Redox regulation of CF1-ATPase involves interplay between the γ-subunit neck region and the turn region of the ßDELSEED-loop.

ABSTRACT

The soluble F1 complex of ATP synthase (FoF1) is capable of ATP hydrolysis, accomplished by the minimum catalytic core subunits α3ß3γ. A special feature of cyanobacterial F1 and chloroplast F1 (CF1) is an amino acid sequence inserted in the γ-subunit. The insertion is extended slightly into the CF1 enzyme containing two additional cysteines for regulation of ATPase activity via thiol modulation. This molecular switch was transferred to a chimeric F1 by inserting the cysteine-containing fragment from spinach CF1 into a cyanobacterial γ-subunit [Y. Kim et al., redox regulation of rotation of the cyanobacterial F1-ATPase containing thiol regulation switch, J Biol Chem, 286 (2011) 9071-9078]. Under oxidizing conditions, the obtained F1 tends to lapse into an ADP-inhibited state, a common regulation mechanism to prevent wasteful ATP hydrolysis under unfavorable circumstances. However, the information flow between thiol modulation sites on the γ-subunit and catalytic sites on the ß-subunits remains unclear. Here, we clarified a possible interplay for the CF1-ATPase redox regulation between structural elements of the ßDELSEED-loop and the γ-subunit neck region, i.e., the most convex part of the α-helical γ-termini. Critical residues were assigned on the ß-subunit, which received the conformation change signal produced by disulfide/dithiol formation on the γ-subunit. Mutant response to the ATPase redox regulation ranged from lost to hypersensitive. Furthermore, mutant cross-link experiments and inversion of redox regulation indicated that the γ-redox state might modulate the subunit interface via reorientation of the ßDELSEED motif region.