Purification, crystallization and preliminary crystallographic investigations of selenium-containing phycocyanin from selenium-rich algae (Spirulina platensis)

The selenium-containing phycocyanin from the selenium-rich algae (Spirulina platensis) has been crystallized in two crystal forms by the hanging-drop vapor diffusion techniques. A chromatographic procedure of gel filtration and anion exchange was used for purification. Form I crystal with space group P2₁ and cell parameters a =108.0 Å, b= 117.0 Å, c = 184.0Å, β= 90.2° and 12(αβ) units in the asymmetric unit was obtained by using (NH₄)₂SO₄ as precipitant. These crystals diffract up to 2.8 Å. Form II crystal obtained by using PEG4000 as precipitant belongs to space group P6₃ with unit cell constants a = 155.0 Å, c = 40.3 Å, γ =120.0° and one(αβ) unit in the asymmetric unit. The crystals diffract beyond 2.9 Å. The possible stacking forms of phycocyanin molecules in the first crystal form were discussed.