The β-hairpin region of the cyanobacterial F1-ATPase γ-subunit plays a regulatory role in the enzyme activity

Abstract

The γ-subunit of cyanobacterial and chloroplast ATP synthase, the rotary shaft of F1-ATPase, equips a specific insertion region that is only observed in photosynthetic organisms. This region plays a physiologically pivotal role in enzyme regulation, such as in ADP inhibition and redox response. Recently solved crystal structures of the γ-subunit of F1-ATPase from photosynthetic organisms revealed that the insertion region forms a β-hairpin structure, which is positioned along the central stalk. The structure–function relationship of this specific region was studied by constraining the expected conformational change in this region caused by the formation of a disulfide bond between Cys residues introduced on the central stalk and this β-hairpin structure. This fixation of the β-hairpin region in the α3β3γ complex affects both ADP inhibition and the binding of the ε-subunit to the complex, indicating the critical role that the β-hairpin region plays as a regulator of the enzyme. This role must be important for the maintenance of the intracellular ATP levels in photosynthetic organisms.

Two specific domains of the γ subunit of chloroplast F o F 1 provide redox regulation of the ATP synthesis through conformational changes

“…The β-hairpin domain is positioned along the central stalk of the F 1 part, and the top of this domain appears to interact with the “DELSEED” region of the catalytic subunit F 1 -β. The DELSEED region plays a central role in torque transmission ( 28 – 30 ), and its interaction with the β-hairpin domain results in the suppression of ATP hydrolysis activity in cyanobacterial F 1 -ATPase ( 31 , 32 ). It also enables efficient ATP synthesis by cyanobacterial F 0 F 1 ( 27 ).…”

The phototroph-specific β-hairpin structure of the γ subunit of FoF1-ATP synthase is important for efficient ATP synthesis of cyanobacteria

“…These results strongly suggested that the interaction between the DELSEED loop of the β subunit and the two amino acids located at the turn of the β-hairpin structure is sufficient to induce MgADP inhibition upon ATP hydrolysis. This model was supported by our studies using recombinant α 3 β 3 γ derived from T. elongatus with nick insertion into the proximal region of the β-hairpin structure (between V 222 and T 223 ) and cross-linking experiments using disulfide bond formation between the central stalk and the β-hairpin structure within the γ subunit ( 31 , 32 ).…”

“…This was possibly explained by the interaction between the DELSEED region of the β subunit and a part of the γ subunit, although structural studies are necessary to prove this hypothesis. It was recently reported that the ε subunit of cyanobacterial F o F 1 has a different inhibitory mechanism compared with other organisms ( 41 ) and that the binding of the ε subunit caused a relative conformational change in the γ subunit ( 32 ). Consequently, the β-hairpin structure of the S. 6803 γ subunit, assisted by the ε subunit, might confer stiffness to the γ subunit and facilitate torque transmission during ATP synthesis.…”

Rotor subunits adaptations in ATP synthases from photosynthetic organisms

“…Additionally, the rotor ε -subunit that is attached to the γ -subunit and the c -ring ( Figure 1A /B) is observed in a retracted conformation that is not consistent with the ε -inhibition seen elsewhere in non-photosynthetic bacteria [ 29 , 67 , 71 - 73 ], where regulation involves the C-terminal part of the ε -subunit to reversibly interact with β -DELSEED in a so-called up-state (inhibited) or down-state (active) conformation [ 67 , 73 , 74 ]. In cyanobacteria though, the ε -subunit may be responsible for inducing the required conformational change in the γ -subunit to inhibit rotation in the ATP hydrolysis direction [ 72 , 75 ]. Structural studies of the cyanobacterial ATP synthase will help to identify which regulatory mechanisms play the most significant roles in cyanobacteria.…”