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To better understand the mechanism of inherent salt resistance in Jerusalem artichoke (Helianthus tuberosus L.), physiological and metabolic responses of tubers at the initiation stage of sprouting under different salt stress levels were evaluated in the present study. As a result, 28 metabolites were identified using proton nuclear magnetic resonance (1H-NMR) spectroscopy. Jerusalem artichoke tubers showed minor changes in metabolic response under moderate salt stress when they had not yet sprouted, where metabolism was downregulated at the start of sprouting and then upregulated significantly after plants became autotrophic. However, mild and severe salt stress levels caused different metabolic response patterns. In addition, the accumulation of fructose and sucrose was enhanced by moderate salt stress, while glucose was highly consumed. Aspartate and asparagine showed accelerated accumulation in sprouting Jerusalem artichoke tubers that became autotrophic, suggesting the enhancement of photosynthesis by moderate salt stress. [ABSTRACT FROM AUTHOR]

During our search for novel prenyltransferases, a putative gene ATEG_04218 from Aspergillus terreus raised our attention and was therefore amplified from strain DSM 1958 and expressed in Escherichia coli. Biochemical investigations with the purified recombinant protein and different aromatic substrates in the presence of dimethylallyl diphosphate revealed the acceptance of all the tested tryptophan-containing cyclic dipeptides. Structure elucidation of the main enzyme products by NMR and MS analyses confirmed the attachment of the prenyl moiety to C-7 of the indole ring, proving the identification of a cyclic dipeptide C7-prenyltransferase (CdpC7PT). For some substrates, reversely C3- or N1-prenylated derivatives were identified as minor products. In comparison to the known tryptophan-containing cyclic dipeptide C7-prenyltransferase CTrpPT from Aspergillus oryzae, CdpC7PT showed a much higher substrate flexibility. It also accepted cyclo- l-Tyr- l-Tyr as substrate and catalyzed an O-prenylation at the tyrosyl residue, providing the first example from the dimethylallyltryptophan synthase (DMATS) superfamily with an O-prenyltransferase activity towards dipeptides. Furthermore, products with both C7-prenyl at tryptophanyl and O-prenyl at tyrosyl residue were detected in the reaction mixture of cyclo- l-Trp- l-Tyr. Determination of the kinetic parameters proved that ( S)-benzodiazepinedione consisting of a tryptophanyl and an anthranilyl moiety was accepted as the best substrate with a K value of 204.1 μM and a turnover number of 0.125 s. Cyclo- l-Tyr- l-Tyr was accepted with a K value of 1,411.3 μM and a turnover number of 0.012 s. [ABSTRACT FROM AUTHOR]

Aquatic agriculture in heavy-metal-polluted coastal areas faces major problems due to heavy metal transfer into aquatic organisms, leading to various unexpected changes in nutrition and primary and/or secondary metabolism. In the present study, the dual role of heavy metal copper (Cu) played in the metabolism of photosynthetic organism, the edible seaweed Sargassum fusiforme, was evaluated by characterization of biochemical and metabolic responses using both 1H NMR and GC-MS techniques under acute (47 µM, 1 day) and chronic stress (8 µM, 7 days). Consequently, photosynthesis may be seriously inhibited by acute Cu exposure, resulting in decreasing levels of carbohydrates, e.g., mannitol, the main products of photosynthesis. Ascorbate may play important roles in the antioxidant system, whose content was much more seriously decreased under acute than that under chronic Cu stress. Overall, these results showed differential toxicological responses on metabolite profiles of S. fusiforme subjected to acute and chronic Cu exposures that allowed assessment of impact of Cu on marine organisms. [ABSTRACT FROM AUTHOR]

A fundamental investigation of the biosorption of Cd2+ from aqueous solution by the edible seaweed Sargassum fusiforme was performed under batch conditions. The influences of experimental parameters, such as the initial pH, sorption time, temperature, and initial Cd2+ concentration, on Cd2+ uptake by S. fusiforme were evaluated. The results indicated that the biosorption of Cd2+ depended on the initial Cd2+ concentration, as well as the pH. The uptake of Cd2+ could be described by the Langmuir isotherm model, and both the Langmuir biosorption equilibrium constant and the maximum biosorption capacity of the monolayer decreased with increasing temperature, thereby confirming the exothermic character of the sorption process. The biosorption kinetics follows the pseudo-second-order kinetic model, and intraparticle diffusion is the sole rate-limiting step for the entire biosorption period. These fundamental equilibrium and kinetic results can support further studies to the removal of cadmium from S. fusiforme harvested from cadmium-polluted waters. [ABSTRACT FROM AUTHOR]

