RESEARCH: PHOTOSYNTHESIS
FOLDING PROJECT #19328 PROFILE

This project relates to how plants adjust their photosynthesis in different light conditions. They use a special cycle with pigments called carotenoids to absorb excess light energy and protect themselves from damage. A key enzyme, VDE, is activated by acidic conditions and changes shape to work better. This lets the plant efficiently handle bright light.

Note: This TLDR is a simplication and may not be 100% accurate.

To adapt to shifting lighting conditions, plants modify their photosynthetic activity.

The xanthophyll cycle, in which the carotenoid violaxanthin is transformed into zeaxanthin in strong light, plays a key role in controlling photosynthesis.

This process activates the disposal of excess absorbed energy as heat and the scavenging of reactive oxygen species.

When photosynthetic electron transport exceeds the capacity of assimilatory reactions, violaxanthin deepoxidase (VDE), the enzyme responsible for zeaxanthin synthesis, is activated by the acidification of the thylakoid lumen.

At neutral pH, VDE is a soluble and inactive enzyme, but at acidic pH, it attaches to the thylakoid membrane where it binds its substrate.

Ascorbate is used by VDE as a cosubstrate as well, and its pH-dependent Km may indicate a preference for ascorbic acid.

At neutral and acidic pH, we established the structures of the central lipocalin domain of VDE (VDEcd).

VDEcd is monomeric and has its active site blocked by a lipocalin barrel at neutral pH.

The barrel unwinds and the enzyme emerges as a dimer during acidification.

The two violaxanthin beta-ionone rings may be deep oxidized simultaneously in two channels that connect the two active sites of the dimer, giving VDE an ideal example of an asymmetric enzyme's adaptation to its symmetric substrate.

---

photosynthesis

The process by which plants convert light energy into chemical energy.

Photosynthesis is how plants use sunlight, water, and carbon dioxide to make their own food (sugar) and release oxygen. It's essential for life on Earth because it provides the oxygen we breathe and the basis of most food chains.

---

xanthophyll cycle

A series of chemical reactions in plants that regulates light absorption and protects against photodamage.

The xanthophyll cycle involves pigments called carotenoids, which help plants manage excess light energy. When there's too much light, these pigments convert between different forms to dissipate energy as heat and prevent damage.

---

violaxanthin

A type of carotenoid pigment involved in the xanthophyll cycle.

Violaxanthin is a yellow pigment found in plants that plays a role in protecting them from excess light. It can be converted into other pigments as needed to dissipate energy and prevent damage.

---

zeaxanthin

A type of carotenoid pigment involved in the xanthophyll cycle.

Zeaxanthin is another yellow pigment found in plants that helps protect them from excess light. It's produced from violaxanthin when there's too much light and helps dissipate energy.

---

violaxanthin deepoxidase (VDE)

Violaxanthin deepoxidase (VDE) is an enzyme that catalyzes the conversion of violaxanthin to zeaxanthin.

VDE is a key player in the xanthophyll cycle. It's activated when light levels are high and helps convert violaxanthin into zeaxanthin, protecting plants from damage.

---

ascorbate

A water-soluble vitamin also known as ascorbic acid.

Ascorbate is a powerful antioxidant that helps protect cells from damage. It's important for many bodily functions and can be found in fruits and vegetables.

---

lipocalin

A family of small proteins that bind and transport various molecules.

Lipocalins are found in many organisms and play diverse roles. They can bind to lipids, hormones, vitamins, and other substances, transporting them within cells or between tissues.

---

dimer

Two identical or similar molecules joined together.

A dimer is formed when two separate units come together. This can happen with many types of molecules, including proteins, DNA, and RNA.