Silk from Indian paper wasp: Structure prediction and secondary conformational analysis

Well-defined nanostructural control from biological motifs is gaining attention among materials scientists. We are reporting that the β-sheet structure of L-polyalanine plays a critical role in developing a fibrous nanostructure as well as the sol-to-gel transition of amphiphilic poly(ethylene glycol)-L/or DL-polyalanine diblock copolymers. L-isomers underwent transitions from random coils to β-sheets, and to nanofibers as the polymer concentration increased, whereas the DL-isomer remained as a random coil structure without developing any specific nanostructure. At high polymer concentrations, the aqueous polymer solutions underwent a sol-to-gel transition as the temperature increased, a so called reverse thermal gelation. The L-isomer with a preassembled β-sheet secondary structure facilitates the sol-to-gel transition rather than the DL-isomer with a random coil structure. Thus, only the L-isomer showed a sol-to-gel transition in the physiologically important range of 20–40 °C. This report provides fundamental information on the relationship between hierarchical structures of polypeptides and the thermosensitive sol-gel transition of the polypeptide aqueous solution.

Folic acid complexes with human and bovine serum albumins

Bombyx mandarina silk fibers, as a precious resource of wild silk fibers, have some different characteristics to Bombyx mori silk fibers. To make a better use of this precious green material in various fields, it is necessary to investigate the characteristics of the fibers. In this research, the structure and properties of Bombyx mori silk fiber, Hybrid silk fiber, and Bombyx mandarina silk fiber are studied and analyzed. In terms of secondary structure, β-sheet structures are dominant in all three fibers while random coil and α-helix structures account for smaller portions of the fibers. Bombyx mandarina silk fiber exhibits a characteristic of amino acid distribution where the content of glycine is higher than that of alanine. The further analysis indicates the breaking strength of B. mandarina silk fibers is superior to that of B. mori silk fiber although Bombyx mandarina silk fiber is finer than Bombyx mori silk fiber. Our investigations provide a significant guide in the development and utilization of these precious silk resources, and Bombyx mandarina and Hybrid silk fibers show good potential for application in the same fields as Bombyx mori silk fibers.

Secondary structure of three amyloid β-peptides [Aβ(1–28), Aβ(1–40) and Aβ(1–42)] in the solid state was respectively determined by Fourier transform infrared (FT-IR) microspec- troscopy. Their thermal-dependent structural transformation were also investigated by FT- IR microspectroscopy equipped with a thermal analyzer. The present result demonstrates that the solid-state Aβ(1–28), Aβ(1–40) and Aβ(1–42) peptides showed a significant IR spectral difference in the amide I and II bands. The secondary conformation of Aβ(1–28) peptide was the combination of major β-sheet and minor α-helix with little random coil structures, but Aβ(1–40) peptide showed the co-existence of major β-sheet and minor random coil with little α-helix structures. Aβ(1–42) peptide mainly consisted of the predominant β-sheet structure. Although the intact Aβ(1–28), Aβ(1–40) or Aβ(1–42) peptide exhibits a different secondary structure, a similar β-conformation may form after thermal treatment. A thermal- dependent transition was found for solid Aβ(1–28) and Aβ(1–40) peptides near 40° C and 45° C, respectively. There was no transition temperature for solid Aβ(1–42) peptide, however, due to only a very little level of α-helix and random coil structure containing in the solid Aβ(1–42) peptide. The thermal denaturation plays an important role in the structural transformation from α-helix/random coil to β-sheet.

Binding of antitumor tamoxifen and its metabolites 4-hydroxytamoxifen and endoxifen to human serum albumin

Elastin is the principal protein found in the elastic fibers of vertebrate tissues, and the water within these fibers plays a crucial role in preserving the structure and function of this hydrophobic protein. Soluble elastin was successfully obtained by repeatedly treating insoluble elastin, extracted from pig aorta, with oxalic acid. Solid-state NMR analysis was performed on the soluble elastin, focusing on conformation-dependent chemical shifts of alanine residues. This analysis revealed that cross-linked alanine residues exhibited both α-helix and random coil structures in the dry state. In contrast, the hydrated state favored random coil structures, with some distorted helices possibly present, indicating that the cross-linked configuration is relatively unstable. Similar conformational changes were observed in insoluble elastin, mirroring those found in the soluble form. Additionally, when the soluble elastin was re-cross-linked using 1,12-dodecanedicarboxylic acid and 4-hydroxyphenyl dimethylsulfonium methylsulfate, it retained a mixture of α-helix and random coil structures in the dry state. Remarkably, in the hydrated state, α-helix structures were more prominently preserved alongside random coils. These structural changes corresponded with increased stiffness of molecular chains in the hydrophobic regions compared to their state prior to re-cross-linking, even under hydrated conditions.

