Molecular dynamics simulations of the minor ampullate spidroin modular amino acid sequence from Parawixia bistriatra: insights into silk tertiary structure and fibre formation.

Spider fibres are primarily composed of proteins that are secreted by specialised glands found in different groups of arthropods. Because of their unique mechanical characteristics, it is of great interest to understand how the influence of repetitive modules within the fibres affects the final protein structure. Because each fibre is composed of a diverse set of repeated modular sequences, the differences between fibres allow for their structural comparison and, thereby, their functional comparison. Herein, we present molecular dynamics simulations of partial sequences from minor ampullate Spidroin (MiSp) silk of the Brazilian species Parawixia bistriata. Our data show that the formation of β-sheet structures is directly related to the N-termini alignment of the modules. The N-terminal alignment gives rise to a high number of hydrogen bonds whose formation is driven by repeated alanine (Ala) sequences, which, in turn, lead to increased fibre strength. This increased fibre strength contributes significantly to the final tertiary structure of the silk.