Molecule of the Month: Cytochrome bc1
A flow of electrons powers proton pumps in cellular respiration and photosynthesis
Exploring the Structure
Cytochrome bc1 (PDB entries 1ntz, 1kyo and 1bcc)
The structures of cytochrome bc1 revealed the path of electrons and the sites for binding of ubiquinol, and also a surprise. The path that leads to cytochrome c passes through an iron-sulfur cluster and then to a heme, which then passes the electron to cytochrome c. The first structures showed that the protein chain that holds the iron sulfur cluster flips back and forth, first bumping up against the ubiquinol and picking up the electron, then moving down to pass the electron to the heme. To take a look at this motion, click on the image here for an interactive Jmol.
Topics for Further Discussion
- Many drugs have been discovered that bind to the ubiquinol sites in cytochrome bc1. You can find these structures in the PDB, and explore the similarity of the drugs to ubiquinol.
- Cytochrome b6f uses a similar mechanism for linking electron transport to proton transport. Compare the two complexes, and notice that cytochrome b6f has a few extra cofactors. Scientists are still sorting out what these cofactors are doing--do you have any ideas?
Related PDB-101 Resources
- Browse Nanotechnology
- Browse Biology of Plants
- Browse Biological Energy
- A. R. Crofts (2004) The cytochrome bc1 complex: function in the context of structures. Annual Review of Physiology 66, 689-733
- J. L. Cape, M. K. Bowman and D. M. Kramer (2006) Understanding the cytochrome bc complexes by what they don't do. The Q-cycle at 30. Trends in Plant Science 11, 46-55.
- D. Baniulis, E. Yamashita, H. Zhang, S. S. Hasan and W. A. Cramer (2008) Structure-function of the cytochrome b6f complex. Photochemistry and Photobiology 84, 1349-1358.
May 2011, David Goodsellhttp://doi.org/10.2210/rcsb_pdb/mom_2011_5