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ClpB, a member of the expanded superfamily of ATPases associated with diverse cellular activities (AAA+), forms a ring-shaped hexamer and coop-erates with the DnaK chaperone system to reactivate aggregated proteins in an ATP-dependent manner. | IFEBS Journal Roles of conserved arginines in ATP-binding domains of AAA chaperone ClpB from Thermus thermophilus Takashi Yamasaki1 Yosuke Nakazaki1 Masasuke Yoshida2 and Yo-hei Watanabe1 1 Department of Biology Faculty of Science and Engineering Konan University Okamoto Kobe Japan 2 Department of Molecular Biosciences Kyoto Sangyo University Motoyama-Kamigamo Japan Keywords AAA aggregation arginine finger chaperone ClpB Correspondence Y-h. Watanabe Department of Biology Faculty of Science and Engineering Konan University Okamoto 8-9-1 Kobe 658-8501 Japan Fax Tel 81 78 435 2514 E-mail ywatanab@center.konan-u.ac.jp Received 7 March 2011 revised 30 April 2011 accepted 6 May 2011 doi 10.1111 j.1742-4658.2011.08167.x ClpB a member of the expanded superfamily of ATPases associated with diverse cellular activities AAA forms a ring-shaped hexamer and cooperates with the DnaK chaperone system to reactivate aggregated proteins in an ATP-dependent manner. The ClpB protomer consists of an N-termi-nal domain an AAA module AAA-1 a middle domain and a second AAA module AAA-2 . Each AAA module contains highly conserved WalkerA and WalkerB motifs and two arginines AAA-1 or one arginine AAA-2 . Here we investigated the roles of these arginines Arg322 Arg323 and Arg747 of ClpB from Thermus thermophilus in the ATPase cycle and chaperone function by alanine substitution. These mutations did not affect nucleotide binding but did inhibit the hydrolysis of the bound ATP and slow the threading of the denatured protein through the central pore of the T. thermophilus ClpB ring which severely impaired the chaperone functions. Previously it was demonstrated that ATP binding to the AAA-1 module induced motion of the middle domain and stabilized the ClpB hexamer. However the arginine mutations of the AAA-1 module destabilized the ClpB hexamer even though ATP-induced motion of the middle domain was not affected. These results indicated that the three arginines are crucial for ATP hydrolysis and