Self-assembly and adhesive properties of Pollicipes pollicipes barnacle cement protein cp19k: influence of pH and ionic strength

Marine organisms such as barnacles rely on a complex underwater adhesive system, driven by self-assembly and intermolecular associationsbetween cement proteins, for permanent attachment to a variety of surface types. In this study, we investigated the influenceof environmental parameters on the self-assembly of recombinant cp19k, a key adhesive protein in Pollicipes pollicipes. UsingTEM imaging, a low pH (4.0) and high salt concentration (600 mM NaCl) environment, mimicking P. pollicipes gland conditions, was identified to promote the formation of extended, needle-like fibrils by the cp19k protein. The ?-amyloid nature of fibrilsformed under these conditions and at high pH/low salt concentration was confirmed by Thioflavin T assay. Non-fibrillar cp19kadhered most effectively to hydrophilic and hydrophobic surfaces under low pH/low salt concentration conditions, while preformedfibrils retained their adhesion ability upon switching to a high pH/high salt concentration environment, which was designedto mimic the change in the protein environment upon secretion in vivo. These findings support the hypothesis that fibril formationoccurs in the acidic, iso-osmotic gland of the barnacle, with delayed cement curing enabling fibril secretion for sustained adhesionof the organism. The study provides insight into the environmental sensitivity of cp19k structure-function dynamics and maysupport the design of bioinspired adhesives and biomaterials.