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JBC封面：蛋白分泌系統T6SS報道
點擊次數：1516 發布時間：2013-3-20
近年來，革蘭陰性細菌的蛋白質分泌系統演變各種不同，加入的是VI分泌系統（T6SS）。zui近，科學家在銅綠假單胞菌H1-T6SS中蛋白分泌系統的研究證實了人們以前的假設。相關研究于2013年3月15日發表在JBC雜志封面上。
革蘭陰性細菌的蛋白質分泌系統演變成各種分子的納米機制。蛋白分泌系統和細胞膜復合物相關，細胞膜復合物參與了表面附屬物的包裝和溶質運輸。他們被歸為各類，zui近新加入的是VI分泌系統（T6SS）。T6SS分泌系統和噬菌體尾部相似，可驅動DNA注入細菌中。
封面圖中：你看出來T6SS 組裝成的尾管式和齒輪結構了么？是不是和噬菌體尾部結構相似呢？
Hcp蛋白和T4噬菌體尾管蛋白gp19相關，而VgrG蛋白結構類似噬菌體的gp27/gp5穿刺裝置。噬菌體尾鞘由gp18組成，當其收縮后， 噬菌體尾管和尖鋒穿過細菌套膜。有人假設霍亂弧菌中VIPA和VIPB組裝成鞘狀結構。
zui近，MRC中心的研究人員發現，銅綠假單胞菌H1-T6SS中HsiB1和HsiC1 組裝成小管，這也證實了以前的數據。這些小管來自鈍齒輪狀結構的堆疊，主要特點是12倍對稱結構。齒輪的內部直徑是100埃，這大的足夠容納一個Hcp管，因為Hcp管的外部直徑是85埃。
HsiC1的N末端212位氨基酸殘基足夠與HsiB1形成一個穩定的復合物，但是HsiC1的C末端是管狀結構組成的必要因素。生物信息學分析表明，HsiC1和其C末端區域的gp18類似蛋白有一定的相似性。
總之，此項研究為TS6蛋白分泌系統結構和機制提供了更深入的了解，同時也顯示了一個噬菌體鞘狀結構極有可能是在所有T6SSs中是個保守的元素。
生物信息學分析表明，HsiC1顯示gp18蛋白-樣蛋白在其C-末端區的相似之處。總之，我們提供了進一步的T6SS并顯示，一個噬菌體sheathlike的結構很可能是一個保守的元素在所有T6SSs的結構和機制的深入了解。
原文摘要：
The HsiB1C1 （TssB-TssC） Complex of thePseudomonas aeruginosa Type VI Secretion System Forms a Bacteriophage Tail Sheathlike Structure
Protein secretion systems in Gram-negative bacteria evolved into a variety of molecular nanomachines. They are related to cell envelope complexes, which are involved in assembly of surface appendages or transport of solutes. They are classified as types, the most recent addition being the type VI secretion system （T6SS）. The T6SS displays similarities to bacteriophage tail, which drives DNA injection into bacteria. The Hcp protein is related to the T4 bacteriophage tail tube protein gp19, whereas VgrG proteins structurally resemble the gp27/gp5 puncturing device of the phage. The tube and spike of the phage are pushed through the bacterial envelope upon contraction of a tail sheath composed of gp18. In Vibrio cholerae it was proposed that VipA and VipB assemble into a tail sheathlike structure. Here we confirm these previous data by showing that HsiB1 and HsiC1 of the Pseudomonas aeruginosa H1-T6SS assemble into tubules resulting from stacking of cogwheel-like structures showing predominantly 12-fold symmetry. The internal diameter of the cogwheels is ∼100 Å, which is large enough to accommodate an Hcp tube whose external diameter has been reported to be 85 Å. The N-terminal 212 residues of HsiC1 are sufficient to form a stable complex with HsiB1, but the C terminus of HsiC1 is essential for the formation of the tubelike structure. Bioinformatics analysis suggests that HsiC1 displays similarities to gp18-like proteins in its C-terminal region. In conclusion, we provide further structural and mechanistic insights into the T6SS and show that a phage sheathlike structure is likely to be a conserved element across all T6SSs.