α‑Helix-Mediated Protein Adhesion

Proteins have been adopted by natural living organisms
to create
robust bioadhesive materials, such as biofilms and amyloid plaques
formed in microbes and barnacles. In these cases, β-sheet stacking
is recognized as a key feature that is closely related to the interfacial
adhesion of proteins. Herein, we challenge this well-known recognition
by proposing an α-helix-mediated interfacial adhesion model
for proteins. By using bovine serum albumin (BSA) as a model protein,
it was discovered that the reduction of disulfide bonds in BSA results
in random coils from unfolded BSA dragging α-helices to gather
at the solid/liquid interface (SLI). The hydrophobic residues in the
α-helix then expose and break through the hydration layer of
the SLI, followed by the random deposition of hydrophilic and hydrophobic
residues to achieve interfacial adhesion. As a result, the first assembled
layer is enriched in the α-helix secondary structure, which
is then strengthened by intermolecular disulfide bonds and further
initiates stepwise layering protein assembly. In this process, β-sheet
stacking is transformed from the α-helix in a gradually evolving
manner. This finding thus indicates a valuable clue that β-sheet-featuring
amyloid may form after the interfacial adhesion of proteins. Furthermore,
the finding of the α-helix-mediated interfacial adhesion model
of proteins affords a unique strategy to prepare protein nanofilms
with a well-defined layer number, presenting robust and modulable
adhesion on various substrates and exhibiting good resistance to acid,
alkali, organic solvent, ultrasonic, and adhesive tape peeling.