Silk Peptide Research Articles

Solution behavior of synthetic silk peptides and modified recombinant silk proteins

Spider dragline silk from Nephila clavipes possesses impressive mechanical properties derived in part from repetitive primary sequence containing polyalanine regions that self-assemble into crystalline β-sheets. In the present study, we have sought to understand more details of redox responses related to conformational transitions of modified silk peptides and a recombinant protein containing encoded methionine triggers. Regardless of the position of the methionine trigger relative to the polyalanine domain, chemical oxidation was rapid and slight increases in the α-helical structure and decreases in the β-sheet and random coil content were observed by CD and FTIR in the assembled silk-like peptides and the recombinant protein. CD results indicated that the decrease in β-sheet and random coil conformations, coupled with the increase in helical content during oxidation, occurred during the first 30 min of the reaction. No further conformational changes occurred after this time and the response was independent of methionine trigger location relative to the penta-alanine domain. These results were confirmed with fluorescence studies. The design, processing and utility of these modified redox triggered silk-like peptides and proteins suggest a range of potential utility, from biomaterials to engineered surface coatings with chemically alterable secondary structure and, thus, properties.

Raman Spectroscopic Evidence for Side-Chain Unfolding in Spider Dragline Silk under Tensile Deformation

AbstractIn-situ Ramanspectra were collected on the N. clavipes spider dragline silk under a tensile deformation rate of 15mm/min. The most prominent features on the spectra were due to those bands near 1100 cm-1, which present as a sensitive probe to structural changes associated with side-chains of silk peptide. A downshift of Raman bands at 1095 cm-1 and 1089 cm-1 was detected with increasing strain. Furthermore, an increase in the intensity of the Raman band at 1062 cm-1 due to the vibration of trans structure without lateral coupling was prominent at certain strain levels. This was interpreted in terms of a morphology transition from the random configuration to the trans conformation modulated by the reorganization of the hydrogen bonding among the side-chain.

Determining dihedral angles and local structure in silk peptide by 13C-2H REDOR.

13C-2H REDOR NMR experiments were performed on 30-residue (AlaGly)15 silk I mimics of Bombyx mori silk fibroin to gain structural details about the elusive structure of the silk I conformation. 13C,2H-labeling strategies are illustrated for measuring individual dihedral angles in peptides and for determining local structure by REDOR. A major turn of type II character is found in the region Gly(14)-Ala(17).

Synthesis and characterization of chitosan–poly(acrylic acid) nanoparticles

Chitosan (CS)–poly(acrylic acid) (PAA) complex nanoparticles, which are well dispersed and stable in aqueous solution, have been prepared by template polymerization of acrylic acid (AA) in chitosan solution. The physicochemical properties of nanoparticles were investigated by using size exclusion chromatography, FT-IR, dynamic light scattering, transmission electron microscope and zeta potential. It was found that the molecular weight of PAA in nanoparticles increased with the increase of molecular weight of CS, indicating that the polymerization of acrylic acid in the chitosan solution was a template polymerization. It was also found that the prepared nanoparticles carried a positive charge and showed the size in the range from 50 to 400 nm. The surface structure and zeta potential of nanoparticles can be controlled by different preparation processes. The experiment of in vitro silk peptide (SP) release showed that these nanoparticles provided a continuous release of the entrapped SP for 10 days, and the release behavior was influenced by the pH value of the medium.

Conformational Transitions in Model Silk Peptides

Protein structural transitions and β-sheet formation are a common problem both in vivo and in vitro and are of critical relevance in disparate areas such as protein processing and β-amyloid and prion behavior. Silks provide a “databank” of well-characterized polymorphic sequences, acting as a window onto structural transitions. Peptides with conformationally polymorphic silk-like sequences, expected to exhibit an intractable β-sheet form, were characterized using Fourier transform infrared spectroscopy, circular dichroism, and electron diffraction. Polymorphs resembling the silk I, silk II ( β-sheet), and silk III (threefold polyglycine II-like helix) crystal structures were identified for the peptide fibroin C (GAGAGS repetitive sequence). Two peptides based on silk amorphous sequences, fibroin A (GAGAGY) and fibroin V (GDVGGAGATGGS), crystallized as silk I under most conditions. Methanol treatment of fibroin A resulted in a gradual transition from silk I to silk II, with an intermediate state involving a high proportion of β-turns. Attenuated total reflectance Fourier transform infrared spectroscopy has been used to observe conformational changes as the peptides adsorb from solution onto a hydrophobic surface. Fibroin C has a β-strand structure in solution but adopts a silk I-like structure upon adsorption, which when dried on the ZnSe crystal contains silk III crystallites.