Rotary properties of hybrid F(1)-ATPases consisting of subunits from different species

F(1)-ATPase (F(1)) is an ATP-driven rotary motor protein ubiquitously found in many species as the catalytic portion of F(o)F(1)-ATP synthase. Despite the highly conserved amino acid sequence of the catalytic core subunits: α and β, F(1) shows diversity in the maximum catalytic turnover rate V(max) and the number of rotary steps per turn. To study the design principle of F(1), we prepared eight hybrid F(1)s composed of subunits from two of three genuine F(1)s: thermophilic Bacillus PS3 (TF(1)), bovine mitochondria (bMF(1)), and Paracoccus denitrificans (PdF(1)), differing in the V(max) and the number of rotary steps. The V(max) of the hybrids can be well fitted by a quadratic model highlighting the dominant roles of β and the couplings between α-β. Although there exist no simple rules on which subunit dominantly determines the number of steps, our findings show that the stepping behavior is characterized by the combination of all subunits.