Differences in the Elastomeric Behavior of Polyglycine-Rich Regions of Spidroin 1 and 2 Proteins

Abstract

Two different polyglycine-rich fragments were selected as representatives of major ampullate gland spidroins (MaSp) 1 and 2 types, and their behavior in a water-saturated environment was simulated within the framework of molecular dynamics (MD). The selected fragments are found in the sequences of the proteins MaSp1a and MaSp2.2a of Argiope aurantia with respective lengths of 36 amino acids (MaSp1a) and 50 amino acids (MaSp2.2s). The simulation took the fully extended β-pleated conformation as reference, and MD was used to determine the equilibrium configuration in the absence of external forces. Subsequently, MD were employed to calculate the variation in the distance between the ends of the fragments when subjected to an increasing force. Both fragments show an elastomeric behavior that can be modeled as a freely jointed chain with links of comparable length, and a larger number of links in the spidroin 2 fragment. It is found, however, that the maximum recovery force recorded from the spidroin 2 peptide (Fmax ≈ 400 pN) is found to be significantly larger than that of the spidroin 1 (Fmax ≈ 250 pN). The increase in the recovery force of the spidroin 2 polyglycine-rich fragment may be correlated with the larger values observed in the strain at breaking of major ampullate silk fibers spun by Araneoidea species, which contain spidroin 2 proteins, compared to the material produced by spider species that lack these spidroins (RTA-clade).

Variation in the Elastic Modulus and Increased Energy Dissipation Induced by Cyclic Straining of Argiope bruennichi Major Ampullate Gland Silk

“…The concept of hidden length implies that segments of the protein chains, originally in the amorphous phase, become progressively unfolded during stretching, but until a significant unfolding occurs, those segments do not play any relevant role in the mechanical performance of silk. In this regard, studies based on the Molecular Dynamics of the polyglycine fragments characteristic of the amorphous phase show that these fragments display an elastomeric behaviour [ 36 ], independently from the detailed conformation of the participating amino acids. Beyond a given value of true strain (or, correspondingly, of true stress) at which the unfolding of a fraction of those segments initially included in the hidden length takes place, the properties of the material are essentially determined by the behavior of this fraction of the chains.…”

In-SilicoAnalyses of Molecular Force Sensors for Mechanical Characterization of Biological Systems

“…To expand and improve the applications of spider silk peptides and synthetic derivatives it is critical to understand and probe their mechanical properties and how these depend on molecular parameters and loading rates. To date, a few studies have tested the effects of design parameters like length and composition of peptide-based sensor linkers computationally or experimentally (28)(29)(30)(31). Some of these studies have revealed the mechanical effects of flow dependent stretching of spider silk, the influence of polyglycine regions and external forces on the elasticity of spider silk peptides, and details of fiber assembly.…”