Aciniform Spider Silk Proteins: Investigating Solution-State Assembly and the Potential of Silk Nanoparticles as a Drug Delivery Vehicle

Abstract

Spider and silkworm silks form a wide variety of biomaterials with desirable mechanical properties and biocompatibility. The process of fibrillogenesis from silk solution is not fully understood, but may be dependent on micellar assemblies formed in the gland. In this study the micelle formation and surface adsorption of a recombinant aciniform repeat unit (W1) were investigated, as this may give clues to the fibrillogenic pathway. It was found that micelle-like assemblies formed by W1 are very low in yield, however the protein self-assembles at the liquid-air interface. Aciniform proteins with multiple repeats showed visco-elastic properties at the surface layer while W1 did not. The alignment and conformational changes of aciniform proteins at the liquid-air interface may be relatable to those which occur during fibrillogenesis. Disruption to helix 5 of the W1 protein may be involved in early conformational transitions during the process of fibrillogenesis. The R36W residue of a W1 variant, which is on the protein surface beneath helix-5, was found to make the variant less stable than the wild-type. This may be due to disruption to helix 5 caused by the substitution, which may expose a hydrophobic surface that encourages interprotein interactions. Silkworm and dragline spider silk are well established as potential drug delivery vehicles, however aciniform silks have not yet been investigated for that purpose. Nanoparticles of W1 were formed by a desolvation process and characterised in terms of size and conformation, yielding a novel biomaterial for aciniform silk. Aciniform nanoparticles may have different drug-compatibilities and desirable uptake and release properties compared to other silk nanoparticles, though this remains to be investigated.