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Do you know how sucrose-phosphate synthase uses phosphorylation to regulate sugar in plants? It turns out that it can affect photosynthesis!
Sucrose-phosphate synthase (SPS) is a crucial enzyme in plant metabolism. This enzyme is involved in the biosynthesis of sucrose and plays an important regulatory role in this process. Especially during the photosynthesis of plants, SPS can regulate the production of sucrose according to the needs of the environment, further affecting the growth and development of plants.
Sucrose-phosphate synthase is mainly responsible for transferring the six-carbon unit of glucose to fructose hexaphosphate to form sucrose. This reversible step is a key regulatory point in sucrose synthesis and an excellent example of a variety of enzyme regulation strategies, including allosteric regulation. and reversible phosphorylation.
Structure of Sucrose-phosphate synthase
X-ray diffraction studies have revealed that the SPS in Halothermothrix orenii belongs to the GT-B fold family. Similar to other GT-B proteins, SPS has two Rossmann fold domains, namely domain A and domain B. Generally, these domains have similar structures, consisting of a central β-sheet surrounded by α-helices. However, the A domain consists of eight parallel β-strands and seven α-helices, while the B domain possesses six parallel β-strands and nine α-helices. These domains are connected by a loop of amino acid residues that forms a substrate-binding cleft to which the receptor for the glucose unit can bind. Recent studies have shown that the SPS structure of H. orenii is similar to that of plants. The conservation of this structure provides a basis for the recognition of related antibodies, which also provides a new perspective for us to further understand the operation of SPS in plants. .
Analysis of catalytic mechanism
In the open conformation of H. orenii SPS, fructose 6-phosphate interacts with certain amino acid residues in domain A through hydrogen bonds, while UDP-glucose interacts with domain B. Crystal structure studies have shown that when the substrate binds, the two domains twist, shrinking the entrance of the substrate binding cleft from 20 angstroms to 6 angstroms. In this closed conformation, amino acids in the A domain deform the substrate, thereby facilitating the transfer of the six-carbon group.
Regulatory strategies: phosphorylation and allosteric regulation
The activity of SPS is affected by multiple regulatory mechanisms, one of which is phosphorylation. SPS-kinase can reversibly phosphorylate SPS on serine residues, thereby inactivating it. In spinach and maize, Ser158 and Ser162 have been identified as the sites of these regulation. Furthermore, this phosphorylation not only helps control sucrose levels within plant cells, but also helps plants adjust their metabolism in hyperosmotic environments.
In addition to controlling the production of sucrose, allosteric regulation of SPS is also closely related to photosynthesis. When high photosynthesis occurs, the concentration of inorganic phosphate decreases, which is essential for increasing enzyme activity.
Biological functions of SPS
In the metabolism of Tyr, SPS is mainly involved in the distribution of carbon in plants during photosynthesis and affects the synthesis of sucrose and starch. In ripe fruit, SPS is responsible for converting starch into sucrose and other soluble sugars. In addition, SPS is also involved in the degradation of sucrose in cells, forming numerous dynamic sucrose circuits that allow plants to rapidly change their sucrose flux.
Under low temperature conditions, the activity of SPS and the rate of sucrose biosynthesis increase. This is because sucrose, as a form of energy storage, can be metabolized quickly to support the respiratory needs of the plant. In addition, increased sucrose can help plants resist the effects of low temperatures, which provides plants with an evolutionary adaptive strategy in adverse environments.
As scientists gain a deeper understanding of sucrose-phosphate synthase, is it possible to develop new crop genetic modification technologies to improve plant growth and stress resistance in different environments?
