Structural Entities Associated with Different Lipid Phases of Plant Thylakoid Membranes—Selective Susceptibilities to Different Lipases and Proteases

Abstract

It is well established that plant thylakoid membranes (TMs), in addition to a bilayer, contain two isotropic lipid phases and an inverted hexagonal (HII) phase. To elucidate the origin of non-bilayer lipid phases, we recorded the 31P-NMR spectra of isolated spinach plastoglobuli and TMs and tested their susceptibilities to lipases and proteases; the structural and functional characteristics of TMs were monitored using biophysical techniques and CN-PAGE. Phospholipase-A1 gradually destroyed all 31P-NMR-detectable lipid phases of isolated TMs, but the weak signal of isolated plastoglobuli was not affected. Parallel with the destabilization of their lamellar phase, TMs lost their impermeability; other effects, mainly on Photosystem-II, lagged behind the destruction of the original phases. Wheat-germ lipase selectively eliminated the isotropic phases but exerted little or no effect on the structural and functional parameters of TMs—indicating that the isotropic phases are located outside the protein-rich regions and might be involved in membrane fusion. Trypsin and Proteinase K selectively suppressed the HII phase—suggesting that a large fraction of TM lipids encapsulate stroma-side proteins or polypeptides. We conclude that—in line with the Dynamic Exchange Model—the non-bilayer lipid phases of TMs are found in subdomains separated from but interconnected with the bilayer accommodating the main components of the photosynthetic machinery.

Cobra Venom Cytotoxins as a Tool for Probing Mechanisms of Mitochondrial Energetics and Understanding Mitochondrial Membrane Structure

“…In our view, this area of science has not received the necessary attention for over half a century. Nonetheless, reports from the past twenty years have convincingly highlighted the importance of non-bilayer lipid structures in modulating the structure and functions of not only mitochondrial membranes but also thylakoid membranes [2,4,15,20,21,26,36,37,53,[117][118][119][120][121][122][123][124]. For the latest views regarding the role of the non-bilayer phase in energy-transducing membranes, we direct readers to peruse the most recent comprehensive review cited below, which describes in detail how non-bilayer structures affect the structural architecture and functions of mitochondrial and thylakoid membranes [21].…”

Editorial

“…The physiological significance of non-bilayer lipids in the thylakoid and, in fact, all energy-converting membranes, has remained enigmatic. Győző and coworkers, using different spectroscopic tools, especially 31 P-NMR, have shown the dynamic lipid polymorphism in the chloroplast thylakoid membranes with the co-existence of lamellar and non-lamellar, or non-bilayer phases and their response to external environmental factors (Krumova et al 2008, Garab et al 2016Kotakis et al 2018, Dlouhý et al 2020, 2022a. A dynamic exchange model (DEM) was proposed, according to which non-bilayer phases play key roles in the lipid exchange between membrane compartments and several enzymatic processes not only in photosynthesis but also in respiration (Garab et al 2017(Garab et al , 2022Gasanoff et al 2021, Dlouhý et al 2022b.…”