We present a straightforward， versatile method for expressing and purifying β-amyloid (Aβ40) and transmembrane peptides derived from β-amyloid precursor protein (Aβ55). In principle， these methods should be applicable to other types of strongly aggregating peptides. We start with a DNA plasmid encoding a HexaHis tag with a flexible， hydrophilic linker sequence， followed by a cleavage site， and then Aβ peptides. The HexaHis tag rather than a protein fusion partner (e.g.， GST) obviates the need for a folded protein in affinity purification. Second， we present two cleavage methods， using either Factor Xa or BNPS-Skatole. Although the latter procedure requires subsequent reduction of the produc... More
We present a straightforward， versatile method for expressing and purifying β-amyloid (Aβ40) and transmembrane peptides derived from β-amyloid precursor protein (Aβ55). In principle， these methods should be applicable to other types of strongly aggregating peptides. We start with a DNA plasmid encoding a HexaHis tag with a flexible， hydrophilic linker sequence， followed by a cleavage site， and then Aβ peptides. The HexaHis tag rather than a protein fusion partner (e.g.， GST) obviates the need for a folded protein in affinity purification. Second， we present two cleavage methods， using either Factor Xa or BNPS-Skatole. Although the latter procedure requires subsequent reduction of the product， we describe methods for minimizing side reactions. Because the use of BNPS-Skatole obviates the need for a folded protein in the cleavage reaction， it is compatible with harsh conditions (e.g.， inclusion of detergents and denaturants) needed to solubilize the fusion proteins; such conditions tend to inactivate Factor Xa. Finally， we also describe purification strategies for Aβ40 and Aβ55 using FPLC and/or reverse phase HPLC. Yields of peptide after these BNPS-Skatole cleavage and peptide reduction， though subquantitative， greatly exceed those obtained using Factor Xa cleavage， as the reaction of BNPS-Skatole is insensitive to the presence of detergents and denaturants， and therefore can be used to produce highly aggregative and low solubility peptides such as Aβ55. Trp is a low abundance amino acid in proteins generally， and for peptides like Aβ55， and other transmembane peptides lacking Trp in relevant positions， this cleavage method remains a useful option.
