Rotary properties of hybrid F₁-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 FoF1-ATP synthase. Despite the highly conserved amino acid sequence of the catalytic core subunits: alpha and beta, 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)1s: thermophilic Bacillus PS3 (TF1), bovine mitochondria (bMF(1)), and Paracoccus denitrificans (PdF1), 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 0 and the couplings between alpha-beta. 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.