Characteristics of fibers formed by cytochrome c and induced by anionic phospholipids

Recent publications described the formation of millimeter-length fibers by diverse lipid-binding proteins (e.g., histone H1, cytochrome c, indolicidin, and endostatin) when they are mixed with 80:20 phosphatidylcholine/phosphatidylserine vesicles. Further, these fibers displayed amyloid characteristics when stained with Congo Red. In the study presented here, we found by FTIR the amide I absorption band to reveal significant variation in fibers formed by cytochrome c, with some consisting of cytochrome c in a nativelike conformation and some exhibiting strong amyloid (beta-sheet) characteristics. Protein structure also varied from amyloid to nearly native within single fibers. Fibers were frequently blue or bluish and sometimes iridescent, likely due to interference of light in the fibers. The amyloid-type amide I band was observed for blue fibers only. AFM shows that fibers consist of smaller 3-4 nm diameter fibers with 10 nm lateral spacing.