PROTEIN FOLDING AND PROTEIN EVOLUTION : COMMON FOLDING NUCLEUS IN DIFFERENT SUBFAMILIES OF C-TYPE CYTOCHROMES?

摘要: Abstract Amino acid sequences of seven subfamilies cytochromes c (mitochondrial c, c1; chloroplast c6, cf; bacterial c2, c550, c551; in total 164 sequences) have been compared. Despite extensive homology within eukaryotic subfamilies, between different is very weak. Other than the three heme-binding residues (Cys13, Cys14, His18, numeration horse cytochrome c) there are only four positions which conserved all subfamilies: Gly/Ala6, Phe/Tyr10, Leu/Val/Phe94 and Tyr/Trp/Phe97. In 17 with known 3D-structures, these form a network contacts (6–94, 6–97, 10–94, 10–97 94–97). Especially strong contact aromatic groups 10 97, corresponds to 13 interatomic contacts. As 6, 94, 97 (i, i + 4) 3) N C-terminal helices, respectively, above mentioned system consists mainly one turn N-terminal helix helix. The importance interfaces helices has confirmed by existence both equilibrium kinetic molten globule-like folding intermediates, as well mutational evidence that involved tight packing C-helices. Since not heme binding no other apparent functional role, their conservation highly diverged suggests they critical for protein folding. author assumes common nucleus c-type cytochromes.