Department of Life Science, Tokyo Institute of Technology^* National Institute of Advanced Industrial Science and Technology (AIST), Japan^**
○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).