Large Self-Assembled Peptide Fibers
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Large Self-Assembled Peptide Fibers Justin R. Barone and Ahmad Athamneh Biological Systems Engineering Dept., Virginia Tech, 303 Seitz Hall (0303), Blacksburg, VA 24061, U.S.A. ABSTRACT Many systems, including peptide systems, have been identified that self-assemble into nanometer sized structures. However, continued self-assembly to the macroscopic scale has remained elusive even though nature routinely does it. Here, a unique hierarchical peptide self-assembly process is described from the nanometer to the micrometer scale. INTRODUCTION Nature relies on hierarchical self-assembly from the molecular to the macroscopic scale to create sophisticated functional materials1. There are major efforts underway to study protein selfassembly for various medical2 and industrial reasons3, 4. Despite huge progress, studies have focused on nanoscale self-assembly but the crossover to the macroscopic scale remains a challenge. Furthermore, studies have mainly relied on self-assembly under non-natural conditions, even though in nature most structures assemble under physiological or near physiological conditions. Here, we report self-assembly of macroscopic fibers from tryptic peptides under near physiological conditions. The multiscale hierarchical self-assembly was a cooperative process involving hydrophobic -strands and -helical peptides. We modified the macroscopic properties by altering the ratio of constituent peptides. The ability to take, and potentially control, self-assembly beyond the nanoscale will have significant implications on design and fabrication of new functional materials. EXPERIMENT Proteolysis. Wheat gluten (VWR International) was incubated in a 2.5% w/w aqueous suspension with trypsin (Sigma Aldrich) at 1:1000 enzyme-to-substrate ratio by weight. The solution was maintained at 37 °C and pH 8 by manual addition of 1.0 M sodium hydroxide with continuous gentle stirring. Control reactions were carried out under identical conditions without adding trypsin. Aliquots were frequently taken and dried under the fume hood at room temperature for further analysis. Myoglobin (Sigma Aldrich) and gliadin (TCI America) were hydrolyzed together under the same experimental conditions but 1:100 enzyme-to-substrate ratio while varying gliadin-to-myoglobin ratio w/w. Fibers formed in the solution within 48 h. Fourier Transform Infrared (FTIR) spectroscopy. Spectra of dried samples were obtained using a Thermo Electron Nicolet 6700 Spectrometer with a Smart Orbit ATR diamond cell. The spectra were collected using 256 scans at 4 cm-1 resolution from 4000-525 cm-1. A blank was run between each sample to ensure that the cell was clean and a background was collected prior to each run. Deconvolution and fitting of the amide I band was performed using OMNIC v 7.3 software. The spectral range 17001600 cm-1 was fitted with Gaussian/Lorentzian peaks. The number and position of peaks were determined by the automatic peak finding feature of the
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OMNIC program using low sensitivity and full width at half-height of 3.857. All spectr
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