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Issue 12, 2005
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The assembly and organisation of photosynthetic membranes in Rhodobacter sphaeroides

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Abstract

Recent AFM data (S. Bahatyrova, R. N. Frese, C. A. Siebert, J. D. Olsen, K. O. van der Werf, R. van Grondelle, R. A. Niederman, P. A. Bullough, C. Otto and C. N. Hunter, Nature, 2004, 430, 1058–1062, ) demonstrate that mature photosynthetic membranes of R. sphaeroides are composed of rows of dimeric RC-LH1-PufX complexes with some LH2 complexes ‘sandwiched’ between these rows of core complexes, and others in discrete LH2-only domains which might form the light-responsive complement of the LH2 antenna. The present work applies membrane fractionation, radiolabelling and LDS-PAGE techniques to investigate the response of R. sphaeroides to lowered light intensity. The kinetics underlying this adaptation to low light conditions were revealed by radiolabelling with the bacteriochlorophyll (bchl) biosynthetic precursor, δ-aminolevulinate, which allowed us to measure only the bchls synthesised after the light intensity shift. We show that (1) the increase in LH2 antenna size is mainly restricted to the mature ICM membrane fraction, and the antenna composition of the precursor upper pigmented band (UPB) membrane remains constant, (2) the precursor UPB membrane is enriched in bchl synthase, the terminal enzyme of the bchl biosynthetic pathway, and (3) the LH2 and the complexes of intermediate migration in LDS-PAGE exhibit completely different labelling kinetics. Thus, new photosynthetic complexes, mainly LH2, are synthesised and assembled at the membrane initiation UPB sites, where the LH2 rings pack between the rows of dimeric cores fostering new LH2–LH1 interactions. Mature membranes also assemble new LH2 rings, but in this case the ‘sandwich’ regions between the rows of core dimers are already fully occupied and the bulk antenna pool is the favoured location for these new LH2 complexes.

Graphical abstract: The assembly and organisation of photosynthetic membranes in Rhodobacter sphaeroides

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Publication details

The article was received on 03 May 2005, accepted on 20 Jul 2005 and first published on 19 Aug 2005


Article type: Paper
DOI: 10.1039/B506099K
Citation: Photochem. Photobiol. Sci., 2005,4, 1023-1027
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    The assembly and organisation of photosynthetic membranes in Rhodobacter sphaeroides

    C. N. Hunter, J. D. Tucker and R. A. Niederman, Photochem. Photobiol. Sci., 2005, 4, 1023
    DOI: 10.1039/B506099K

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