Unraveling the initial molecular events of respiration

Date:
August 18, 2020
Source:
Ecole Polytechnique Fe'de'rale de Lausanne
Summary:
Physicists from Switzerland, Japan and Germany have unveiled the
mechanism by which the first event of respiration takes place in
heme proteins.



FULL STORY ========================================================================== Respiration is a fundamental process of all living things, allowing them
to produce energy, stay healthy, and survive. In cells, respiration
involves what are known as "respiratory proteins," e.g. hemoglobin in
the blood and myoglobin in muscles.


========================================================================== Respiratory proteins work by binding and releasing small molecules
like oxygen, carbon monoxide etc., called ligands. They do this through
their "active center," which in many respiratory proteins is a chemical structure called heme porphyrin.

Binding and releasing small molecules causes changes in the heme's
molecular and electronic structure. Such a change is the transition from
a planar low spin ligated porphyrin form to a domed high spin un-ligated
form and vice- versa. This shift is a key step for respiration, ultimately switching hemoglobin between a "relaxed" and "tense" conformation.

Electrons spin around atoms, but also spin around themselves, and can
cross over from one spin state to another. The debate about the transition
from low- spin planar to a high-spin domed heme has been dominated by
two schools of thought: the process is either by thermal relaxation or
by a cascade among electron spin states.

Now, a team of scientists led by Majed Chergui at EPFL's School of Basic Sciences have solved the debate. The researchers detached the small
molecule from the heme using short, energizing laser pulses. They then
used another short, hard X-ray pulse from an X-ray free-electron laser
to induce X-ray emission (XES), a very sensitive fingerprint of the spin
state of molecules, which monitored the heme's changes as a function of
time. They could thus determine that the passage from planar to domed
and back is caused by a cascade among spin states.

The study was carried out on nitrosyl-myoglobin, which is myoglobin that
has bound a nitric oxide molecule. Nitrosyl-myoglobin plays a crucial role
in neurotransmission, regulation of vasodilatation, platelet aggregation,
and immune responses.

"The conclusions of our work apply to all heme proteins," says
Chergui. "In particular to hemoglobin in its uptake and release of oxygen
when we breathe.

Although this takes place at the thermal temperatures of the body,
breathing is governed by electronic changes in the heme."

========================================================================== Story Source: Materials provided by
Ecole_Polytechnique_Fe'de'rale_de_Lausanne. Original written by Majed
Chergui, Nik Papageorgiou. Note: Content may be edited for style and
length.


========================================================================== Journal Reference:
1. Dominik Kinschel, Camila Bacellar, Oliviero Cannelli, Boris Sorokin,
Tetsuo Katayama, Giulia F. Mancini, Je're'my R. Rouxel, Yuki Obara,
Junichi Nishitani, Hironori Ito, Terumasa Ito, Naoya Kurahashi,
Chika Higashimura, Shotaro Kudo, Theo Keane, Frederico A. Lima,
Wojciech Gawelda, Peter Zalden, Sebastian Schulz, James M. Budarz,
Dmitry Khakhulin, Andreas Galler, Christian Bressler, Christopher
J. Milne, Thomas Penfold, Makina Yabashi, Toshinori Suzuki, Kazuhiko
Misawa, Majed Chergui. Femtosecond X-ray emission study of the
spin cross-over dynamics in haem proteins. Nature Communications,
2020; 11 (1) DOI: 10.1038/ s41467-020-17923-w ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/08/200818094015.htm

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