Fibroin

In the fibroin β-sheet there are specific residues that are preserved in the N-terminal domain in order to prevent premature sheet formation at a neutral pH. Glu98 and Asp100 are both acidic, meaning they have negative charges when at a neutral pH. Since they have the same charge, the residues will create electrostatic repulsion which can cause the side chains to repel each other. At a low pH however, these residues would become protonated and lose their charge. When the charge repulsion is not present, hydrogen bonding and hydrophobic interactions become the main driving force of β-sheet formation. Therefore, when at a neutral pH Glu98 and Asp100 are deprotonated, and the electrostatic repulsion occurs. This repulsion reduces structural stability or can even prevent premature formation of the β-sheet. This is just one example of this interaction. This repulsion occurs between various other amino acids that the β-sheet is composed of. By preventing the premature formation, the electrostatic repulsions help ensure that the β-sheet is formed correctly which will allow for fibroin to function properly. The regulation of the β-sheet formation is especially important to the integrity of silk since fibroin is one of the primary structural proteins in silk. == Materials science ==

Although silk fibroin has been used for millennia in the textile industry, over the last 20 years, it has become very popular in materials science. This popularity stems from the discovery that silk fibroin (particularly from Bombyx mori) can be redissolved in chaotropic salt solutions such as calcium chloride or lithium bromide. This process yields an aqueous solution similar to the form found in the silkworm's gland, which can then be used to create various types of materials. Microscopic analysis characterizes silk fibroin filaments by a triangular prism cross-section, which enhances optical luster through refraction, and a smooth longitudinal surface, which minimizes the coefficient of friction compared to other natural fibers. == Degradation ==

Many species of Amycolatopsis and Saccharotrix bacteria are able to degrade both silk fibroin and polylactic acid. == References ==