Interaction of phage chaperonin OBP domains with amyloidogenic proteins

GroEL-like chaperonins encoded by bacterial viruses have unique features compared to other group I and II chaperonins. Here, the properties of the single-ring chaperonin of the bacteriophage OBP Pseudomonas fluorescens were further studied. To understand the role of the chaperonin domains in its function, two deletion variants of the chaperonin OBP were obtained. One represented the isolated apical domain (AD) only and the other was a chaperonin without apical domains (OBPΔAD). It was shown that removal of the apical domains slightly destabilises the chaperonin structure, but does not affect its heptameric assembly. In addition, the chaperonin without the apical domains retains its ATPase activity and exhibits the properties that are characteristic of the full-length chaperonin OBP. In the presence of ATP, the mutant chaperonin OBPΔAD protects the phage endolysin from thermal aggregation and promotes the fibrillation of two amyloidogenic proteins, α-synuclein and the prion protein. In the absence of ATP, OBPΔAD is able to bind α-synuclein monomers in the same way as the full-length chaperonin OBP, thus preventing their spontaneous fibrillation. The recombinant chaperonin apical domain, lacking ATPase activity, binds α-synuclein monomers independently of ATP presence, preventing amyloid formation. The results obtained suggest that, in mutant OBP, which lacks apical domains, substrate proteins, including non-specific ones, are capable of binding to the internal cavity formed by the other two chaperonin domains. The possible role of chaperonin domains in regulating the pathological transformation of amyloidogenic proteins is discussed.