Release Subtitle:
Scientists reveal the exact process behind the upkeep of one of the cellular components where photosynthesis occurs
Release Summary Text:
Photosynthesis is at the core of all life. But what lies at the crux of
photosynthesis? Scientists have long known of the specific components of
the cell where photosynthesis occurs, but the precise mechanisms by
which these components are maintained remain unknown. Now, the
possibility of unprecedented high-resolution visualization using
cryo-electron microscopy has allowed a team of scientists to reveal how
the structural integrity of the site of one half of the photosynthesis
process is maintained.
Full text of release:
“All living beings, including us, depend on photosynthesis,” says Prof.
Wataru Sakamoto of the Institute of Plant Science and Resources at
Okayama University, Japan, as he begins to explain the core concepts
behind a recent breakthrough in understanding plant physiology, which he
was involved in. “Photosynthesis produces the energy needed to sustain
plants and the oxygen we breathe. This reaction occurs in two steps, the
first of which involves capturing light energy and producing oxygen.
This step takes place in a cell organelle in the plant cells called the
chloroplast: specifically, in the membranes of one of its components,
the thylakoid. The thylakoid membrane is unique to oxygen-producing
organisms like plants and cyanobacteria, and its role has been known for
over 200 years. Yet, even today in the technology age, the precise
mechanisms that that shape this structure are unknown to us.”
Now, Prof. Sakamoto and an international team of scientists have
answered part of this question by focusing on a membrane remodeling
protein, called VIPP1, which has been found to be involved in
maintaining the integrity of the thylakoid membrane. Using high
resolution imaging via cryo-electron microscopy, they’ve elucidated the
mechanism by which this protein protects thylakoid membrane integrity.
Their findings are published in the journal Cell.
Speaking of his motivation for being part of this study, Prof. Sakamoto
says, “Chloroplasts in land plants are thought to have been derived from
the endosymbiosis of cyanobacteria in plants 1.5 billion years ago. I
was very fascinated by this during my college years and decided to study
such organelles containing multiple membranes and their own DNA, like
mitochondria and chloroplasts. In my laboratory, I have been working on
VIPP1 since 2006, and have reported several of its important
characteristics.”
In this study, what the scientists observed was remarkable. Three VIPP1
monomers ‘flex and interweave’ in a specific formation to create a
nucleotide binding pocket. Nucleotide binding to specific layers of such
interwoven monomers cause layer stacking that results in basket-like
structures of different symmetries. A part of the monomer is an
amphiphilic—structure containing both water-attracting and
water-repelling portions—helix. Within the basket structure, these
helices are oriented such that their hydrophilic (water-attracting)
portions face the outside of the basket and their hydrophobic
(water-repelling) portions face the inside of the basket. The
hydrophobic portions are also lipid (fat) attracting. Thylakoid
membranes, like most cell membranes, are lipid membranes. The
hydrophobic interior of the basket structure binds to the membrane and
remodels it by increasing its curvature.
In their experiments, when the scientists added mutations to prevent the
hydrophobic surfaces from forming, stress on the membrane from high
intensity light caused the thylakoid membrane to swell up and get
damaged. This damage did not occur in membranes which had access to
VIPP1 oligomers with hydrophobic surfaces.
Dr. Sakamoto explains the importance of these results in the field of
research: “Our study reports that the membrane-remodeling protein VIPP1
plays a critical role in maintaining thylakoid membranes. This protein
appears to share a common structure with ESCRT-III, which is important
in membrane remodeling in humans and yeast, indicating that the
mechanism at play here is a common mechanism regulating membrane
integrity.” Further referring to more tangible potential practical
applications, he says: “Thylakoid is key to photosynthesis.
Understanding its structure in detail can help crop production and thus
food security. For instance, improving thylakoid membrane longevity can
improve crop productivity.” And of course, all things considered, this
finding resolves a long-standing mystery in the biology underlying
photosynthesis.
Release URL:
https://www.eurekalert.org/pub_releases/2021-07/ou-gtt071221.php
Reference:
Title of original paper: Structural basis for VIPP1 oligomerization and maintenance of thylakoid membrane integrity
Journal: Cells
DOI: 10.1016/j.cell.2021.05.011
Contact Person: Wataru Sakamoto
Dr. Wataru Sakamoto is a Professor at the Institute of Plant Science and
Resources, Okayama University, Japan. Dr. Sakamoto leads the Plant
Light Acclimation Research Group. His areas of research include that of
plant physiology, like plastids, thylakoid membranes, pollen etc. He has
an experience over 30 years in this field. His expertise is bolstered
by several publications, including 143 research articles, 14 review
articles, and 3 book chapters, with over 4600 citations.
https://www.okayama-u.ac.jp/eng/research_highlights/index_id138.html
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