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

Abstract

The ␥ and ⑀ subunits of F 0 F 1 -ATP synthase from photosynthetic organisms display unique properties not found in other organisms. Although the ␥ 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 ⑀ subunit strongly inhibits ATP hydrolysis activity. To understand the physiological significance of these phenomena, we studied mutant strains with (i) a C-terminally truncated ⑀ (⑀ ⌬C ), (ii) ␥ lacking the inserted sequence (␥ ⌬198 -222 ), and (iii) a double mutation of (i) and (ii) in Synechocystis sp. PCC 6803. Although thylakoid membranes from the ⑀ ⌬C 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 ⑀ ⌬C and ␥ ⌬198 -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.

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.…”

Functional Characterization of the Small Regulatory Subunit PetP from the Cytochrome b6f Complex in Thermosynechococcus elongatus

“…For data interpretation, linear and cyclic electron transport routes for PQ reduction and cytochrome c oxidation by PSI and cytochrome c oxidase have been considered (Yu et al, 1993;Yeremenko et al, 2005). The following set of equations describes the inhibitor experiments ( Figure 6A): Light saturation curves of the photosynthetic electron transport rate were recorded at defined light intensities using a Dual PAM-100 system (Walz) according to Xu et al (2008) and Imashimizu et al (2011) with stepwise increase of the actinic light intensity from 0 to 830 mE m 22 s 21 with 30-s adaptation periods. Maximal fluorescence yields were obtained by saturating light pulses (duration 60 s, intensity 10,000 mE m 22 s 21 ) at the end of each 30-s period.…”

1 Cyanobacterial design cell for the production of hydrogen from water

“…lower proton gradient and less acidic pH i . Although the design of an artificial channel across the thylakoid membrane -possibly under the control of the hydrogenase promoter -has been suggested [22], this could be realized more easily in a ε Δc -ATPase mutant, which indeed shows approximately a doubling of the (linear) electron transport in comparison with WT ( Figure 1.4) [1]. This partial uncoupling should result in a reduced production of ATP, which in turn may cause deficits in growth due to metabolic problems.…”

“…Both groups have still preserved some routes for light dependent H 2 production which are illustrated in Figure 1. 1 Cyanobacteria contain exclusively [NiFe]-type H 2 ases which are coupled to photosynthetic electron transport via NADPH [13], which in turn is produced by Ferredoxin-NADP + -Oxidoreductase (FNR), or may even be coupled directly to Ferredoxin (Fd) [14] (for details see Chapter 10). Between Photosystem 1 (PS1) and this H 2 ase several electron transfer steps are involved including many competitive reactionsespecially involving Ferredoxin (Fd) and NADPH -which "dilute" the amount of electrons finally available for hydrogen production.…”