Cloning, expression and purification of cytochrome c₆ from the brown alga Hizikia fusiformis and complete X-ray diffraction analysis of the structure

The primary sequence of cytochrome c₆ from the brown alga Hizikia fusiformis has been determined by cDNA cloning and the crystal structure has been solved at 1.6 Å resolution. The crystal belonged to the tetragonal space group P4₁2₁2, with unit-cell parameters a = b = 84.58, c = 232.91 Å and six molecules per asymmetric unit. The genome code, amino-acid sequence and crystal structure of H. fusiformis cytochrome c₆ were most similar to those of red algal cytochrome c₆. These results support the hypothesis that brown algae acquired their chloroplasts via secondary endosymbiosis involving a red algal endo­symbiont and a eukaryote host.