scholarly journals Effect of oxygen on levels of mRNA coding for reaction-centre and light-harvesting polypeptides of Rhodobacter sphaeroides

1987 ◽  
Vol 247 (2) ◽  
pp. 489-492 ◽  
Author(s):  
C N Hunter ◽  
M K Ashby ◽  
S A Coomber
Keyword(s):  
Rhodobacter Sphaeroides ◽  
Light Harvesting ◽  
Photosynthetic Apparatus ◽  
Maximum Level ◽  
Reaction Centre ◽  
Puf Operon ◽  
Effect Of Oxygen

The relative levels of mRNA for the reaction-centre L and M subunits, B875 (LH1) alpha and beta polypeptides and B800-850 (LH2) alpha and beta polypeptides, have been measured during pigment induction of Rhodobacter sphaeroides. Over the 6 h of the experiment, bacteriochlorophyll levels increased by at least 100-fold. No transcripts for photosynthetic components were detectable at the start of induction; after 2 h the levels of transcripts from the puf operon (encoding reaction-centre and B875 subunits) had reached the maximum; these transcripts were 2.7 and 0.5 kb respectively. The transcript for the puc operon (B800-850 complex) was estimated to be 0.55 kb and reached a maximum level after 6 h. These results are consistent with the proposal that, during the assembly of the photosynthetic apparatus, the synthesis of B875 reaction-centre aggregates precedes that of the major antenna, B800-850.

scholarly journals Cryo-EM structure of the Rhodobacter sphaeroides RC-LH1 core monomer complex at 2.5 Å

2021 ◽  
Author(s):  
Pu Qian ◽  
David JK Swainsbury ◽  
Tristan Ian Croll ◽  
Jack H Salisbury ◽  
Elizabeth C Martin ◽  
...  
Keyword(s):  
Rhodobacter Sphaeroides ◽  
Light Harvesting ◽  
Ring Structure ◽  
Bacterial Photosynthesis ◽  
Reaction Centre ◽  
Cytochrome Bc1 Complex ◽  
Protein Subunit ◽  
Proton Transfers ◽  
Monomeric Complex ◽  
Essential Components

Reaction centre light-harvesting 1 (RC-LH1) complexes are the essential components of bacterial photosynthesis. The membrane-intrinsic LH1 complex absorbs light and the energy migrates to an enclosed RC where a succession of electron and proton transfers conserves the energy as a quinol, which is exported to the cytochrome bc1 complex. In some RC-LH1 variants quinols can diffuse through small pores in a fully circular, 16-subunit LH1 ring, while in others missing LH1 subunits create a gap for quinol export. We used cryogenic electron microscopy to obtain a 2.5 Å resolution structure of one such RC-LH1, a monomeric complex from Rhodobacter sphaeroides. The structure shows that the RC is partly enclosed by a 14-subunit LH1 ring in which each αβ heterodimer binds two bacteriochlorophylls and, unusually for currently reported complexes, two carotenoids rather than one. Although the extra carotenoids confer an advantage in terms of photoprotection and light harvesting, they could block small pores in the LH1 ring and impede passage of quinones, necessitating a mechanism to create a dedicated quinone channel. The structure shows that two transmembrane proteins play a part in stabilizing an open ring structure; one of these components, the PufX polypeptide, is augmented by a hitherto undescribed protein subunit we designate as protein-Y, which lies against the transmembrane regions of the thirteenth and fourteenth LH1α polypeptides. Protein-Y prevents LH1 subunits 11-14 adjacent to the RC QB site from bending inwards towards the RC and, with PufX preventing complete encirclement of the RC, this pair of polypeptides ensures unhindered

scholarly journals Dichotomous disorder model for single light-harvesting complexes

2019 ◽  
Vol 58 (4) ◽  
Author(s):  
Danielis Rutkauskas
Keyword(s):  
Light Harvesting ◽  
Purple Bacteria ◽  
Photosynthetic Apparatus ◽  
Theoretical Research ◽  
Spectral Signature ◽  
Reaction Centre ◽  
Excitation Energies ◽  
Light Harvesting Complexes ◽  
Protein Scaffold ◽  
Migration Pathways

Photosynthetic organisms conserve the captured energy of solar radiation into stable chemical forms. To do so, they have evolved specialized systems of pigment–protein complexes consisting of light-harvesting antennas and reaction centres. Photosynthetic antennas contain remarkably dense arrangements of light-absorbing pigments held by the protein scaffold, and their function is to absorb light and funnel the excitation energy to the reaction centre. Decades of experimental and theoretical research resulted in a detailed understanding of the energy migration pathways within the photosynthetic apparatus. The key parameters determining the excitation relaxation and transfer are inter-pigment coupling and energetic disorder or non-equality of excitation energies at equivalent pigment sites due to the interaction with the disordered protein scaffold. Circularly symmetric light-harvesting antennas from purple bacteria present a beautiful example of the interplay between these parameters. The spectral signature of this interplay could be observed with the single-molecule fluorescence microscopy techniques. The results of these measurements were interpreted with an intuitively clear dichotomous model of disorder of pigment site energies.

Macroorganisation and flexibility of thylakoid membranes

2019 ◽  
Vol 476 (20) ◽  
pp. 2981-3018 ◽  
Author(s):  
Petar H. Lambrev ◽  
Parveen Akhtar
Keyword(s):  
Light Harvesting ◽  
Current Knowledge ◽  
Three Dimensional ◽  
Photosynthetic Apparatus ◽  
Dynamic Responses ◽  
State Transitions ◽  
Photochemical Quenching ◽  
Light Harvesting Complex ◽  
Complex Ii ◽  
Light Harvesting Complex Ii

Abstract The light reactions of photosynthesis are hosted and regulated by the chloroplast thylakoid membrane (TM) — the central structural component of the photosynthetic apparatus of plants and algae. The two-dimensional and three-dimensional arrangement of the lipid–protein assemblies, aka macroorganisation, and its dynamic responses to the fluctuating physiological environment, aka flexibility, are the subject of this review. An emphasis is given on the information obtainable by spectroscopic approaches, especially circular dichroism (CD). We briefly summarise the current knowledge of the composition and three-dimensional architecture of the granal TMs in plants and the supramolecular organisation of Photosystem II and light-harvesting complex II therein. We next acquaint the non-specialist reader with the fundamentals of CD spectroscopy, recent advances such as anisotropic CD, and applications for studying the structure and macroorganisation of photosynthetic complexes and membranes. Special attention is given to the structural and functional flexibility of light-harvesting complex II in vitro as revealed by CD and fluorescence spectroscopy. We give an account of the dynamic changes in membrane macroorganisation associated with the light-adaptation of the photosynthetic apparatus and the regulation of the excitation energy flow by state transitions and non-photochemical quenching.

scholarly journals Origin of the mRNA stoichiometry of the puf operon in Rhodobacter sphaeroides.

1986 ◽  
Vol 261 (22) ◽  
pp. 10366-10374 ◽  
Author(s):  
Y S Zhu ◽  
P J Kiley ◽  
T J Donohue ◽  
S Kaplan
Keyword(s):  
Rhodobacter Sphaeroides ◽  
Puf Operon
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