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Atomic‐resolution structure of reduced cyanobacterial cytochrome c 6 with an unusual sequence insertion
Author(s) -
Bialek Wojciech,
Krzywda Szymon,
Jaskolski Mariusz,
Szczepaniak Andrzej
Publication year - 2009
Publication title -
the febs journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.981
H-Index - 204
eISSN - 1742-4658
pISSN - 1742-464X
DOI - 10.1111/j.1742-4658.2009.07150.x
Subject(s) - sequence (biology) , cytochrome f , resolution (logic) , crystallography , biology , chemistry , physics , stereochemistry , genetics , computer science , gene , artificial intelligence , photosystem i , chloroplast
The structure of the reduced form of cytochrome c 6 from the mesophilic cyanobacterium Synechococcus sp. PCC 7002 has been determined at 1.2 Å and refined to an R ‐factor of 0.107. This protein is unique among all known cytochromes c 6 , owing to the presence of an unusual seven‐residue insertion, KDGSKSL(44–50), which differs from the insertion found in the recently discovered plant cytochromes c 6A . Furthermore, the present protein is unusual because of its very high content (36%) of the smallest residues (glycine and alanine). The structure reveals that the overall fold of the protein is similar to that of other class I c ‐type cytochromes, despite the presence of the specific insertion. The insertion is located within the most variable region of the cytochrome c 6 sequence, i.e. between helices II and III. The first six residues [KDGSKS(44–49)] form a loop, whereas the last residue, Leu50, extends the N‐terminal beginning of helix III. Several specific noncovalent interactions are found inside the insertion, as well as between the insertion and the rest of the protein. The crystal structure contains three copies of the cytochrome c 6 molecule per asymmetric unit, and is characterized by an unusually high packing density, with solvent occupying barely 17.58% of the crystal volume.