Production, structure and in vitro degradation of electrospun honeybee silk nanofibers

Honeybees produce silken cocoons containing four related fibrous proteins. High levels of each of the honeybee silk proteins can be produced recombinantly by fermentation in Escherichia coli. In this study we have used electrospinning to fabricate a single recombinant honeybee silk protein, AmelF3, into nanofibers of around 200 nm diameter. Infrared spectroscopy found that the molecular structure of the nanofibers was predominantly coiled coil, essentially the same as native honeybee silk. Mats of the honeybee nanofibers were treated with methanol or by water annealing, which increased their β-sheet content and rendered them water insensitive. The insoluble mats were degraded by protease on a time scale of hours to days. The protease gradually released proteins from the solid state and these were subsequently rapidly degraded into small peptides without the accumulation of partial degradation products. Cell culture assays demonstrated that the mats allowed survival, attachment and proliferation of fibroblasts. These results indicate that honeybee silk proteins meet many prerequisites for use as a biomaterial.