The Abundance of Phenylalanine in the DNAJB6b Linker Governs Its Role in Amyloid Suppression

The molecular chaperone DNAJB6b inhibits the disease-related self-assembly of amyloid peptides in an efficient and ATP-independent manner. The molecular basis for this action is not yet fully understood, but the low-complexity region of DNAJB6b as a stand-alone peptide displays its antiamyloid formation properties and an ability to form self-assembled structures. Here, we studied the role of phenylalanine residues within the low-complexity region of the intact chaperone to gain insight into the role of these aromatic amino acid residues in chaperone-amyloid interactions. We designed, expressed, purified, and tested eight variants with various numbers of phenylalanine residues within the low-complexity region substituted with either alanine or serine. We show that substituting only 3 of these residues significantly affects the amyloid inhibition activity of the chaperone as well as its self-assembling ability, while substituting more residues affects these functions in a dose-dependent manner. Furthermore, we show that substituting all the phenylalanine residues within the low-complexity region reduces the amyloid inhibition activity of intact DNAJB6b to the equivalent of the isolated C-terminal domain, indicating that most of the chaperone activity stems from the aromatic residues within the low-complexity region.