Energetic cost of the entatic state of cytochrome c quantified

June 23, 2017 by Bob Yirka, Phys.org report
A change in the active-site conformation turns cytochrome c from an electron shuttle in respiration to a peroxidase enzyme for apoptosis. Credit: (c) Science  23 Jun 2017: Vol. 356, Issue 6344, pp. 1236 , DOI: 10.1126/science.aan5587

(Phys.org)—A team of researchers at Stanford University has used ultrafast x-ray absorption and emission spectroscopy to quantify the entatic state of cytochrome c. In their paper published in the journal Science, the group outlines their procedure and what they learned. Kara Bren and Emma Raven with the University of Rochester and University of Leicester respectively offer a Perspective piece on the work done by the team in the same journal issue, and outline some of the implications regarding the role that the protein plays in cell life and death.

Cytochrome c is a protein that exists in many plants, animals and unicellular organisms. In humans, its main purposes are ferrying electrons in mitochondria and assisting with apoptosis (normal cell death and the processes surrounding it.) These two functions have been shown in prior efforts to rely on the position of methionine residue. When sulfur works with iron, the protein is ready to transfer electrons. Otherwise, it engages in peroxidase activities. In this new effort, the researchers sought to better understand the energetics of the protein by probing the iron and sulfur bond. Entatic states, Bren and Raven point out, are very important in bioinorganic chemistry—it actually translates to something that is stretched when subjected to tension.

To better understand the bond between the two elements, the researchers temporarily forced them apart using a Linac Coherent Light Source X-ray free electron laser and then timed how long it took the two components to reform using iron X-ray . They found that the environment in which they existed boosted bond strength by four kilocalories per mole, which was enough to allow the protein to toggle between its functional states and to quantify the energy cost of the entatic state.

As Bren and Raven note, the results of the study have implications regarding the role that cytochrome plays in respiration, which they relate to living and apoptosis, which they relate to death. To promote continued living the helps to maintain a certain reduction potential. For apoptosis, the entatic state is disrupted allowing peroxidase activity to be enhanced.

Explore further: Potential therapeutic target for Parkinson's disease

More information: Metalloprotein entatic control of ligand-metal bonds quantified by ultrafast x-ray spectroscopy, Science (2017). science.sciencemag.org/cgi/doi … 1126/science.aam6203

The multifunctional protein cytochrome c (cyt c) plays key roles in electron transport and apoptosis, switching function by modulating bonding between a heme iron and the sulfur in a methionine residue. This Fe–S(Met) bond is too weak to persist in the absence of protein constraints. We ruptured the bond in ferrous cyt c using an optical laser pulse and monitored the bond reformation within the protein active site using ultrafast x-ray pulses from an x-ray free-electron laser, determining that the Fe–S(Met) bond enthalpy is ~4 kcal/mol stronger than in the absence of protein constraints. The 4 kcal/mol is comparable with calculations of stabilization effects in other systems, demonstrating how biological systems use an entatic state for modest yet accessible energetics to modulate chemical function.

Related Stories

Potential therapeutic target for Parkinson's disease

June 7, 2017

Investigations by scientists in Japan illustrate how the loss of a key mitochondrial protein facilitates the progression of Parkinson's disease. The findings are published in Nature Communications (June 2017).

Electrons use DNA like a wire for signaling DNA replication

February 24, 2017

In the early 1990s, Jacqueline Barton, the John G. Kirkwood and Arthur A. Noyes Professor of Chemistry at Caltech, discovered an unexpected property of DNA—that it can act like an electrical wire to transfer electrons quickly ...

Recommended for you

New battery gobbles up carbon dioxide

September 21, 2018

A new type of battery developed by researchers at MIT could be made partly from carbon dioxide captured from power plants. Rather than attempting to convert carbon dioxide to specialized chemicals using metal catalysts, which ...

Scientists solve the golden puzzle of calaverite

September 21, 2018

Scientists from Russia and Germany have shed light on the crystalline structure of calaverite, foretelling the existence of a new gold compound previously unknown to chemists. The results of their study were published in ...


Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.