Low pH Modulates the Macroorganization and Thermal Stability of PSII Supercomplexes in Grana Membranes

Abstract

Protonation of the lumen-exposed residues of some photosynthetic complexes in the grana membranes occurs under conditions of high light intensity and triggers a major photoprotection mechanism known as energy dependent nonphotochemical quenching. We have studied the role of protonation in the structural reorganization and thermal stability of isolated grana membranes. The macroorganization of granal membrane fragments in protonated and partly deprotonated state has been mapped by means of atomic force microscopy. The protonation of the photosynthetic complexes has been found to induce large-scale structural remodeling of grana membranes-formation of extensive domains of the major light-harvesting complex of photosystem II and clustering of trimmed photosystem II supercomplexes, thinning of the membrane, and reduction of its size. These events are accompanied by pronounced thermal destabilization of the photosynthetic complexes, as evidenced by circular dichroism spectroscopy and differential scanning calorimetry. Our data reveal a detailed nanoscopic picture of the initial steps of nonphotochemical quenching.

The Use of Contact Mode Atomic Force Microscopy in Aqueous Medium for Structural Analysis of Spinach Photosynthetic Complexes

“…The PSII-OEC particles in these preparations exhibited a semicrystalline arrangement. Moderately high-resolution CM-AFM images of pea (Pisum sativum) grana membranes isolated using the Berthold-Babcock-Yocum procedure (Triton X-100 detergent; Berthold et al, 1981;Stoichev et al, 2015), with samples incubated at room temperature for 0.5 to 1 h prior to imaging, exhibited a disordered PSII-OEC particle arrangement, as was observed in our work. A disordered PSII-OEC arrangement was also observed in grana isolated from a-DM-solubilized membranes (Johnson et al, 2014).…”

“…The similarity of our height measurements with those of Johnson et al (2014), which are slightly more than those of Stoichev et al (2015), suggests that the tip force that we applied was unlikely to create compression. The height variations observed among the studies might exist in vivo, as suggested by Kou ril et al (2011).…”

“…The PSII-OEC peak height that we determined is slightly less than that of Sznee et al (2011;4.5-5 nm), comparable to that of Johnson et al (2014; 4 6 0.1 nm), and slightly higher than that of Stoichev et al (2015; 2.97 6 0.34 nm). The similarity of our height measurements with those of Johnson et al (2014), which are slightly more than those of Stoichev et al (2015), suggests that the tip force that we applied was unlikely to create compression.…”

Atomic Force Microscopy Visualizes Mobility of Photosynthetic Proteins in Grana Thylakoid Membranes

“…Atomic force microscopy (AFM) is a unique technique that enables direct observation of macromolecules at high spatial resolution ( x , y < 1 nm and z < 0.1 nm) in aqueous conditions. AFM has been used to characterize the structure and organization of thylakoid membranes ( 19 , 20 , 21 , 22 , 23 , 24 ). These studies support and complement EM reports about how PSII and LHCII organization is affected by illumination ( 20 , 22 , 23 ).…”

Live-cell visualization of excitation energy dynamics in chloroplast thylakoid structures

“…In the grana, PSII and LHCII form protein super/megacomplexes arranged in semicrystalline arrays 10 13 14 , whose organizations are largely affected by light conditions and the composition of LHC proteins 15 16 17 18 19 . It has been suggested that the degree of PSII ordered array in grana affects the photosynthetic functions, such as energy transfer, electron transport, photoprotection, and protein repair processes 20 21 22 23 24 25 . It has also been suggested that the spatial segregation of PSI in stroma lamellae and PSII in grana prevents spillover of excitation energy from PSII to PSI and increases the rate of linear electron transport 26 27 28 .…”