Heme Is Not Required for Aquifex aeolicus Cytochrome c₅₅₅ Polypeptide Folding
2009
YAMANAKA, Masaru | MITA, Hajime | YAMAMOTO, Yasuhiko | SAMBONGI, Yoshihiro
In cytochrome c, it has been supposed that heme must bind to the apo polypeptide for structure formation. We constructed a C12A/C15A variant of hyperthermophilic Aquifex aeolicus cytochrome c ₅₅₅ (AA c ₅₅₅) in which the covalently heme-binding Cys residues were replaced by Ala, and characterized its molecular features. The apo C12A/C15A variant had almost the same helical content as holo AA c ₅₅₅, and spontaneously incorporated heme in vitro with no helical content change. These results suggest that the apo AA c ₅₅₅ polypeptide is intrinsically structured without heme binding, this being the first case of a cytochrome c polypeptide. This finding provides a new suggestion as to cytochrome c formation, that heme is not necessarily required for cytochrome c polypeptide folding.
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