¹To whom correspondence should be addressed. Phone: +81-6-6879-8615, Fax: +81-6-6879-8616, E-mail: yutani@protein.osaka-u.ac.jp

Abbreviations: PfPCP, TlPCP, and BaPCP are pyrrolidone carboxyl peptidase from Pyrococcus furiosus, Thermococcus litoralis, and Bacillus amyloliquefaciens, respectively; PfC142/188S, Cys-free mutant PfPCP (Cys142—>Ser and Cys188—>Ser); DSC, differential scanning calorimetry; NCS, non-crystallographic symmetry; SPMP, stability profiles of mutant proteins.