Purification and crystallization of photosynthetic reaction-center and light-harvesting I complex from Rhodospirillum rubrum

Department of Life Science, Tokyo Institute of Technology* National Institute of Advanced Industrial Science and Technology (AIST), Japan**
â—‹Takao Okabe* Yuichi Kato* Takashi Kumasaka* Takayuki Odahara**

The photosynthetic reaction-center and light-harvesting I complex (RC-LH1) of purple non-sulfur bacteria is composed of a hetero-oligomeric RC complex and LH1 antenna subunits encompassing RC. Although the structure of RC-LH1 from Rhodopseudomonas palustris has been determined at 4.8 Å resolution (PDB: 1PYH), the intimate mechanism of photosynthetic reactions is not elucidated yet. To investigate its structural details, we are studying on the crystallization of RC-LH1 from Rhodospirillum rubrum.
The protein solution was prepared by the method described previously.1) Rs. rubrum was cultured in five days and its chromatophore was collected from the fraction by French press. RC-LH1 was solubilized by DDM and purified by molecular-sieve chromatography. Crystallization was performed on the initial conditions determined based on the solubility diagram as a function of precipitant and protein concentrations,1) and also using sparse-matrix screening kits. The large crystals of RC-LH1 were obtained from the solution containing PEG400, MgCl2, DM (Figure), but only diffracted X-rays to low resolution. Searching more suitable conditions is in progress.
Ref: 1) Odahara, T. Biochim. Biophys. Acta 1660, 80 (2004).