scholarly journals The PuhB Protein of Rhodobacter capsulatus Functions in Photosynthetic Reaction Center Assembly with a Secondary Effect on Light-Harvesting Complex 1

2005 ◽  
Vol 187 (4) ◽  
pp. 1334-1343 ◽  
Author(s):  
Muktak Aklujkar ◽  
Roger C. Prince ◽  
J. Thomas Beatty
Keyword(s):  
Reaction Center ◽  
Rhodobacter Capsulatus ◽  
Light Harvesting ◽  
Expression System ◽  
Photosynthetic Apparatus ◽  
Photosynthetic Reaction Center ◽  
Growth Conditions ◽  
Physiological Adaptation ◽  
Light Harvesting Complex ◽  
The Core

ABSTRACT The core of the photosynthetic apparatus of purple photosynthetic bacteria such as Rhodobacter capsulatus consists of a reaction center (RC) intimately associated with light-harvesting complex 1 (LH1) and the PufX polypeptide. The abundance of the RC and LH1 components was previously shown to depend on the product of the puhB gene (formerly known as orf214). We report here that disruption of puhB diminishes RC assembly, with an indirect effect on LH1 assembly, and reduces the amount of PufX. Under semiaerobic growth conditions, the core complex was present at a reduced level in puhB mutants. After transfer of semiaerobically grown cultures to photosynthetic (anaerobic illuminated) conditions, the RC/LH1 complex became only slightly more abundant, and the amount of PufX increased as cells began photosynthetic growth. We discovered that the photosynthetic growth of puhB disruption strains of R. capsulatus starts after a long lag period, which is due to physiological adaptation rather than secondary mutations. Using a hybrid protein expression system, we determined that the three predicted transmembrane segments of PuhB are capable of spanning a cell membrane and that the second transmembrane segment could mediate self-association of PuhB. We discuss the possible function of PuhB as a dimeric RC assembly factor.

scholarly journals The orf162b Sequence ofRhodobacter capsulatus Encodes a Protein Required for Optimal Levels of Photosynthetic Pigment-Protein Complexes

2000 ◽  
Vol 182 (19) ◽  
pp. 5440-5447 ◽  
Author(s):  
Muktak Aklujkar ◽  
Andrea L. Harmer ◽  
Roger C. Prince ◽  
J. Thomas Beatty
Keyword(s):  
Rhodobacter Capsulatus ◽  
Light Harvesting ◽  
Protein Complexes ◽  
Photosynthetic Pigment ◽  
Photosynthetic Apparatus ◽  
Coding Region ◽  
Reading Frame ◽  
Light Harvesting Complex ◽  
Pseudostationary Phase ◽  
Light Harvesting Complex Ii

ABSTRACT The orf162b sequence, the second open reading frame 3′ of the reaction center (RC) H protein gene puhA in theRhodobacter capsulatus photosynthesis gene cluster, is shown to be transcribed from a promoter located 5′ of puhA. A nonpolar mutation of orf162b was generated by replacing most of the coding region with an antibiotic resistance cartridge. Although the mutant strain initiated rapid photosynthetic growth, growth slowed progressively and cultures often entered a pseudostationary phase. The amounts of the RC and light harvesting complex I (LHI) in cells obtained from such photosynthetic cultures were abnormally low, but these deficiencies were less severe when the mutant was grown to a pseudostationary phase induced by low aeration in the absence of illumination. The orf162b mutation did not significantly affect the expression of apufB::lacZ translationally in-frame gene fusion under the control of the puf promoter, indicating normal transcription and translation of RC and LHI genes. Spontaneous secondary mutations in the strain with theorf162b disruption resulted in a bypass of the photosynthetic growth retardation and reduced the level of light harvesting complex II. These results and the presence of sequences similar to orf162b in other species indicate that the Orf162b protein is required for normal levels of the photosynthetic apparatus in purple photosynthetic bacteria.

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.

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