Journal of Biochemistry Advance Access originally published online on December 13, 2006
Journal of Biochemistry 2007 141(1):121-126; doi:10.1093/jb/mvm015
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© 2006 The Japanese Biochemical Society.
Process of Maturation of Tetraheme Cytochrome c3 in a Shewanella Expression System

1Institute for Protein Research, Osaka University, 3-2 Yamadaoka, Suita, Osaka 565-0871, and 2Institute for Bioinformatics Research and Development, Japan Science and Technology Agency, 5-3 Yonbancho, Chiyoda, Tokyo 102-8666, Japan
*To whom correspondence should be addressed. Tel: +81-6-6879-8597. Fax: +81-6-6879-8599. E-mail: akutsu{at}protein.osaka-u.ac.jp
Received September 25, 2006; Accepted November 23, 2006
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The process of maturation of multiheme proteins is not yet well known, while that of monoheme ones has been relatively well investigated. Two kinds of partly unfolded tetraheme cytochrome c3 were obtained on overexpression in Shewanella oneidensis TSP-C. These proteins were characterized by circular dichroism and nuclear magnetic resonance spectroscopy. It turned out that the tetraheme architecture, and the fifth and sixth ligand coordination are almost mature, while some parts of the polypeptide are unfolded. The unfolded residues are mainly located in the helix-rich region including heme attachment and axial ligand sites. This suggests that the formation of the heme architecture, coordination of axial ligands and helix formation should be coupled with each other. While the former two can take place automatically, the helix formation would need help by a chaperone-like function in the cytochrome c maturation (Ccm) machinery. It must be working in sulphate-reducing bacteria. The Ccm machinery in S. oneidensis is likely insufficient to help the maturation of proteins with cyclic heme architectures. This is the first report providing an insight into the process of maturation of tetraheme cytochrome c3.
Key Words: chaperon, cytochrome c3, cytochrome c maturation, folding, heme architecture, sulphate-reducing bacterium
Abbreviations: cyt, cytochrome; SRB, sulphate-reducing bacteria; DvMF, Desulfovibrio vulgaris Miyazaki F; Ccm, cytochrome c maturation; NaPi, sodium phosphate; CD, circular dichroism; NMR, nuclear magnetic resonance; Gdn-HCl, guanidine hydrochloride
Current address: Department of Chemistry, Northwest University, China.