Structural Conformation of Spidroin in Solution:  A Synchrotron Radiation Circular Dichroism Study

Abstract

Spider silk is made and spun in a complex process that tightly controls the conversion from soluble protein to insoluble fiber. The mechanical properties of the silk fiber are modulated to suit the needs of the spider by various factors in the animal's spinning process. In the major ampullate (MA) gland, the silk proteins are secreted and stored in the lumen of the ampulla. A particular structural fold and functional activity is determined by the spidroins' amino acid sequences as well as the gland's environment. The transition from this liquid stage to the solid fiber is thought to involve the conversion of a predominantly unordered structure to a structure rich in beta-sheet as well as the extraction of water. Circular dichroism provides a quick and versatile method for examining the secondary structure of silk solutions and studying the effects of various conditions. Here we present the relatively novel technique of synchrotron radiation based circular dichroism as a tool for investigating biomolecular structures. Specifically we analyze, in a series of example studies on structural transitions induced in liquid silk, the type of information accessible from this technique and any artifacts that might arise in studying self-assembling systems.

Conformational polymorphism, stability and aggregation in spider dragline silks proteins

“…The free energy of spidroin in the absence of alcohols ( G H 2 O ) was found to be approximately the same for TFE and HFIP and is consistent with an independent determination by urea denaturation [17]. However, the m-values differed.…”

“…The control (spidroin in water) underwent a structural transition towards a ␤-sheet rich state. A possible mechanism is discussed elsewhere [17]. At SDS concentration between 0.1 and 4 mM we observed the gradual formation of ␤-sheet rich structures from both Silk A (0.1 mM SDS) and Silk C (2.5-4 mM SDS) initial state.…”

Structure of silk by raman spectromicroscopy: From the spinning glands to the fibers

“…[73][74][75][76] The spectrum is also comparable to that obtained for the in vitro dissolution of recombinant MaSp1 and MaSp2 proteins. The conformation of the spinning dope that has flowed out of the gland is basically identical to the native silk contained in the sac of the gland, and is slightly affected by dehydration.…”

Modular peptides from the thermoplastic squid sucker ring teeth form amyloid-like cross-β supramolecular networks

“…As the pH increases and microfibers are formed from the solution, the concentration of peptide in solution decreases over time (Figure 4), with residual peptides in solution transitioning toward β-sheets structure. Interestingly, this time-dependent evolution of CD spectra is strongly reminiscent to that reported for silk fibroins, [81] where an overall CD signature resembling those measured here for the Ala-rich peptides ( Figure 4 for A1 and A2 peptides) has been reported, and where a strong decrease in ellipticity a few days after initial incubation has also been attributed to a decrease in protein concentration in solution. Furthermore, fibroin conformation has been shown to be strongly pH-dependent, [30] with β-sheet content increasing with pH.…”