Forthcoming Events

16.12.2021 - 21.12.2021, Honolulu, Hawaii, USA
01.06.2022 - 30.06.2022, Grindelwald, Switzerland
27.06.2022 - 29.06.2022, University College London, UK

News

Nobel Prize in Chemistry awarded to RESOLV Member Benjamin List- for the development of asymmetric organocatalysis
NCCR MUST at Scientifica 2021- Lightning, organic solar cells, and virtual molecules
#NCCRWomen- NCCR MUST celebrates 50 years women’s right to vote in Switzerland
Kick-Off dynaMENT Mentoring for Women in Natural Sciences- with Ursula Keller as plenary speaker
Four new scientific highlights- by MUST PIs Chergui / Milne / Beaud / Staub, by Wolf / Röthlisberger, by Wörner, and Keller
Photon Science Roadmap- for Research Infrastructures 2025-2028 by the Swiss Photon Community
Proof of concept ERC Grant for Ursula Keller Dual-comb laser driven terahertz spectrometer for industrial sensing (DC-THz)
Majed Chergui - elected to the European Academy of Sciences
Ruth Signorell - elected to the European Academy of Sciences
Farewell and Welcome!Chris Milne leaves for the European XFEL, Camila Bacellar takes over

Majed Chergui: Tryptophan-to-heme electron transfer in ferrous myoglobins

April 20, 2015
 

Electron transfer challenges fluorescence resonance analysis 

(From EPFL News)— FRET is often used with the amino acid tryptophan, which has the added advantage of being intrinsically fluorescent. For FRET, the protein to be studied is modified to contain an acceptor molecule at the right position. When the protein changes its 3D structure, tryptophan interacts with the acceptor molecule, and transfers energy to it. The result is a decrease in tryptophan’s fluorescence emission, which can be linked proportionally to tryptophan’s distance from the acceptor molecule. Since the protein’s 3D structure is already known, FRET can tell us a lot about how it has changed.

But there are problems. The lab of Majed Chergui at EPFL has now shown conclusively that FRET readouts can be skewed by the transfer of electrons from tryptophans within proteins. The work builds on a previous paper published in Science (2013) on ferric myoglobins, the protein in our blood that carries oxygen within muscles. In that study, Chergui’s team showed that tryptophan in myoglobin naturally transferred electrons to the protein’s oxygen-binding molecule, which is called “heme”. Because electron transfer also causes a decay in tryptophan’s fluorescence, it can be mistaken as a positive signal, raising the question as to whether this was also the case in other proteins.

In the study discussed here, Chergui’s lab looked at a more biologically relevant class of heme proteins, the ferrous myoglobins, which carry oxygen to muscles. The scientists studied them in their physiological state to see if tryptophan transferred electron to the myoglobin’s oxygen-binding heme molecule. However, they had to work with the extremely short timeframes in which electron transfer takes place. To overcome this obstacle, the scientists developed a new, and, so far, unique spectroscopic tool, called “ultrafast UV two-dimensional spectroscopy”.

The study confirmed that electron transfer indeed takes place between tryptophan and the heme molecule, producing an ionic form of the latter that matched theoretical predictions. In addition, their study demonstrated that electron transfer from tryptophan actually occurs more frequently than previously thought. Consequently, the systematic use of tryptophan fluorescence in FRET studies is called into question. “This discovery really creates problems for studies based on FRET analysis,” says Majed Chergui. “If tryptophan transfers electrons in the tested protein, this could give out false readings that can be mistaken for conformational changes of proteins.”



Monni, R., Al Haddad, A., van Mourik, F., Auböck, G., and Chergui, M. (2015) Tryptophan-to-heme electron transfer in ferrous myoglobins. Proc Natl Acad Sci USA (10.1073/pnas.1423186112)

Picked up by Phys.Org and Science.Daily

back <<
NCCR MUST Office : ETHZ IQE/ULP-HPT H3 | Auguste-Piccard-Hof 1 | 8093 Zurich | E-Mail | +41 44 633 36 02
The National Centres of Competence in Research (NCCR) are a research instrument of the Swiss National Science Foundation
FNSNF