ACADEMIC RESEARCH • 學術研究 2023 UMAGAZINE 27 • 澳大新語 61 RhsP: The Weapon of Vibrio Parahaemolyticus Vibrio parahaemolyticus is a common bacterium found in coastal waters and seafood, especially shellfish such as scallops, oysters, and clams. The bacterium is most active in the summer and autumn months. It can enter the human intestine through the consumption of seafood or contact with seawater, where it multiplies and attacks neighbouring microorganisms. The intestine harbours a variety of microorganisms, including a wide range of bacteria, which are collectively known as the gut flora. A sudden change in the balance of bacteria within the gut flora can lead to various health complications, such as impaired digestion, a weakened immune system, and an increased risk of chronic diseases. How does V. parahaemolyticus attack other microorganisms after entering the gut? Our analysis of the V. parahaemolyticus genome has identified a protein toxin called RhsP. This protein, with a large structure of 1381 amino acids and a molecular weight of 157 kDa (a non-SI unit of mass used to express molecular mass, especially for large molecules such as proteins), is a polymorphic toxin that can change its structure. As a weapon, RhsP creates an environment that favours the proliferation of V. parahaemolyticus in the intestine, causing inflammation and damage to the intestinal mucosa with symptoms such as diarrhoea and vomiting. Autoproteolysis, Dimerisation, and Attack Our findings have shown that RhsP must first undergo a process known as autoproteolysis, which means breaking itself down into fragments. The fragmented RhsP then stick together in groups of two through a process known as dimerisation, forming RhsP dimers. The dimer favours the release of the C-terminal toxic (RhsPC), which is a nuclease that kills other bacteria in the gut by degrading their DNA. How is this toxin transferred to other microorganisms? Our results show that V. parahaemolyticus delivers the RhsP toxin via its type 6 secretion system (T6SS). This system consists of several proteins that function together as a needle-like structure. For the C-terminal toxin RhsPC to reach its target, it needs to bind to one of the T6SS proteins, called VgrG2. One could compare V. parahaemolyticus to an army, with the T6SS serving as their cannons and the RhsPC toxin as the cannonballs. 「RhsPC -RhsPI毒素–免疫蛋白複合體」的蛋白晶體結構 The crystal structure of the RhsPC-RhsPI toxin-immunity pair 周昶行教授及其研究團隊 Prof William Chao with his research team members
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