Intrinsic Curvature Properties of Photosynthetic Proteins in Chromatophores

Abstract

In purple bacteria, photosynthesis is carried out on large indentations of the bacterial plasma membrane termed chromatophores. Acting as primitive organelles, chromatophores are densely packed with the membrane proteins necessary for photosynthesis, including light harvesting complexes LH1 and LH2, reaction center (RC), and cytochrome bc(1). The shape of chromatophores is primarily dependent on species, and is typically spherical or flat. How these shapes arise from the protein-protein and protein-membrane interactions is still unknown. Now, using molecular dynamics simulations, we have observed the dynamic curvature of membranes caused by proteins in the chromatophore. A membrane-embedded array of LH2s was found to relax to a curved state, both for LH2 from Rps. acidophila and a homology-modeled LH2 from Rb. sphaeroides. A modeled LH1-RC-PufX dimer was found to develop a bend at the dimerizing interface resulting in a curved shape as well. In contrast, the bc(1) complex, which has not been imaged yet in native chromatophores, did not induce a preferred membrane curvature in simulation. Based on these results, a model for how the different photosynthetic proteins influence chromatophore shape is presented.

Native architecture of the photosynthetic membrane from Rhodobacter veldkampii

“…Single particle analysis of the dimeric core complex clearly showed a curved side-view profile . Molecular dynamics simulation, using a model structure derived from this study, indicated core dimers may drive membrane curvature (Chandler et al, 2008;Hsin et al, 2009b). However, the present study unambiguously shows that monomeric RC-LH1-PufX complexes can be present in vesicular ICMs in Rb.…”

“…It was also shown that LH2 complexes can or cannot reveal tilt depending on the conditions (Gonçalves et al, 2005b). Computer simulation showed that specific arrays of LH2s, like seven hexagonally arranged domains, may drive the spherical curvature (Chandler et al, 2008(Chandler et al, , 2009). However, the assembly of LH2s and cores seems more random in the Rb.…”

“…These species feature vesicular ICMs (Oelze and Drews, 1972). It has therefore been advanced that the ICM shape is governed by the organization and interaction of the integral membrane proteins Jungas et al, 1999;Olsen et al, 2008), in particular the bending of S-shaped RC-LH1-PufX core dimers (Chandler et al, 2008;Hsin et al, 2009b;Qian et al, 2008;Scheuring et al, 2004c).…”

Peptide-induced membrane curvature in edge-stabilized open bilayers: A theoretical and molecular dynamics study

“…In addition to the analytical approach, we suggest the study of finite systems in coarse-grained (CG) MD simulations. Different to previous all-atom approaches of finite systems on a timescale of tens of nanoseconds, [6][7][8] we apply coarse-grained simulations with a tunable rim energy (see below) to gain useful insight into the action of, e.g., peptides on bilayer properties on the microsecond timescale.…”

Cell Biology of Prokaryotic Organelles

“…Cite this article as Cold Spring Harb Perspect Biol 2010;2:a000422 proteins and their long-range interactions with each other would be sufficient to produce curved membrane structures in vivo (Chandler et al 2008). Despite these convincing arguments in favor of a self-assembly model for chromatophore formation, it is possible that other factors may be involved in the process.…”