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Research Paper

Mechanistic Study of Self-Assembling Peptide RADA16-I in Formation of Nanofibers and Hydrogels

[+] Author and Article Information
Hangyu Zhang, Hanlin Luo

Institute for Nanobiomedical Technology and Membrane Biology, Sichuan University, No.1, Ke Yuan 4th Street, Gao Peng Road, Chengdu, 610041 Sichuan, China

Xiaojun Zhao1

Institute for Nanobiomedical Technology and Membrane Biology, Sichuan University, No.1, Ke Yuan 4th Street, Gao Peng Road, Chengdu, 610041 Sichuan, China; Center for Biomedical Engineering, NE47-378, Massachusetts Institute of Technology, Cambridge, MA 02139-4307xiaojunz@mit.edu

1

Corresponding author.

J. Nanotechnol. Eng. Med 1(1), 011007 (Oct 29, 2009) (6 pages) doi:10.1115/1.4000301 History: Received September 23, 2009; Revised September 23, 2009; Published October 29, 2009

The biophysical and biochemical properties of RADA16-I, the representative of a class of self-assembling peptides, were studied to elucidate the molecular mechanism of nanofiber and hydrogel formations. We found that self-assembly occurs in the solution at low pH (pH 4), rather than the popular belief that it occurs in the physiological environment. Actually, the peptide lost its β-sheet structure and formed irregular aggregates in the condition around pH 7. Our results demonstrated that the extended conformation of peptide backbone caused by the electrostatic repulsive force in acid solution is crucial for the peptide to self-assemble into nanofibers. Importantly, we have proposed a mechanism for the peptide to form nanofiber hydrogel in the physiological condition, which is not propitious for nanofiber formation. Hypothetically, it is by virtue of the tendency of fibers to collapse and form irregular aggregates at pH 7 that we could obtain stable hydrogels by introducing phosphate buffered saline into the system.

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Figure 3

Chemical structures of RADA16-I in the solution of pH 4 (a) and pH 7 (b). (a) The peptide was mainly positively charged. The four alkaline arginine side chains are ionized to positive charges, while four acidic aspartic side chains are hardly ionized and almost neutrally charged. (b) The peptide contained alternating positive and negative charges.

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Figure 4

The typical AFM morphological images of 100 μM peptide RADA16-I at different conditions: (a) in pure water (pH 4), (b) in PBS (pH 7.1), and (c) in 0.9% NaCl

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Figure 5

Frequency sweep data on 1 wt % RADA16-I (a) in pure water without triggering; (b) triggered by PBS or NaOH to form hydrogel

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Figure 2

The effect of different solutions on secondary structure of peptide RADA16-I (0.1 mM). All the spectra were obtained at 25°C after incubation overnight at 4°C, and peptide RADA16-I exhibited a typical β-sheet structure (minimum at ∼216 nm, maximum at 196 nm) in pure water. The color patterns and different solutions are shown in the frame.

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Figure 1

Schematic representation of three-dimensional molecular model of RADA16-I. Carbon atoms are white, oxygen atoms are red, nitrogen atoms are blue, and hydrogen atoms are gray. The dimensions are about 5 nm in length, 1.3 nm in height, and 0.8 nm in width (32).

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