Conformational study of globulin from rice ( Oryza sativa) seeds by Fourier-transform infrared spectroscopy

Poly(ethylene glycol)–poly(alanine-co-phenylalanine) (PEG–PAF) block copolymers with similar molecular weights were synthesized to investigate the effect of the partial incorporation of D-alanine into PEG-L-PAF. The ratio of L-alanine to D-alanine of the polymer varied over 100/0, 80/20, 60/40, 50/50, and 0/100. Circular dichroism and FTIR spectra indicated that the PEG–PAFs with the mixed composition of L-alanine and D-alanine exhibited dominantly random coil structures, whereas the PEG–PAF with the enantiomeric alanine (100/0 or 0/100) exhibited right-handed or left-handed α-helical structures as well as β-sheet structures, respectively. Dynamic light scattering of the polymer aqueous solution indicated that the size of nanoassemblies significantly decreased as a result of the partial incorporation of D-alanine into PEG-L-PAF. The most probable diameters were 20–40 nm and 80–105 nm for the PEG–PAFs with a mixed composition (L-alanine/D-alanine ratios of 80/20, 60/40, and 50/50) and an enantiomeric composition (L-alanine/D-alanine ratios of 0/100 and 100/0), respectively. As the temperature increased, the relative β-sheet content decreased for PEG–PAF with the enantiomeric alanine, while there was no significant change in random coil structures of PEG–PAFs with a mixed composition. 13C-NMR spectra suggest the dehydration and decrease in molecular motion of PEG during the sol-to-gel transition of PEG–PAF. Through the partial incorporation of D-alanine into PEG-L-PAF, thermogelling behaviour was also observed at much higher temperatures and concentrations due to the difference in the secondary structure and nanoassembly of the polymers. The enzymatic degradability of PEG–PAF also decreased as a result of the partial incorporation of D-alanine into PEG-L-PAF. The paper suggests that partial incorporation of D-alanine into an L-polypeptide block copolymer can be a useful method in designing a biodegradable material as well as controlling nanoassemblies of the polymer.

Trehalose inhibits fibrillation of A53T mutant alpha-synuclein and disaggregates existing fibrils

The poly-l-lysine-functionalized gold nanoparticle (PLL-GNP) was found to undergo reversible assembly/disassembly in the range of pH from 6.5 to 11.0 at room temperature. At a high pH value, the deprotonated lysine residues allow the formation of α-helix and β-sheet structures at the expense of a part of random coil and β-turn structures, thus inducing the assembly of GNPs. With a decrease of pH to 6.5, the assembly of GNPs is disrupted due to the conversion of the α-helix and β-sheet back into the random and β-turn. It is identified that the formation/collapse of an antiparallel β-sheet structure among PLL chains from adjacent GNPs is responsible for reversible pH-dependent assembly/disassembly of GNPs. Since the conformation-induced assembly/disassembly process of the PLL-GNP can be well recognized by a shift of the surface plasmon resonance band of the GNP and the color change of the solution, this study presents the possibility of following the conformation change of a peptide by monitoring the spectr...

Dialysis is the rate-limiting step in the preparation of aqueous silk fibroin (SF) solution. However, the traditional practice of dialyzing SF solution for at least 48 h to remove LiBr is not based on empirical evidence. The aim of the present study was to systematically measure LiBr content in SF solutions dialyzed for varying lengths of time and assess the potential toxicity of residual lithium ions in cells. Complete removal of lithium ions was not achieved even after 72 h of dialysis, with a residual lithium ion content in the solution of 22.85 mg/l. SF films prepared from solutions dialyzed for 8 and 24 h had predominantly random coil or b-sheet structures, respectively. The residual lithium had little cytotoxicity in NIH3T3 fibroblast cells, but viability was compromised in cells grown on SF film prepared from solution dialyzed for 24 h.

FT-IR spectroscopy has been applied to study the secondary structure of the major coat protein of Pf1 and M13 as present in the phage and reconstituted in DOPG and mixed DOPC/DOPG (4/1) bilayers. Infrared absorbance spectra of the samples were examined in dehydrated films and in suspensions of D2O and H2O. The secondary structure of the coat protein is investigated by second-derivative analysis, Fourier self-deconvolution, and curve fitting of the infrared bands in the amide I region (1600-1700 cm-1). It is found that, in dehydrated films of Pf1 and M13 phage, the amide I region contains three bands located at about 1633, 1657, and 1683 cm-1, that are assigned to hydrogen-bonded turn, alpha-helix/random coil, and non-hydrogen-bonded turn, respectively. From a comparison of the infrared spectra in dehydrated film with those in aqueous suspension, the percentages of secondary structure were found with an accuracy of about +/- 5%. For the coat protein of Pf1 phage, the FT-IR quantification gives 69% alpha-helix conformation, 19% turn structure, and 12% random coil structure. For Pf1 coat protein in the membrane-embedded state, the amount of alpha-helix is 57%, whereas 42% is in a turn structure and 1% in a random coil structure. The same assignment strategy was used for the analysis of the data obtained for M13 coat protein reconstitution into phospholipid systems. For M13 coat protein in the phage, this gives 75% alpha-helix conformation, 21% turn structure, and 4% random coil structure.(ABSTRACT TRUNCATED AT 250 WORDS)

4 - Regenerated silk fibers

Effect of oil extraction methods on walnut oil quality characteristics and the functional properties of walnut protein isolate

In the present work, an attempt has been made to analyze the arsenic induced biochemical changes in the gill tissues of freshwater fish Labeo rohita using Fourier transform infrared (FT-IR) spectroscopy. The FT-IR spectrum of gill tissue is quite complex and contains several bands arising from the contribution of different functional groups belonging to lipids, proteins, and others. FT-IR spectra reveal significant differences in absorbance intensities and areas between the control and arsenic intoxicated gill tissues. The amide I and II peaks observed at 1654 and 1542 cm−1 suggest that the protein is dominated by α-helical structure in the gill tissues. The result further shows that due to arsenic intoxication, α-helical structure decreases significantly with an increase in β-sheet and random coil structures. In conclusion, the present study shows that the gill tissues are vulnerable to arsenic intoxication. The result further suggests that arsenic intoxication induces significant alteration on the major biochemical constituents such as lipids, proteins and nucleic acids, which can be easily evidenced by FT-IR spectroscopy.