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Structural and functional analysis of violaxanthin de-epoxidase

Guo, Kuo LU (2013) KEMT30 20122
Department of Chemistry
Abstract
Non photochemical quenching (NPQ) is an important way for plants to protect themselves from photooxidative damage. In higher plants, the major and most rapid part of NPQ is qE, which is controlled by the Violaxanthin de-epoxidase (VDE) and zeaxanthin epoxidase (ZE). VDE converts Violaxanthin (Vx) to Antheraxanthin (Ax), and then to Zeaxanthin (Zx). Several experiments were carried through to analyze functional and structural properties of VDE. All the 13 Cysteines(Cys) in VDE were mutated to Serine (Ser) to detect the Cys that contribute to VDE activity. 12 mutations were found with decreased VDE activity. The function of the region between the N-terminal domain and the lipocalin domain was investigated by expression of the peptide before... (More)
Non photochemical quenching (NPQ) is an important way for plants to protect themselves from photooxidative damage. In higher plants, the major and most rapid part of NPQ is qE, which is controlled by the Violaxanthin de-epoxidase (VDE) and zeaxanthin epoxidase (ZE). VDE converts Violaxanthin (Vx) to Antheraxanthin (Ax), and then to Zeaxanthin (Zx). Several experiments were carried through to analyze functional and structural properties of VDE. All the 13 Cysteines(Cys) in VDE were mutated to Serine (Ser) to detect the Cys that contribute to VDE activity. 12 mutations were found with decreased VDE activity. The function of the region between the N-terminal domain and the lipocalin domain was investigated by expression of the peptide before and after the linker region in different lengths combination and followed activity measurement. The results showed that the two independent domains lost majority of activity and N-terminal part of linker region was more important for activity. An experiment was set up to analyze the function of C-terminal by measuring the activity of VDE after cleaving different length of C-terminal. The result showed different degrees of activity loss that was caused by removal of different lengths of the C-terminal. A number of experiments suggests that VDE acts as a dimer that is formed at low pH. These experiments will contribute to further research of the function and structure of VDE. (Less)
Abstract
Popular Science Summary
There is a saying that the sun supports the life living on earth. In general, the sunlight supports plants living, and plants become the base of almost all forms of ecosystems. A reaction called photosynthesis exists in all kinds of plants and is the foundation of usage of sunlight energy. In the photosynthesis process, energy in the sunlight converted into the energy stored in plants, the latter is used in various kinds of biochemical reactions. And during photosynthesis, oxygen is released into the environment and supports the metabolism of all living things. In the photosynthesis process, sunlight energy is gathered by a complex called light harvesting system, and excites chlorophyll, a molecule absorbs light.... (More)
Popular Science Summary
There is a saying that the sun supports the life living on earth. In general, the sunlight supports plants living, and plants become the base of almost all forms of ecosystems. A reaction called photosynthesis exists in all kinds of plants and is the foundation of usage of sunlight energy. In the photosynthesis process, energy in the sunlight converted into the energy stored in plants, the latter is used in various kinds of biochemical reactions. And during photosynthesis, oxygen is released into the environment and supports the metabolism of all living things. In the photosynthesis process, sunlight energy is gathered by a complex called light harvesting system, and excites chlorophyll, a molecule absorbs light. The excited chlorophyll continues to transfer the energy to the following photochemical reactions. In nature, the intensity of the sunlight is changing all the time. Sometimes, plants receive more sunlight energy than they need for the biochemical reactions in photosynthesis, that means not all excited chlorophyll are in use. And excited chlorophyll will dissipate its energy and return to the ground-energy state. The release of energy can form reactive oxygen species, a molecule that is harmful to plants cells. To prevent the formation of oxidative species, plants have evolved some other ways to release the energy in the excited chlorophyll. One typical way of de-excitation of excited chlorophyll is called non-photochemical quenching; it dissipates the energy into heat. Our research is mainly about an enzyme which is important to the major component of the non-photochemical quenching in higher plants. The enzyme is called violaxanthin de-epoxidase (VDE). VDE converts violaxanthin (a chain-structure pigment which contains two epoxy groups) to zeaxanthin (a chain-structure pigment without the two epoxy groups). And zeaxanthin is believed to quench the excited chlorophyll. Our research of VDE is to investigate the structure and function of VDE by using molecular and biochemistry methods. We produce different parts of the VDE molecule and we change cysteines (one kind of amino acid which can form covalent bond to each other) in VDE into another amino acid. We measure the activity of the protein we produced. We found that cysteines are important for VDE activity. Another discovery of ours is that the VDE molecule gives its activity only when two VDE molecules contact to each other in low pH, and this contact is influenced by the end part of VDE. We also found that VDE consists of two independent functional parts; each part can form its own structure independently. We believe our discoveries may contribute to the further functional and structural research of VDE. (Less)
Please use this url to cite or link to this publication:
author
Guo, Kuo LU
supervisor
organization
course
KEMT30 20122
year
type
H2 - Master's Degree (Two Years)
subject
keywords
Proteinvetenskap, Protein Science
language
English
id
3920710
date added to LUP
2013-07-22 15:50:46
date last changed
2013-07-22 15:50:46
@misc{3920710,
  abstract     = {Popular Science Summary
There is a saying that the sun supports the life living on earth. In general, the sunlight supports plants living, and plants become the base of almost all forms of ecosystems. A reaction called photosynthesis exists in all kinds of plants and is the foundation of usage of sunlight energy. In the photosynthesis process, energy in the sunlight converted into the energy stored in plants, the latter is used in various kinds of biochemical reactions. And during photosynthesis, oxygen is released into the environment and supports the metabolism of all living things. In the photosynthesis process, sunlight energy is gathered by a complex called light harvesting system, and excites chlorophyll, a molecule absorbs light. The excited chlorophyll continues to transfer the energy to the following photochemical reactions. In nature, the intensity of the sunlight is changing all the time. Sometimes, plants receive more sunlight energy than they need for the biochemical reactions in photosynthesis, that means not all excited chlorophyll are in use. And excited chlorophyll will dissipate its energy and return to the ground-energy state. The release of energy can form reactive oxygen species, a molecule that is harmful to plants cells. To prevent the formation of oxidative species, plants have evolved some other ways to release the energy in the excited chlorophyll. One typical way of de-excitation of excited chlorophyll is called non-photochemical quenching; it dissipates the energy into heat. Our research is mainly about an enzyme which is important to the major component of the non-photochemical quenching in higher plants. The enzyme is called violaxanthin de-epoxidase (VDE). VDE converts violaxanthin (a chain-structure pigment which contains two epoxy groups) to zeaxanthin (a chain-structure pigment without the two epoxy groups). And zeaxanthin is believed to quench the excited chlorophyll. Our research of VDE is to investigate the structure and function of VDE by using molecular and biochemistry methods. We produce different parts of the VDE molecule and we change cysteines (one kind of amino acid which can form covalent bond to each other) in VDE into another amino acid. We measure the activity of the protein we produced. We found that cysteines are important for VDE activity. Another discovery of ours is that the VDE molecule gives its activity only when two VDE molecules contact to each other in low pH, and this contact is influenced by the end part of VDE. We also found that VDE consists of two independent functional parts; each part can form its own structure independently. We believe our discoveries may contribute to the further functional and structural research of VDE.},
  author       = {Guo, Kuo},
  keyword      = {Proteinvetenskap,Protein Science},
  language     = {eng},
  note         = {Student Paper},
  title        = {Structural and functional analysis of violaxanthin de-epoxidase},
  year         = {2013},
}