Negatively charged phospholipid membranes induce amyloid formation of medin via an alpha-helical intermediate.
Medin, a recently discovered 5.5 kDa peptide, is associated with amyloid deposits in the medial layer of human arteries and the prevalence is nearly 100% within individuals above 50 years. Presently, not much is known about its biochemical and biophysical properties or its pathway from soluble peptide to insoluble amyloid. Here we have characterized the behavior of medin in the presence of lipid membranes, using circular dichroism, isothermal titration calorimetry, differential scanning calorimetry, size exclusion chromatography, and atomic force microscopy (AFM). Medin was shown to exist as a monomer in solution with a predominantly random-coil structure. It binds lipid vesicles that have either a neutral or a negative surface potential. Upon association to membranes containing acidic lipids, it undergoes an electrostatically driven conformational change towards a mainly alpha-helical state. Prolonged incubation converts medin from an alpha-helical structure into an amyloid beta-sheet fibrillar state as confirmed by AFM. Based on these findings, we propose a mechanism of medin-amyloid formation where medin electrostatically associates in its monomeric form to biological interfaces displaying a negative potential. This process both increases the local peptide concentration and induces an aggregation-prone alpha-helical fold.
Olofsson
Anders
A
Umeå Centre for Molecular Pathogenesis, Umeå University, 901 87, Umeå, Sweden.
Borowik
Tomasz
T
Gröbner
Gerhard
G
Sauer-Eriksson
A Elisabeth
AE
D000954:Antigens, Surface / Q000737:chemistry* / Q000378:metabolism*; D002152:Calorimetry, Differential Scanning; D002850:Chromatography, Gel; D002942:Circular Dichroism; D006801:Humans; D008051:Lipid Bilayers / Q000737:chemistry*; D018625:Microscopy, Atomic Force; D008894:Milk Proteins / Q000737:chemistry* / Q000378:metabolism*; D008961:Models, Structural; D010743:Phospholipids / Q000737:chemistry*; D011487:Protein Conformation
D000954:Antigens, Surface; D008051:Lipid Bilayers; C098942:MFGE8 protein, human; D008894:Milk Proteins; D010743:Phospholipids