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ABSTRACTDeep-sea Shewanella violacea5′-nucleotidase (SVNTase) activity exhibited higher NaCl tolerance than that of a shallow-sea Shewanella amazonensishomologue (SANTase), the sequence identity between them being 70.4%. Here, SVNTase exhibited higher activity than SANTase with various inorganic salts, similar to the difference in their NaCl tolerance. In contrast, SVNTase activity decreased with various organic solvents, while SANTase activity was retained with the same concentrations of the solvents. Therefore, SVNTase is more robust than SANTase with inorganic salts, but more vulnerable with organic solvents. As to protein stability, SANTase was more stable against organic solvents and heat than SVNTase, which correlated with the differences in their enzymatic activities. We also found that SANTase retained higher activity for three weeks than SVNTase did in the presence of glycerol. These findings will facilitate further application of these enzymes as appropriate biological catalysts under various harsh conditions.Abbreviations:NTase: 5′-nucleotidase; SANTase: Shewanella amazonensis5′-nucleotidase; SVNTase: Shewanella violacea5′-nucleotidase; CD: circular dichroism

The application of marine resources, instead of fossil fuels, for biomass production is important for building a sustainable society. Seaweed is valuable as a source of marine biomass for producing biofuels such as ethanol, and can be used in various fields. Alginate is an anionic polysaccharide that forms the main component of brown algae. Various alginate lyases (e.g. exo- and endo-types and oligoalginate lyase) are generally used to degrade alginate. We herein describe a novel alginate lyase, AlgC-PL7, which belongs to the polysaccharide lyase 7 family. AlgC-PL7 was isolated from the halophilic Gram-negative bacterium Cobetiasp. NAP1 collected from the brown algae Padina arborescensHolmes. The optimal temperature and pH for AlgC-PL7 activity were 45 °C and 8, respectively. Additionally, AlgC-PL7 was thermostable and salt-tolerant, exhibited broad substrate specificity, and degraded alginate into monosaccharides. Therefore, AlgC-PL7 is a promising enzyme for the production of biofuels.

We systematically study the relationship between the ultrasonically induced aggregation behavior of amyloid $\beta_{1{\mbox{--}}40}$ peptide and acoustic pressures to clarify the dominant mechanism of the aggregation. With ultrasonic irradiation, the thioflavin-T (ThT) level of the A$\beta$ solution rises after a lag time, takes a maximum at ${\sim}5$ h, and remains unchanged or decreases. Thus, we monitor the ThT level at 5 h to evaluate the progress of the $\beta$-sheet structure and investigate its correlation with the acoustic pressures of fundamental and harmonics waves. The second-harmonics-wave amplitude shows the highest correlation with the ThT level, indicating the dominant contribution of cavitation bubbles to the fibrillation phenomenon. The influence of solution pH and Ar gas are investigated to identify the aggregation mechanism. As a result, local condensation of the peptide due to the high affinity of hydrophobic residues to the bubble-solution interface causes a highly supersaturated solution, leading to precipitation of $\beta$-sheet-rich nuclei.

Amyloid fibrils are self-assemblies of proteins with an ordered cross-$\beta$ architecture. Because they are associated with serious disorders, understanding their structure and mechanism of fibrillation is important. Irradiation with ultrasonication leads to fragmentation of amyloid fibrils, useful for seeding experiments. Recently, ultrasonication has been found to trigger the spontaneous formation of fibrils in solutions of monomeric amyloidogenic proteins. The results indicate that amyloid fibrillation is similar to the crystallization of solutes from a supersaturated solution. The accelerating effects of ultrasonication on amyloid fibrillation suggest that cavitation microbubbles play a key role in effectively converting the metastable state of supersaturation to the labile state, leading to spontaneous fibrillation. Moreover, ultrasonic irradiation would be promising for a high-throughput screening assay of amyloid fibrillation, advancing the study of supersaturation-limited amyloidogenesis.

Hydrodynamic forces are capable of inducing structural order in dispersed solid phases, and of causing symmetry‐breaking when chiral crystals precipitate from an achiral liquid phase. Until it was observed upon vortex‐assisted fibrillation of insulin, such behavior had been thought to be confined to few unbiological systems. In this paper we are discussing chiroptical properties of two chiral variants of insulin amyloid, termed +ICD and −ICD, which form during the process of chiral bifurcation in vortexed solutions of aggregating insulin. As conventional measurements of circular dichroism of solid, anisotropic substances are particularly vulnerable to overlapping influences of linear birefringence and linear dichroism, we have employed complementary tools including dedicated universal chiroptical spectrophotometer to rule out such artifacts. We propose that the strong chiroptical properties of +ICD and −ICD insulin fibrils are an aspect of genuine superstructural chirality of amyloid fibrils and of powerful excitonic couplings taking place within them. A comparison of thioflavin T complexes with fibrils formed by insulin and polyglutamic acid suggests that the extrinsic Cotton effect stemming from the level of single twisted dye molecules is weaker, although diagnostically useful, and cannot account for the overall magnitude of ICD of the dye bound to ±ICD insulin amyloid. Chirality, 2011. © 2011 Wiley‐Liss, Inc.

Using the peptide hormone glucagon and Aβ(1–40) as model systems, we have sought to elucidate the mechanisms by which fibrils grow and multiply. We here present real-time observations of growing fibrils at a single-fibril level. Growing from preformed seeds, glucagon fibrils were able to generate new fibril ends by continuously branching into new fibrils. To our knowledge, this is the first time amyloid fibril branching has been observed in real-time. Glucagon fibrils formed by branching always grew in the forward direction of the parent fibril with a preferred angle of 35–40°. Furthermore, branching never occurred at the tip of the parent fibril. In contrast, in a previous study by some of us, Aβ(1–40) fibrils grew exclusively by elongation of preformed seeds. Fibrillation kinetics in bulk solution were characterized by light scattering. A growth process with branching, or other processes that generate new ends from existing fibrils, should theoretically give rise to different fibrillation kinetics than growth without such a process. We show that the effect of adding seeds should be particularly different in the two cases. Our light-scattering data on glucagon and Aβ(1–40) confirm this theoretical prediction, demonstrating the central role of fibril-dependent nucleation in amyloid fibril growth

Amyloid fibrils have been a critical subject in recent studies of proteins since they are associated with the pathology of more than 20 serious human diseases. Moreover, a variety of proteins and peptides not related to diseases are able to form amyloid fibrils or amyloid-like structures, implying that amyloid formation is a generic property of polypeptides. Although understanding the structure and formation of amyloid fibrils is crucial, due to the extremely high molecular weight and insolubility of amyloid fibrils, most of the conventional techniques available for soluble proteins are not directly applicable to these fibrils. However, structural studies using solid-state NMR have shown that the basic motif of amyloid fibrils is a -strand-loop--strand conformation often in a parallel -sheet assembly. From the hydrogen/ deuterium exchange of amide protons, amyloid fibrils have been shown to be stabilized by an extensive network of hydrogen bonds substantiating -sheets. Our approach using total internal reflection fluorescence microscopy combined with thioflavin T, an amyloid-specific fluorescence dye, enabled monitoring fibril growth in real-time at single fibril level. On the basis of these various approaches, increasingly convincing models of amyloid structures, their formation and propagation are emerging.