Guanidinium chloride

Ultrapure urea and guanidinium chloride were purchased from MP Biomedicals (CA, USA). All other reagents were purchased from Sigma Chemical Co. (MO, USA) or ThermoFisher (MA, USA). The C-amidated, N-acetylated AWPAK peptide was synthesised by ChinaPeptides (Shanghai, China). SOD1 H43Y noloops and Escherichia coli cytochrome b₅₆₂ F65W proteins were donated by Mikael Oliveberg (University of Stockholm) and Paul Barker (Cambridge University), respectively. α-Spectrin expression vectors were gifts from Jane Clarke (Cambridge University). LQRRRETQV and LQRRRETQ-Abu peptides and the PDZ1 expression vector were gifts from Per Jemth (Uppsala University). Barley chymotrypsin inhibitor-2 (CI2), murine FBP28 WW domain, hepatitis B core protein, the PDZ1 of the post-synaptic density protein 95 (PSD-95) with the F95W mutation (PDZ1 F95W) and α-spectrin constructs were expressed and purified as reported [10,16,33,34] . Protein concentrations were determined spectrophotometrically from calculated molar extinction coefficients.