RESEARCH: VIOLAXANTHIN-DEEPOXIDASE-STRUCTURE
FOLDING PROJECT #19332 PROFILE

Plants change how they make food (photosynthesis) when light levels change. A process called the xanthophyll cycle helps with this, using an enzyme called VDE to turn violaxanthin into zeaxanthin in bright light. This protects plants from excess energy and damage. The project relates to how VDE works at different pH levels, showing that it changes shape and becomes more active in acidic conditions.

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 (glucose) and release oxygen as a byproduct. This process is essential for life on Earth as it provides the oxygen we breathe and the basis of most food chains.

carotenoid

A group of pigments that give plants their yellow, orange, and red colors.

Carotenoids are a diverse group of natural pigments found in plants, algae, and some bacteria. They absorb light in the blue and green regions of the spectrum, reflecting yellows, oranges, and reds. Besides providing color, carotenoids play important roles in photosynthesis and protect plants from damage caused by excess light.

violaxanthin

A type of carotenoid that is involved in the xanthophyll cycle.

Violaxanthin is a yellow pigment found in plants. It plays a crucial role in the xanthophyll cycle, a process that helps plants protect themselves from damage caused by excess light. Violaxanthin can be converted into zeaxanthin under high light conditions, which dissipates excess energy as heat.

zeaxanthin

A type of carotenoid that is involved in the xanthophyll cycle.

Zeaxanthin is a yellow pigment found in plants. It plays a crucial role in the xanthophyll cycle, a process that helps plants protect themselves from damage caused by excess light. Zeaxanthin absorbs excess light energy and dissipates it as heat, protecting the plant's photosynthetic machinery.

violaxanthin deepoxidase (VDE)

Enzyme responsible for zeaxanthin synthesis.

VDE is an enzyme that catalyzes the conversion of violaxanthin to zeaxanthin in plants. This process is essential for regulating photosynthesis and protecting plants from damage caused by excess light.

thylakoid lumen

The space inside the thylakoids of chloroplasts.

The thylakoid lumen is a specialized compartment within chloroplasts, the organelles responsible for photosynthesis in plants. It plays a crucial role in creating an electrochemical gradient that drives ATP synthesis, a key process in energy production.