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JBC封面：蛋白分泌系統(tǒng)T6SS報(bào)道
點(diǎn)擊次數(shù)：1430 發(fā)布時(shí)間：2013-3-20
近年來(lái)，革蘭陰性細(xì)菌的蛋白質(zhì)分泌系統(tǒng)演變各種不同，加入的是VI分泌系統(tǒng)（T6SS）。zui近，科學(xué)家在銅綠假單胞菌H1-T6SS中蛋白分泌系統(tǒng)的研究證實(shí)了人們以前的假設(shè)。相關(guān)研究于2013年3月15日發(fā)表在JBC雜志封面上。
革蘭陰性細(xì)菌的蛋白質(zhì)分泌系統(tǒng)演變成各種分子的納米機(jī)制。蛋白分泌系統(tǒng)和細(xì)胞膜復(fù)合物相關(guān)，細(xì)胞膜復(fù)合物參與了表面附屬物的包裝和溶質(zhì)運(yùn)輸。他們被歸為各類(lèi)，zui近新加入的是VI分泌系統(tǒng)（T6SS）。T6SS分泌系統(tǒng)和噬菌體尾部相似，可驅(qū)動(dòng)DNA注入細(xì)菌中。
封面圖中：你看出來(lái)T6SS 組裝成的尾管式和齒輪結(jié)構(gòu)了么？是不是和噬菌體尾部結(jié)構(gòu)相似呢？
Hcp蛋白和T4噬菌體尾管蛋白gp19相關(guān)，而VgrG蛋白結(jié)構(gòu)類(lèi)似噬菌體的gp27/gp5穿刺裝置。噬菌體尾鞘由gp18組成，當(dāng)其收縮后， 噬菌體尾管和尖鋒穿過(guò)細(xì)菌套膜。有人假設(shè)霍亂弧菌中VIPA和VIPB組裝成鞘狀結(jié)構(gòu)。
zui近，MRC中心的研究人員發(fā)現(xiàn)，銅綠假單胞菌H1-T6SS中HsiB1和HsiC1 組裝成小管，這也證實(shí)了以前的數(shù)據(jù)。這些小管來(lái)自鈍齒輪狀結(jié)構(gòu)的堆疊，主要特點(diǎn)是12倍對(duì)稱(chēng)結(jié)構(gòu)。齒輪的內(nèi)部直徑是100埃，這大的足夠容納一個(gè)Hcp管，因?yàn)镠cp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(gè)穩(wěn)定的復(fù)合物，但是HsiC1的C末端是管狀結(jié)構(gòu)組成的必要因素。生物信息學(xué)分析表明，HsiC1和其C末端區(qū)域的gp18類(lèi)似蛋白有一定的相似性。
總之，此項(xiàng)研究為T(mén)S6蛋白分泌系統(tǒng)結(jié)構(gòu)和機(jī)制提供了更深入的了解，同時(shí)也顯示了一個(gè)噬菌體鞘狀結(jié)構(gòu)極有可能是在所有T6SSs中是個(gè)保守的元素。
生物信息學(xué)分析表明，HsiC1顯示gp18蛋白-樣蛋白在其C-末端區(qū)的相似之處。總之，我們提供了進(jìn)一步的T6SS并顯示，一個(gè)噬菌體sheathlike的結(jié)構(gòu)很可能是一個(gè)保守的元素在所有T6SSs的結(jié)構(gòu)和機(jī)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.