Role of Polyalanine Domains in β‐Sheet Formation in Spider Silk Block Copolymers

Abstract

Genetically engineered spider silk-like block copolymers were studied to determine the influence of polyalanine domain size on secondary structure. The role of polyalanine block distribution on beta-sheet formation was explored using FT-IR and WAXS. The number of polyalanine blocks had a direct effect on the formation of crystalline beta-sheets, reflected in the change in crystallinity index as the blocks of polyalanines increased. WAXS analysis confirmed the crystalline nature of the sample with the largest number of polyalanine blocks. This approach provides a platform for further exploration of the role of specific amino acid chemistries in regulating the assembly of beta-sheet secondary structures, leading to options to regulate material properties through manipulation of this key component in spider silks.

Effect of sequence features on assembly of spider silk block copolymers

“…The amide I vibration is generally not affected by the nature of the side chains; therefore, it is most commonly used for analysis of secondary structure. Characteristic assignments of distinct peaks for spider silk were made in accordance with previously published reports (Krishnaji et al, 2013; Rabotyagova et al, 2010). After deconvolution, several characteristic peaks were observed.…”

“…The frequency from 1700 to 1400 cm −1 contains the most important amide I and amide II regions [49]. The amide I band has strong absorption at 1700–1600 cm −1 (Monti et al, 1998), from the C=O stretching vibration (80%) with minor contributions from N-H in plane bending, out of phase C-N stretching vibrations, and C-N deformation (Hu et al, 2006; Rabotyagova et al, 2010). The amide I vibration is generally not affected by the nature of the side chains; therefore, it is most commonly used for analysis of secondary structure.…”

“…In silks the salting-out process is accompanied by irreversible structural conversion of random coils into organized β-sheets. Based on our previous studies we propose that engineered spider silk microspheres have a core-shell structure with a shell consisting of organized β-sheets and β-turns and a core of 3 10 -helices and random coils (Neubauer et al, 2013; Rabotyagova et al, 2010). Nonorganized morphologies were observed in the case of H(AB) 2 under the same conditions, likely due to the inability of short hydrophobic domains to form stable packing arrangements.…”

“…Previously, we demonstrated the role of poly(alanine) distributions on β-sheet formation in spider silk block copolymers, using Fourier transform infrared spectroscopy (FTIR) and wide angle X-ray scattering (WAXS) to demonstrate that the number of poly(A) domains had a direct influence on the formation of crystalline β-sheets (Rabotyagova et al, 2010). In the present study, the goal was to understand the effect of peptide block length on the propensity to support self-assembly, a key step in formation of functional materials.…”

Control of silicification by genetically engineered fusion proteins: Silk–silica binding peptides

“…6). This phenomenon may be correlated to β-sheet content in the films, which form due to the hydrophobic polyalanine domains [33], perhaps shielding the silica-binding domains from the condensation reactions.…”