Fiber Formation of a Synthetic Peptide Derived from Spider Dragline of Nephila Clavata

Abstract

Spider dragline is a high performance biopolymer with exceptional mechanical properties. It is 5 times stronger than stainless wire, and high tensile strength and elasticity. The dragline is formed in the major ampullate gland of Nephila clavata and is composed of two major silk proteins, spidroin I and II. Our previous study suggested that the synthetic peptide derived from Nephila clavata forms large-sized fibers. However, the mechanism associated with spinning and the structure of the dragline silk protein remains to be studied in detail.To further investigate the relationship between structure and fiber formation, the fiber forming regions of spidroin were predicted, based on the hydrophobicity of individual amino acid residues. The candidate peptides were chemically synthesized by a solid-phase method, purified by reversed-phase HPLC, and the structures confirmed by MALD-TOF/MS analysis.The conditions for fiber formation for the candidate peptides were screened in a series of aqueous and organic solvents. Large-sized fibers were obtained when an organic solvent was used, under acidic conditions. However, the peptide was not able to form fibers under basic conditions.To obtain structural information on fiber formation, Circular Dichroism measurements of the synthetic spider peptides were performed. The results suggested that the formation of a β-sheet structure is required for fiber formation of the spider peptide.To characterize the peptide fibers, Dynamic laser light-scattering measurements were carried out under several conditions. The results indicated that the synthetic peptide formed a homogeneous oligomer at the initial time and moved to a large-sized oligomer at the later time.In conclusion, the fiber formation of the synthetic spider peptide occurs in organic solvents under acidic conditions and the synthetic peptide forms a homogeneous large-sized oligomer. The results will be discussed in this paper.