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. 2018 Oct 22;115(45):11507–11512. doi: 10.1073/pnas.1810203115

Fig. 1.

Fig. 1.

Native L. hesperus MA silk protein diffusion measured by PFG-STE NMR. (A) Gradient echo magnetic resonance image (GRE-MRI, 18.8 T) of 300-µm-thick cross-section slice of the L. hesperus spider abdomen at the coronal cross-section orientation. Red box indicates one of the two MA glands, which were removed by dissection from L. hesperus spiders for all subsequent NMR, DLS, and cryo-TEM analysis. (B–D) PFG-STE NMR data. (B) Self-diffusion coefficient (D) vs. interpulse delay (Δ) for MA silk protein at native gland conditions (concentration ∼35 wt %, pH ∼7). Strong Δ dependence is observed, and the decreasing D as a function of Δ illustrates that diffusion is restricted at native conditions (MSD ∼300 nm). (C) D vs. Δ for the MA silk protein dope following dilution in 4 M urea (concentration ∼10 wt %, 48 h in urea). The Δ dependence is no longer observed, indicating diffusion is not restricted following solubilizing in urea. (D) MA silk protein D measured by PFG-STE NMR as a function of protein concentration in 4 M urea (48 h). The extracted self-diffusion coefficient at infinite dilution is 10.7 × 10−8 cm2/s (rH ∼ 19 nm).