Prefoldin is a molecular chaperone that captures a protein-folding intermediate and transfers it to a group 11 chaperonin for correct folding. Previous studies of archaeal prefoldins have shown that prefoldin only possesses holdase activity and is unable to fold unfolded proteins by itself In this study, we have demonstrated for the first time that a prefoldin from hyperthermophilic archaeon, Pyrococcus horikoshu OT3 (PhPFD). exhibits refolding activity for denatured lysozyme at temperatures relatively lower than physiologically active temperatures. The interaction between PhPFD and denatured lysozyme was investigated by use of a surface plasmon resonance sensor at various temperatures Although PhPFD showed strong affinity for denatured lysozyme at high temperature, it exhibited relatively weak interactions at lower temperature. The protein-folding seems to occur through binding and release from PhPFD by virtue of the weak affinity Out results also imply that prefoldin might be able to contribute to the folding of some cellular proteins whose affinity with prefoldin is weak. (C) 2009 Elsevier Inc All rights reserved.