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J. Biol. Chem., Vol. 278, Issue 26, 23678-23685, June 27, 2003

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A Reaction Center-Light-harvesting 1 Complex (RC-LH1) from a Rhodospirillum rubrum Mutant with Altered Esterifying Pigments

CHARACTERIZATION BY OPTICAL SPECTROSCOPY AND CRYO-ELECTRON MICROSCOPY^*

Pu Qian, Hugh A. Addlesee , Alexander V. Ruban, Peiyi Wang, Per A. Bullough and C. Neil Hunter 

From the Krebs Institute, Department of Molecular Biology and Biotechnology, University of Sheffield, Firth Court, Western Bank, Sheffield S10 2TN, United Kingdom

Introduction of the bchP gene from Rhodobacter sphaeroides encoding geranylgeranyl reductase into Rhodospirillum rubrum alters the esterification of the bacteriochlorophylls so that phytol is used instead of geranylgeraniol. The resulting transconjugant strain of Rs. rubrum grows photosynthetically, showing that phytolated Bchla can substitute for the native pigment in both the reaction center (RC) and the light-harvesting 1 (LH1) complexes. This genetic manipulation perturbs the native carotenoid biosynthetic pathway; several biosynthetic intermediates are assembled into the core complex and are capable of energy transfer to the bacteriochlorophylls. RC-LH1 complexes containing phytolated Bchla were analyzed by low temperature absorption and fluorescence spectroscopy and circular dichroism. These show that phytolated Bchls can assemble in vivo into the photosynthetic apparatus of Rs. rubrum and that the newly introduced phytol tail provokes small perturbations to the Bchls within their binding sites in the LH1 complex. The RC-LH1 core complex was purified from membranes and reconstituted into well ordered two-dimensional crystals with a p42₁2 space group. A projection map calculated to 9 Å shows clearly that the LH1 ring from the mutant is composed of 16 subunits that surround the reaction center and that the diameter of this complex is in close agreement with that of the wild-type LH1 complex.

Received for publication, March 18, 2003 , and in revised form, April 28, 2003.

^* This research work was supported by grants from the Biotechnology and Biological Sciences Research Council of the United Kingdom and the Joint Infrastructure Fund. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

Present address: Crusade Laboratories, Institute of Neurological Sciences, Southern General Hospital, Glasgow G51 4TF.

To whom correspondence should be addressed. Tel.: 0114-222-4191; Fax: 0114-222-2711; E-mail: c.n.hunter{at}sheffield.ac.uk

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