Suppression of Sup35 amyloid fibril formation by group II chaperonin from Thermoplasma acidophilum

The Group II chaperonin from Thermoplasma acidophilum was added to the in vitro amyloid fibrillation reaction of yeast Sup35NM protein to assess its effects. By measuring the formation of Sup35NM fibrils in real time using the fluorescent dye Thioflavin T, we found that the addition of T. acidophilum-cpn α16, α1, and β1 proteins suppressed fibril formation. Addition of a 0.1 molar-equivalent T. acidophilum-cpn α16 relative to Sup35NM prolonged the initial lagtime of fibril formation and decreased the rate of fibril extension. Addition of 1 or 3 molar-equivalents of T. acidophilum-cpn monomers also produced a similar effect. Delayed addition of these chaperonins after the initial lag phase did not suppress fibril formation. Interestingly, these effects were also observed upon adding only the apical domain segments of α and β-subunits, and we also found that deletion of the helical protrusion in the apical domain of these segments led to an abolishment of the suppression effects. A synthetic peptide whose sequence corresponded to the helical protrusion also displayed a suppression effect, which indicated that archaeal group II chaperonin binds to Sup35NM through the helical protrusion of the apical domain. These findings suggest that group II chaperonin might be actively involved in suppressing amyloid fibril formation, in addition to acting as a protein folding assistant.