Beating the Heat - Fast Scanning Melts Silk Beta Sheet Crystals

Abstract

Beta-pleated-sheet crystals are among the most stable of protein secondary structures, and are responsible for the remarkable physical properties of many fibrous proteins, such as silk, or proteins forming plaques as in Alzheimer's disease. Previous thinking, and the accepted paradigm, was that beta-pleated-sheet crystals in the dry solid state were so stable they would not melt upon input of heat energy alone. Here we overturn that assumption and demonstrate that beta-pleated-sheet crystals melt directly from the solid state to become random coils, helices, and turns. We use fast scanning chip calorimetry at 2,000 K/s and report the first reversible thermal melting of protein beta-pleated-sheet crystals, exemplified by silk fibroin. The similarity between thermal melting behavior of lamellar crystals of synthetic polymers and beta-pleated-sheet crystals is confirmed. Significance for controlling beta-pleated-sheet content during thermal processing of biomaterials, as well as towards disease therapies, is envisioned based on these new findings.

Papain-Catalyzed Synthesis of Polyglutamate Containing a Nylon Monomer Unit

“…The MALDI-TOF MS spectrum of the peptide from Glu(Et) 2 and nylon 4Me showed peaks with constant intervals of 157 g/mol derived from oligo(GluEt) with DP from 7 to 12 in Figure 2c. Peaks with an interval of 71 g/mol apart from the peaks derived from the oligo(GluEt) were also detected, thus confirming that the nylon 4 unit was introduced into the peptide.…”

“…It is assumed that the acyl moiety of the substrate lies in the large pocket, whereas the leaving group moiety lies in the medium pocket in the catalytic pathway [32]. In this study, Glu(Et) 2 and nylon monomers were considered unable to meet the requirements for the catalytic pathways of proteinase K and lipase.…”

“…In the case of proteinase K, not only the catalytic triad Asp39-His69-Ser224 but also the stable substrate recognition site formed by Ca ions with Asp200, Val177, and Pro175 is required for the catalytic reactions [42]. In the case of lipase, the active center has a catalytic triad of Ser105-His224-Asp187 ,d), and lipase (e,f)-catalyzed product using Glu(Et) 2 and nylon 4Et as substrates. Mass spectra were obtained in linear positive mode using HABA and Na-TFA as the matrix and cationic reagent, respectively.…”

“…Therefore, we used pH 8 and 40˝C for the reaction conditions. As the first step, we performed papain-catalyzed chemoenzymatic synthesis using Glu(Et) 2 and nylon 4Et and then obtained a resultant white precipitate at a yield of 53% based on the initial amounts of the monomers used in the reaction. The MALDI-TOF MS spectrum of the resultant product is shown in Figure 2a.…”

“…For human use of peptides as bulk materials , it would be expected that peptide-based materials would need to be fabricated via a thermal process without any organic solvents [1]. However, peptides do not have a melting point but instead show decomposition during the heating process because the intermolecular hydrogen bonds in peptides are so strong that the intrachain covalent bonds begin to degrade before the melting transition [2]. To design thermally processable peptide materials, we therefore focus on the copolymerization of peptides and unnatural components.…”