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Investigation of Rhodobacter capsulatus PufX interactions in the core complex of the photosynthetic apparatus

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Abstract

The photosynthetic apparatus of purple bacteria in the genus Rhodobacter includes a core complex consisting of the reaction centre (RC), light-harvesting complex 1 (LH1), and the PufX protein. PufX modulates LH1 structure and facilitates photosynthetic quinone/quinol exchange. We deleted RC/LH1 genes in pufX + and pufX ++ (merodiploid) strains of Rhodobacter capsulatus, which reduced PufX levels regardless of pufX gene copy number and location. Photosynthetic growth of RC-only strains and independent assembly kinetics of the RC and LH1 were unaffected by pufX merodiploidy, but the absorption spectra of strains expressing the RC plus either LH1 α or β indicated that PufX may influence bacteriochlorophyll binding environments. Significant self-association of the PufX transmembrane segment was detected in a hybrid protein expression system, consistent with a role of PufX in core complex dimerization, as proposed for other Rhodobacter species. Our results indicate that in R. capsulatus PufX has the potential to be a central, homodimeric core complex component, and its cellular level is increased by interactions with the RC and LH1.

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Abbreviations

BChl:

bacteriochlorophyll a

Bphe:

bacteriopheophytin a

cyt b/c 1 :

cytochrome b/c 1 complex

LH1:

light-harvesting complex 1

LH2:

light-harvesting complex 2

ICM:

intracytoplasmic membrane system

RC:

reaction centre

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Acknowledgements

We thank G. Drews and G. Klug for plasmids, W.␣Russ and D. Engelman for the TOXCAT materials, J. Beckwith for strain MM39, and P. Qian and C. N. Hunter for helpful discussions. M.A. was supported in part by fellowships from UBC and by an NSERC (Canada) scholarship. This research was funded by an NSERC grant to J.T.B.

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  1. Muktak Aklujkar

    Present address: Department of Microbiology, University of Massachusetts Amherst, 203 Morrill IVN, North Pleasant Street, Amherst, MA, 01003, USA

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  1. Department of Microbiology and Immunology, University of British Columbia, 2350 Health Sciences Mall, V6T 1Z3, Vancouver, BC, Canada

    Muktak Aklujkar & J. Thomas Beatty

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  1. Muktak Aklujkar
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Correspondence to Muktak Aklujkar.

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Aklujkar, M., Beatty, J.T. Investigation of Rhodobacter capsulatus PufX interactions in the core complex of the photosynthetic apparatus. Photosynth Res 88, 159–171 (2006). https://doi.org/10.1007/s11120-006-9047-y

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