Interfacial Aβ fibril formation is modulated by the disorder-order state of the lipids: The concept of the physical environment as amyloid inductor in biomembranes

The behavior of amphiphilic molecules such as lipids, peptides and their mixtures at the air/water interface allow us to evaluate and visualize the arrangement formed in a confined and controlled surface area. We have studied the surface properties of the zwitterionic DPPC lipid and A beta(1-40) amyloid peptide in mixed films at different temperatures (from 15 to 40(degrees)C). In this range of temperature the surface properties of pure A beta(1-40) peptide remained unchanged, whereas DPPC undergoes its characteristic liquid-expanded -> liquid-condensed bidimensional phase transition that depends on the temperature and lateral pressure. This particular property of DPPC makes it possible to dynamically study the influence of the lipid phase state on amyloid structure formation at the interface in a continuous, isothermal and abrupt change on the environmental condition. As the mixed film is compressed the fibril-like structure of A beta(1-40) is triggered specifically in the liquid-expanded region, independently of temperature, and it is selectively excluded from the well-visible liquid condensed domains of DPPC. The A beta amyloid fibers were visualized by using BAM and AFM and they were Thio T positive. In mixed DPPC/A beta (1-40) films the condensed domains (in between 11 mN/m to 20 mN/m) become irregular probably due to the fibril-like structures is imposing additional lateral stress sequestering lipid molecules in the surrounding liquidexpanded phase to self-organize into amyloids.