Physiological Impact of Intrinsic ADP Inhibition of Cyanobacterial FoF1 Conferred by the Inherent Sequence Inserted into the γ Subunit

Abstract

The F(o)F(1)-ATPase, which synthesizes ATP with a rotary motion, is highly regulated in vivo in order to function efficiently, although there remains a limited understanding of the physiological significance of this regulation. Compared with its bacterial and mitochondrial counterparts, the gamma subunit of cyanobacterial F(1), which makes up the central shaft of the motor enzyme, contains an additional inserted region. Although deletion of this region results in the acceleration of the rate of ATP hydrolysis, the functional significance of the region has not yet been determined. By analysis of rotation, we successfully determined that this region confers the ability to shift frequently into an ADP inhibition state; this is a highly conserved regulatory mechanism which prevents ATP synthase from carrying out the reverse reaction. We believe that the physiological significance of this increased likelihood of shifting into the ADP inhibition state allows the intracellular ATP levels to be maintained, which is especially critical for photosynthetic organisms.

Redox Regulation of Rotation of the Cyanobacterial F1-ATPase Containing Thiol Regulation Switch

“…These short pauses were, however, not sufficiently reliable since the bin width (ϭ 10 s) of these histograms was longer than the results obtained. Several studies have been conducted on ADP inhibition including analysis of the relevance between ADP inhibition and rotation of TF 1 ATPase (7), and an exploration of the correlation between the inserted region of the ␥ subunit and ADP inhibition of cyanobacterial F 1 (27). Though the conclusions drawn from these reports were very similar, the origin of the short pause remains to be determined.…”

“…1A), we propose that the redox switch simply takes advantage of the function of the inserted region (27) by changing conformation via a disulfide bond, though as yet there is no crystal structure for the ␥ subunit of chloroplast F 1 . As shown in this and our previous study (27), the evolutionary tuning of the ␥ subunit central region is related to ADP inhibition. However the active site on the ␣␤ surface and the expected position of the regulatory region of the ␥ subunit are located some distance apart, and no direct contact between these two regions has been reported to date.…”

“…Considering the position of the redox switch in relation to the inserted region of the ␥ subunit (Fig. 1A), we propose that the redox switch simply takes advantage of the function of the inserted region (27) by changing conformation via a disulfide bond, though as yet there is no crystal structure for the ␥ subunit of chloroplast F 1 . As shown in this and our previous study (27), the evolutionary tuning of the ␥ subunit central region is related to ADP inhibition.…”

A Conformational Change of the γ Subunit Indirectly Regulates the Activity of Cyanobacterial F1-ATPase

“…Furthermore, the mutant strain of cyanobacterium Synechocystis sp. PCC 6803, whose F 1 -␥ insertion was deleted, showed lower intracellular ATP levels due to insufficient prevention of the ATP hydrolysis activity in the dark (32,33). These results strongly suggest that the insertion plays an important role in the regulation of ATP hydrolysis activity of cyanobacterial F 0 F 1 in vivo.…”

“…In our previous studies, the mutant ␣ 3 ␤ 3 ␥ complex was prepared in which the ␥ insertion sequence of cyanobacterium Thermosynechococcus elongatus BP-1 F 1 was deleted (25,32). The mutant complex obtained showed a large increase in ATP hydrolysis activity as a consequence of the low tendency to lapse into ADP inhibition, and lower sensitivity to ⑀ inhibition.…”