A type III polyketide synthase (SfuPKS2) from the edible seaweed Sargassum fusiforme was cloned and biochemically characterized. SfuPKS2 can only accept octanoyl-CoA (C8) and neither other long-chain fatty acyl-CoAs, nor non-fatty acyl-CoAs synthesized in this study as the substrate. In addition, in incubation with octanoyl-CoA, only a single product peak was observed, giving rise to the triketide α-pyrone derivative. To understand the substrate specificity of SfuPKS2, we constructed a structural model and performed docking analysis to reveal amino acid residues critical for enzyme-substrate binding. Putative key residues were then mutated experimentally and the impact on protein function was assessed by incubating the mutant with octanoyl-CoA. We found that key amino acids governing enzyme activity and specificity included Ser171, His236, Phe254, and Ile377. Mutations on these amino acids generally resulted in altered interactions with the substrate and thus the enzyme activity. In summary, our work provided mechanistic insight on how the selectivity toward the substrate is achieved in SfuPKS2. [ABSTRACT FROM AUTHOR]

The intertidal seaweed Sargassum fusiforme shows remarkable tolerances to freshwater immersion, which made experienced cultivators quite convenient to control epiphytic algae that would limit the massive aquaculture production. Here, we performed biochemical and physiological analyses and comparative proteomics to investigate the molecular mechanisms of the hyposalinity-stress-tolerance in S. fusiforme . Our results showed that in the initial period of freshwater immersion, mineral fraction and inorganic anion may be lost much faster than other soluble contents. H 2 O 2 accumulation occurred immediately and the antioxidant system was efficiently activated during freshwater immersion. Comparative proteomic analysis revealed 51 differentially expressed protein spots in S. fusiforme , most of which were enzymes involved in photosynthesis, carbohydrate metabolism and energy metabolism. The one-hour's-freshwater-immersion negatively affected the metabolic activity of S. fusiforme , as synthesis of most key metabolic enzymes were inhibited in varying degrees, with only a few exceptions, e.g., phosphomannomutase, which is related to precursor synthesis of cell wall polysaccharides. Statement of relevance In order to eliminate other wild harmful algae, freshwater or lower salinity of seawater is usually employed to the brown alga Sargassum fusiforme for a short period, indicating its tolerance to hyposalinity stress. Osmotic stress is one of the major abiotic stresses for most algae. As most studies were concerning about the hypersalinity stress, physiological mechanisms of tolerance to hyposalinity stress of algae are not fully understood. This study focuses on responses of the brown alga S. fusiforme to short-term (or acute) hyposalinity stress, using comparative physiology approach combining methods of systems biology including proteomics. Then analyzes the typical physiological characteristics related to osmotic stress and overall physiological metabolic networks to investigate the possible tolerance mechanism of S. fusiforme to hyposalinity stress at physiological level. As an important foundation work, analyzing the effect of hyposalinity stress on the survival of S. fusiforme and its mechanism is helpful to explore the tolerance of algae to abiotic stress. In another aspect, it will also provide the necessary theoretical basis for the freshwater pesticide technology. [ABSTRACT FROM AUTHOR]

Silica nanoparticles have demonstrated broad applicability from wastewater treatment to medicine. By increasing intermolecular interaction of silica precursor, peptides can induce the formation of biosilica usually under neutral and basic but not acidic conditions, and here, they are defined as silica-forming peptides (SFPs). In addition, the silica-forming capability of most putative SFPs has not been evaluated. To address both questions, we developed molecular descriptors to simulate and predict the silica-forming capabilities of SFPs under a wide range of pH values. We used van der Waals and electrostatic interactions as molecular descriptors to probe the physisorption between amino acid residues and proto-silicate. We then performed multiple-dimensional simulations using the canonical R5 peptide and three novel SFPs from the brown alga Sargassum fusiforme. Finally, we experimentally validated the silica-forming capability of the four SFPs at pH values from 4 to 8. Our results showed that the molecular descriptors provide accurate predictions on the adsorption of proto-silicate by SFPs. Thus, the method can be used to screen SFPs that are capable of inducing the formation of silica in a wide pH range more importantly including acidic conditions. [Display omitted] • Molecular descriptors were developed to predict the performance of SFPs. • Silica precipitation of three novel SFPs were evaluated. • The silica precipitation capacity of the four SFPs at pH values 4–8 were validated. [ABSTRACT FROM AUTHOR]

Monodispersed Au decahedral nanocrystals were synthesized and used as seeds to prepare high quality of AuNBs with unusual shape. Penta-fold twinned (PFT) Au nanobipyramids (AuNBs) have outstanding optical properties compared with other PFT Au nanocrystals. The reproducible preparation of the seeds for synthesizing high quality of AuNBs still remains a challenging problem. In this work, we achieved the high-yield and reproducible preparation of small sized Au nanodecahedron (AuND) nanocrystals, and further used them as seeds in a controlled manner to synthesize monodispersed AuNBs and other shaped nanocrystals. The prepared AuNBs have better photothermal conversion performance than other shaped Au nanocrystals. This approach can promote the AuNB-based study and applications in optics, catalysis and therapy. [ABSTRACT FROM AUTHOR]