database. Independently derived parameter sets have correlation coefficients on the order of 0.8, with the mean difference between equivalent entries of 0.1 kT. Also, the low-quality (low resolution, little or no refinement) structures show similar regularities. There are, however, large differences between interaction parameters derived on the basis of crystallographic structures and structures obtained by the NMR refinement. The origin of the latter difference is not yet understood.     

What Drives the Occurrence of the Melioidosis Bacterium Burkholderia pseudomallei in Domestic Gardens?

Melioidosis is an often fatal infectious disease affecting humans and animals in tropical regions and is caused by the saprophytic environmental bacterium Burkholderia pseudomallei. Domestic gardens are not only a common source of exposure to soil and thus to B. pseudomallei, but they also have been found to contain more B. pseudomallei than other environments. In this study we addressed whether anthropogenic manipulations common to gardens such as irrigation or fertilizers change the occurrence of B. pseudomallei. We conducted a soil microcosm experiment with a range of fertilizers and soil types as well as a longitudinal interventional study over three years on an experimental fertilized field site in an area naturally positive for B. pseudomallei. Irrigation was the only consistent treatment to increase B. pseudomallei occurrence over time. The effects of fertilizers upon these bacteria depended on soil texture, physicochemical soil properties and biotic factors. Nitrates and urea increased B. pseudomallei load in sand while phosphates had a positive effect in clay. The high buffering and cation exchange capacities of organic material found in a commercial potting mix led to a marked increase in soil salinity with no survival of B. pseudomallei after four weeks in the potting mix sampled. Imported grasses were also associated with B. pseudomallei occurrence in a multivariate model. With increasing population density in endemic areas these findings inform the identification of areas in the anthropogenic environment with increased risk of exposure to B. pseudomallei.