User:Vinícius M. Neto/Sandbox 1

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Function

Basic structure

The N-Terminal domain of the fibroin heavy chain (fibNT 3UA0) is a homo 4-mer composed of 268 residues, being most of them (hidrophilic amino acids in marron and hidrophobic in medium blue). FibNTs is a homodimer with 8 alternated β-sheets and a disordered C-terminus portion (Gly109-Ser126). Its two chains (chain A and chain B) are roughly the same but for the N-terminal segments (Phe26-Val35), that form a short helix packing in the chain A and a loop in the B.

Oligomerization

At a neutral pH, the FibNT exists in a random coil state, which prevents premature formation of β-sheets. As the pH decreases to around 6.0, FibNT undergoes a structural transition to form β-sheets. This pH drop mirrors the natural process occurring as fibroin moves from the posterior to the anterior silk gland of the silkworm.FibNT undergoes a conformational change from a random coil to β-sheets when the pH decreases to around 6.0. This transition is critical for dimerization and subsequent oligomerization.

Dynamic light scattering (DLS) and electron microscopy (EM) show that FibNT forms micelle-like oligomers as pH decreases. This suggests that FibNT acts as a pH-sensitive module, initiating self-assembly under acidic conditions similar to those in the silk gland lumen.

Relevance

Structural highlights

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