Mimicking nature, scientists can now extend redox potentials

November 04, 2009

CHAMPAIGN, Ill. -- New insight into how nature handles some fundamental processes is guiding researchers in the design of tailor-made proteins for applications such as artificial photosynthetic centers, long-range electron transfers, and fuel-cell catalysts for energy conversion.

From rusting iron to forest fires to the beating of a human heart, oxidation-reduction reactions, which transfer electrons from one atom to another, are at the heart of many chemical and biological processes. Each process requires a particular redox potential, just as different electronic devices can require their own special battery.

How nature fine-tunes these potentials over a broad range with little change to the protein's electron-transfer properties or efficiency has largely remained a mystery.

Now, a team led by University of Illinois chemistry professor Yi Lu has unearthed nature's secret, and has utilized it to their advantage. The researchers describe their work in a paper to appear in the Nov. 5 issue of the journal Nature. "We show that two important interactions, hydrophobicity (water repelling) and hydrogen bonding, are capable of fine-tuning the reduction potential of a particular class of copper-containing proteins called cupredoxins," Lu said. "We extended the range both above and below what had previously been found in nature."

Lu, graduate student and lead author Nicholas M. Marshall, and their collaborators also show that the effects of hydrophobicity and hydrogen bonding are additive, which offers additional control and extends the range of redox (short for oxidation-reduction reaction) potentials beyond what nature, by itself, provides.

Previously, to cover a wide potential range, scientists had to use several different redox agents in conjunction. This made it difficult, if not impossible, to tune the redox potentials without changing other electron transfer properties or the efficiency.

Also, stable, water-soluble redox agents are rare, Lu said, and those that are available have a limited potential range. "Consequently, there is a huge demand for efficient, water-soluble redox agents with a wide potential range for environmentally friendly aqueous or biochemical studies," he said.

To unlock nature's secret, Lu's team studied the behavior of the cupredoxin, azurin. Cupredoxins are redox-active copper proteins that play crucial roles in many important processes, such as photosynthesis and cell signaling. Cupredoxins use a single redox-active center, whose reduction potential is tunable without compromising the structure and electron transfer properties of the protein.

The researchers found that two interactions - hydrophobicity and hydrogen bonding - can selectively raise or lower azurin's redox potential. The interactions occur not in the metalloprotein's innermost, primary core, but in a secondary sphere that surrounds the primary core.

Increasing the hydrophobicity in the secondary sphere can significantly increase the redox potential, the researchers report. The more this secondary region repels water, the more the overall charge on the copper ion becomes destabilized and the higher the potential becomes.

The effect of the hydrogen bonding interaction is subtler than the effect of hydrophobicity, Lu said. Hydrogen bonding can either increase or decrease electron densities around a residue that binds the copper ion in azurin, making the copper ion either easier or harder to reduce and thus slightly changing the redox potential.

"This was nature's secret," Lu said. "That by adjusting the hydrophobicity and the hydrogen bonding, we can raise or lower the redox potential, without changing the protein's electron-transfer properties or decreasing the protein's efficiency."

The result is a tailor-made redox agent that can be set with a very high potential, a very low potential, or with a potential somewhere in between.

"This unprecedented level of control over an electron-transfer protein was achieved by mapping out the major interactions," Lu said, "an approach that may apply to other redox proteins of interest, as well."
-end-
Lu is affiliated with the university's Beckman Institute, the departments of biochemistry, bioengineering, and materials science and engineering, the Frederick Seitz Materials Research Laboratory, and the Center of Biophysics and Computational Biology. The National Science Foundation and the National Institutes of Health funded the work.

University of Illinois at Urbana-Champaign

Related Proteins Articles from Brightsurf:

New understanding of how proteins operate
A ground-breaking discovery by Centenary Institute scientists has provided new understanding as to the nature of proteins and how they exist and operate in the human body.

Finding a handle to bag the right proteins
A method that lights up tags attached to selected proteins can help to purify the proteins from a mixed protein pool.

Designing vaccines from artificial proteins
EPFL scientists have developed a new computational approach to create artificial proteins, which showed promising results in vivo as functional vaccines.

New method to monitor Alzheimer's proteins
IBS-CINAP research team has reported a new method to identify the aggregation state of amyloid beta (Aβ) proteins in solution.

Composing new proteins with artificial intelligence
Scientists have long studied how to improve proteins or design new ones.

Hero proteins are here to save other proteins
Researchers at the University of Tokyo have discovered a new group of proteins, remarkable for their unusual shape and abilities to protect against protein clumps associated with neurodegenerative diseases in lab experiments.

Designer proteins
David Baker, Professor of Biochemistry at the University of Washington to speak at the AAAS 2020 session, 'Synthetic Biology: Digital Design of Living Systems.' Prof.

Gone fishin' -- for proteins
Casting lines into human cells to snag proteins, a team of Montreal researchers has solved a 20-year-old mystery of cell biology.

Coupled proteins
Researchers from Heidelberg University and Sendai University in Japan used new biotechnological methods to study how human cells react to and further process external signals.

Understanding the power of honey through its proteins
Honey is a culinary staple that can be found in kitchens around the world.

Read More: Proteins News and Proteins Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.