Unmatched fineness refreshes new molecular machines for "photosynthesis"

Photosynthesis is the most important foundation of
life on Earth.
Here, plants and single-celled algae harness the energy of sunlight and convert this energy into sugar and biomass
.
In the process, oxygen is released
.
Plant biotechnologists and structural biologists from the Universities of Münster (Germany) and Stockholm (Sweden) have elucidated the structure of a new protein complex that catalyzes the energy conversion process
in photosynthesis.
This protein complex is photosystem I, which is called a single-protein complex (monomer)
in plants.
The research team, led by Prof.
Michael Hippler from the University of Münster and Prof.
Alexey Amunts from Stockholm University, has now shown for the first time that two photosystem I monomers in plants can be joined together as dimers, and they describe the molecular structure
of this new molecular machine.
The findings, published in the journal Nature Plants, provide molecular insight into the process of photosynthesis with a degree of precision hitherto unparalleled
.
They could help to make more efficient use of the reducing power of photosystem I in the future, for example by producing hydrogen as an energy source
.

We know that there are two photosynthetic complexes described in biology textbooks as photosynthetic systems, called photosystem I and photosystem II, that work best
with different wavelengths of light.
Light energy is absorbed into photosystems I and II, allowing electrons to be transported within the molecular "photosynthetic machine," which propels the conversion of light energy into chemical energy
.
In this process, electrons from photosystem I are transported to the protein ferrodoldin
.
In green algae, ferroproteins can transfer electrons produced during photosynthesis to an enzyme called hydrogenase, which then produces hydrogen molecules
.
Therefore, this molecular hydrogen is produced through the input of light energy, which means that it is renewable and may be a future energy source
.
The researchers asked: "How is hydrogen produced by photosynthesis related to the structural dynamics of monomer and dimer photosystem I?"

Detailed results:

Chlamydomonas reinhardtii's photosystem I homodimer consists of 40 protein subunits and 118 transmembrane helices, providing structure
for 568 photosynthetic pigments.
Using cryo-electron microscopy, the researchers found that the deletion of PsaH and Lhca2 subunits led to head-to-head orientation
of the monomeric photosystem I (PSI) and its associated light-collecting protein (LHCI).
The light-collecting protein Lhca9 is a key element
in providing this dimerization.

In this study, the researchers defined the most accurate available PSI-LHCI model with a resolution of 2.
3 Ångström (1Å corresponds to ten-millionths of a millimeter), including the flexibly bound electron transmitter plasticyanin, which they assigned the correct identification and orientation of all pigments, and 621 water molecules
that affect the energy transport pathway.
Associated with the loss of the second gene (pgr5), the downregulation of the gene-induced subunit Lhca2 leads to a very efficient production
of hydrogen in the double mutant.
As Michael Hippler puts it: "The depletion of Lhca2 promotes the formation of PSI dimers, so we think hydrogenases may be more inclined to target photosynthetic electrons from PSI dimers, as we proposed in our earlier work
.
" The structure of the PSI dimer allows us to make targeted genetic modifications to test the hypothesis
of improved hydrogen production through the PSI dimer.
”