Self-assembly of peptide-amphiphile C12-Abeta(11-17) into nanofibrils.

A peptide-amphiphile (C12-Abeta(11-17)) was constructed with a key fragment of amyloid beta-peptide (Abeta(11-17)) attached to dodecanoic acid through an amide bond. The self-assembly behavior of C12-Abeta(11-17) in aqueous solution is studied at 25 degrees C and at pH 3.0 and 10.0. Abeta(11-17) cannot form ordered self-assemblies. But C12-Abeta(11-17) exhibits a very strong ability to form ordered nanofibrils, and the specific fine structure of the nanofibrils can be modulated simply by adjusting the concentration or pH. The critical micelle concentration of C12-Abeta(11-17) was determined as 0.063 and 0.11 mM at pH 3.0 and 10.0, respectively, indicating a stronger assembling ability of C12-Abeta(11-17) at acidic pH. In 0.47 mM C12-Abeta(11-17) solution at pH 3.0, rodlike fibrils with a diameter of approximately 5 nm and varying length of hundreds of nanometers are observed. When the C12-Abeta(11-17) concentration increases to 1.87 mM at pH 3.0, the above rodlike fibrils pack in parallel and form tapelike fibrils through lateral association. In 1.87 mM C12-Abeta(11-17) solution at pH 10.0, twisted fibrils with regular periodicity of approximately 200 nm are formed by the twisting of approximately 20 nm wide and approximately 11 nm thick nanoribbons. The hydrophobic moiety is necessary in fibril formation, whereas the beta-sheet secondary structure of the peptide moiety plays an essential role in the twisting morphology. This work helps to understand the possible mechanism in amyloid fibrillogenesis and provides an approach to inscribe biological signals in self-assemblies with potential application in biomaterial fabrication.