Ultrastructural modeling of small angle scattering from photosynthetic membranes

Abstract

The last decade has seen a range of studies using non-invasive neutron and X-ray techniques to probe the ultrastructure of a variety of photosynthetic membrane systems. A common denominator in this work is the lack of an explicitly formulated underlying structural model, ultimately leading to ambiguity in the data interpretation. Here we formulate and implement a full mathematical model of the scattering from a stacked double bilayer membrane system taking instrumental resolution and polydispersity into account. We validate our model by direct simulation of scattering patterns from 3D structural models. Most importantly, we demonstrate that the full scattering curves from three structurally typical cyanobacterial thylakoid membrane systems measured in vivo can all be described within this framework. The model provides realistic estimates of key structural parameters in the thylakoid membrane, in particular the overall stacking distance and how this is divided between membranes, lumen and cytoplasmic liquid. Finally, from fitted scattering length densities it becomes clear that the protein content in the inner lumen has to be lower than in the outer cytoplasmic liquid and we extract the first quantitative measure of the luminal protein content in a living cyanobacteria.

Measuring the dynamic response of the thylakoid architecture in plant leaves by electron microscopy

“…The membrane thicknesses derived here (5.1 nm for dark-and 4.8 nm for light-adapted plants) are higher than the expected dimension for the thylakoid membrane. Neutron and x-ray scattering data for thylakoid membranes on leaves range from 3.4 to 4.8 nm (Jakubauskas et al, 2019). However, the light-induced shrinkage in membrane thickness derived in this study is statistically highly significant indicating that thinning of thylakoid membranes could control essential membrane functions.…”

“…The reason for this discrepancy is unclear as discussed in Ünnep et al (2014). However, a recent study where neutron scattering data were rigorously modeled revealed that the first Bragg peak (used to measure the grana repeat) is not a simple measure of the grana repeat distance (Jakubauskas et al, 2019).…”

Role of Protein-Water Interface in the Stacking Interactions of Granum Thylakoid Membranes—As Revealed by the Effects of Hofmeister Salts

“…In contrast, with 1.5 M NaSCN the decay of the periodic membrane ultrastructure was spectacularly accelerated; it was lost in less than 5 min ( Figure 7E). It is to be noted here, that these agents, including even NaCl, might have also induced changes in the microscopic structure of the membranes, affecting their form factor and thus their scattering length distributions, which could, in principle, be analyzed within an advanced mathematical model recently elaborated for cyanobacteria (Jakubauskas et al, 2019). This would require a detailed and systematic approach, paying also attention to the substantial differences between the ultrastructure of thylakoid membranes in cyanobacteria and higher plants; this is outside the scope of the present study.…”

Small-Angle X-Ray and Neutron Scattering on Photosynthetic Membranes

“…Part of such an experimental design is to estimate the scattering length densities of the sample material; however, calculating precise scattering length densities for biological systems is not straightforward, since the exact protein and lipid composition of the membrane, their volume fractions, protein H-D exchange degree, membrane-associated water content, and solvent composition need to be known. Some recently calculated scattering length density values of thylakoid membranes are given in Table 2 (Jakubauskas, 2016;Jakubauskas et al, 2019).…”

“…There are currently about 40-50 works published on scattering from photosynthetic systems-photosynthetic bacteria, diatoms and other algae and of course from higher plants. Small-angle scattering has been used to investigate structure and dynamic changes of thylakoid membrane systems of plants (Finean et al, 1953;Kratky et al, 1959;Kreutz and Menke, 1960a;Kreutz and Menke, 1960b;Kreutz and Menke, 1962;Kreutz, 1963a;Kreutz, 1963b;Kreutz, 1964;Sadler, 1976;Li, 1979;Sadler and Worcester, 1982a;Sadler and Worcester, 1982b;Diederichs et al, 1985;Garab et al, 1997;Kirkensgaard et al, 2009;Nagy, 2011;Nagy et al, 2011;Nagy et al, 2013;Ünnep et al, 2014b;Herdean et al, 2016;Ünnep et al, 2017;Zsiros et al, 2020;Ünnep et al, 2020), protists (Sadler et al, 1973;Worcester, 1976;Sadler and Worcester, 1982a), diatoms (Nagy et al, 2011;Nagy et al, 2012), photosynthetic bacteria (Pape et al, 1974;Hodapp and Kreutz, 1980;Liberton et al, 2013b;Ünnep et al, 2014a;Li et al, 2016;Stingaciu et al, 2016;Eyal et al, 2017;Jakubauskas et al, 2019), algae (Nagy et al, 2011;Nagy...…”