Regulation of F0F1-ATPase from Synechocystis sp. PCC 6803 by γ and ∈ Subunits Is Significant for Light/Dark Adaptation

Mari Imashimizu,Gábor Bernát,Ei-Ichiro Sunamura,Martin Broekmans,Hiroki Konno,Kota Isato,Matthias Rögner,Toru Hisabori

doi:10.1074/jbc.m111.234138

Mari Imashimizu, Gábor Bernát + Show 6 more

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https://doi.org/10.1074/jbc.m111.234138

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Abstract

The γ and ε subunits of F(0)F(1)-ATP synthase from photosynthetic organisms display unique properties not found in other organisms. Although the γ subunit of both chloroplast and cyanobacterial F(0)F(1) contains an extra amino acid segment whose deletion results in a high ATP hydrolysis activity (Sunamura, E., Konno, H., Imashimizu-Kobayashi, M., Sugano, Y., and Hisabori, T. (2010) Plant Cell Physiol. 51, 855-865), its ε subunit strongly inhibits ATP hydrolysis activity. To understand the physiological significance of these phenomena, we studied mutant strains with (i) a C-terminally truncated ε (ε(ΔC)), (ii) γ lacking the inserted sequence (γ(Δ198-222)), and (iii) a double mutation of (i) and (ii) in Synechocystis sp. PCC 6803. Although thylakoid membranes from the ε(ΔC) strain showed higher ATP hydrolysis and lower ATP synthesis activities than those of the wild type, no significant difference was observed in growth rate and in intracellular ATP level both under light conditions and during light-dark cycles. However, both the ε(ΔC) and γ(Δ198-222) and the double mutant strains showed a lower intracellular ATP level and lower cell viability under prolonged dark incubation compared with the wild type. These data suggest that internal inhibition of ATP hydrolysis activity is very important for cyanobacteria that are exposed to prolonged dark adaptation and, in general, for the survival of photosynthetic organisms in an ever-changing environment.

Highlights

The extrinsic, catalytic F1 moiety is responsible for ATP synthesis and hydrolysis and has a subunit composition of ␣3␤3␥␦⑀, with the catalytic sites predominantly located on the ␤ subunits [4]
As the amino acid sequence of the ⑀ subunit is well conserved among bacteria, the optimal position for the stop codon could be determined by using the crystal structure of the ⑀ subunit of F1 from the thermophilic Bacillus PS3 (TF1) [34]
In ATPase from Escherichia coli and Bacillus PS3, the ⑀ subunit is a prerequisite for binding F1 to F0, F1 from E. coli with a C-terminally truncated ⑀ subunit is still able to bind to F0 (36 –39)

Summary

To whom correspondence should be addressed

F0F1-ATP synthase remained highly conserved during evolution. The enzyme consists of two structurally and functionally distinct elements: F0 and F1 [1,2,3]. The most plausible explanation for which photosynthetic organisms have developed a down-regulation system for ATPase activity by ␥ and ⑀ subunits is to prevent wasteful ATP hydrolysis, this providing a stable intracellular ATP level in darkness PCC 6803 (hereafter referred to as Synechocystis2), which lacks this inserted region (␥⌬198–222) [21] Detailed analysis of this strain and single molecule experiments of the ␣3␤3␥ complex containing the same mutation within the ␥ subunit of Thermosynechoccus elongatus BP-1, indicated that the evolutionary insertion of an additional segment into the ␥ subunit enables the frequent lapse of the enzyme into an ADPinhibition state [21]; this apparently helps to maintain the cellular ATP level in the dark. Our results are discussed in the context of cellular strategies to overcome environmental stress conditions such as long term darkness or very low light

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