Honeybee silk is released from secretory cells and polymerises as birefringent tactoids in the lumen
while silk is spun by a spinneret at the tip of the labium–hypopharynx and contains ά-helical proteins arranged
in a four-strand coiled-coil structure. Wet fibres are only half as stiff as dried ones, but are equal in strength.
The fibroin is hygroscopic and lithium thiocyanate and urea eliminate the yield point tested on both dry and wet
fibres. The slopes of the solvent-related curves are reduced compared to those tested in water. Silk sheets are
independent of temperature when deformed in tension. This fibre is rather crystalline and its hydration
sensitivity, expressed as the ratio of the elastic modulus of wet to that of dry fibre, is 0.53. The ά-helical
fibroins are predicted to have an antiparallel tetrameric configuration that is shown as a possible structural
model. The molecular structure of ά-helical proteins maximizes their robustness with minimal use of building
materials. In conclusion, it appears that the composition, molecular topology and amino acid content and
sequence are a highly conserved feature in the evolution of silk in Apis species.