Structural characterization of alpha-lactalbumin nanotubes

Nanotubes are formed by self-assembly of the milk protein alpha-lactalbumin, after partial hydrolysis by a protease from Bacillus licheniformis. These unique nanotubes are formed only in the presence of an appropriate cation at neutral pH. The alpha-lactalbumin nanotube is a heterogeneous self-assembled structure comprising diverse hydrolysis products of alpha-lactalbumin with molar masses around 11 kDa. On the basis of the mass spectrometry, circular dichroism and cryo-electron microscopy results presented here, and previous atomic force microscopy and scattering results, the alpha-lactalbumin nanotube is proposed to comprise dimeric building blocks, which self-assemble into a 10-start right-handed helix via beta-sheet stacking. The self-assembled protein nanotubes presented here can serve as a model for artificial nanotubes or possibly be used in nanotechnological applications.