Epitaxial assembly dynamics of mutant amyloid β25–35_N27C fibrils explored with time-resolved scanning force microscopy

Self-assembling Bioadhesive Inspired by the Fourth Repetitive Sequence of Balanus albicostatus Cement Protein 20 kDa (Balcp-20 k)

Barnacle cement proteins are multi-protein complexes composed of a series of functionally related synergistic proteins that enable barnacles to adhere strongly and consistently to various underwater substrates. There is no post-translational modification of barnacle cement proteins, which provides a possibility for the synthesis of similar adhesive materials. Balcp-20 k has four repetitive sequences with multiple conserved cysteine groups. Whether these repeats are separate functional units and the role of cysteine in adhesion is not clear. In order to investigate the adhesion properties of Balcp-20 k, we amplified and expressed R4 (DHLACNAKHPCWHKHCDCFC)₄, which is a quadruple repeat of Balcp-20 k's fourth repetitive sequence, and S0R4 (DHLASNAKHPSWHKHSDSFS)₄, all cysteine of R4 replaced by serine. Analysis showed that R4 had a similar structure to Balcp-20 k, and the amyloid fibrils structure formed by self-assembly of R4 played an important role in improving the adhesion strength. The absence of disulfide bonds in S0R4 prevents self-assembly, and the failure of self-assembly after the reduction of disulfide bonds of R4 by DTT indicates that disulfide bonds play an important role in self-assembly. With adhesion and coating analysis, it was found that R4 has good adhesion on different materials surfaces, which is better than Balcp-20 k, while S0R4 has weak adhesion, which is only better than BSA.

Surface effects mediate self-assembly of amyloid-β peptides

Here we present a label-free method for studying the mechanism of surface effects on amyloid aggregation. In this method, spin-coating is used to rapidly dry samples, in a homogeneous manner, after various incubation times. This technique allows the control of important parameters for self-assembly, such as the surface concentration. Atomic force microscopy is then used to obtain high-resolution images of the morphology. While imaging under dry conditions, we show that the morphologies of self-assembled aggregates of a model amyloid-β peptide, Aβ(12-28), are strongly influenced by the local surface concentration. On mica surfaces, where the peptides can freely diffuse, homogeneous, self-assembled protofibrils formed spontaneously and grew longer with longer subsequent incubation. The surface fibrillization rate was much faster than the rates of fibril formation observed in solution, with initiation occurring at much lower concentrations. These data suggest an alternative pathway for amyloid formation on surfaces where the nucleation stage is either bypassed entirely or too fast to measure. This simple preparation procedure for high-resolution atomic force microscopy imaging of amyloid oligomers and protofibrils should be applicable to any amyloidogenic protein species.