Crystal structure of low-potential cytochrome c ₅₄₉ from Synechocystis sp. PCC 6803 at 1.21 Å resolution

Abstract.

The crystal structure of low-potential cytochrome c ₅₄₉, an extrinsic component of the photosystem II (PS II) from Synechocystis sp. PCC 6803, was obtained directly from single-wavelength 1.21 Å resolution diffraction data. This is the first monodomain bis-histidinyl monoheme cytochrome c to be structurally characterized. The extended N-terminal region of c ₅₄₉ builds up a two-strand antiparallel β-sheet in a hairpin motif, which extends through two molecules owing to crystal packing. Both peptide termini are involved in crystal contacts, which may explain their protrusion out of the globular fold. The C-terminus is preceded by a 9 Å-long hydrophobic finger extending from a positively charged base and could be involved in PSII interactions, as well as a protruding negative patch built by a set of conserved acidic residues among c ₅₄₉ sequences.