Are Spider Silk Proteins a New Class of Intrinsically Disordered Proteins?

Abstract

Spider dragline silk is an outstanding biopolymer with a strength that exceeds steel by weight and a toughness greater than high-performance fibers like Kevlar. For this reason, understanding how a spider converts the gel-like, aqueous protein spinning dope within the major ampullate (MA) gland into a super fiber is of great importance for developing future biomaterials based on spider silk. In this work, the initial state of the silk proteins within Black Widow MA glands was probed with solution-state NMR spectroscopy following isotopic enrichment. 15N relaxation parameters, T1, T2 and 15N-{1H} steady-state NOE were measured for twelve backbone environments at two spectrometer frequencies, 500 and 800 MHz. All observed backbone environments are consistent with MA silk protein dynamics on the fast sub-nanosecond timescale. In addition, the observed conformation-dependent isotropic chemical shifts are consistent with a random coil. Therefore, it is concluded that the repetitive core of spider MA proteins are in an unfolded, highly flexible state in the MA gland. We propose that spider silk proteins can be considered intrinsically disordered proteins prior to fiber formation.