盡管細菌用其產(chǎn)生的蛋白質(zhì)量的1/3來構(gòu)建其外膜,，但是目前研究者并不清楚細菌的外膜S層結(jié)構(gòu)和具體功能。來自英國,、法國和比利時的研究者對土壤細菌嗜熱脂肪土芽孢桿菌的完整S層進行成像至單一的原子規(guī)模,，他們揭示了保護層的蛋白質(zhì)可以像中世紀騎士的盔甲一樣互相掛住。研究者Stefan Howorka解釋道,，盡管研究者發(fā)現(xiàn)了很多的細菌,，可是對于蛋白質(zhì)外套仍然知之甚少。運用先進的成像技術(shù),，研究者首次揭開了細菌S層的具體結(jié)構(gòu),，S層的蛋白質(zhì)是以一種鏈的方式進行裝配的。相關(guān)研究成果刊登在了近日的國際雜志Nature上,。
這種鏈甲外套結(jié)構(gòu)（chainmail coat）不僅僅支撐了細菌的形狀,，而且保護細菌遠離環(huán)境危害。而且這種外套結(jié)構(gòu)對于某些致病菌感染細胞異常重要，可以幫助細菌依附在人類或動物細胞的表面,。有些致病菌的外套結(jié)構(gòu)帶有網(wǎng)格蛋白,，可以逃過免疫細胞的防御。
研究者目前可以獲得某種細菌S層的結(jié)構(gòu),，而且它們表示在未來不久也可以揭示其它物種的蛋白質(zhì)外套結(jié)構(gòu),。S層外套的顯著結(jié)構(gòu)可以作為極有希望的疫苗載體，開發(fā)并且理解這些外套的能力,，而后研究者破壞其功能,，通過將致病菌的少量蛋白和無害的S層進行混合就有可能構(gòu)建出混合疫苗。（生物谷Bioon.com）
編譯自：Revealing bacterial chainmail structure
編譯者：T.Shen
doi:10.1038/nature11155
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SbsB structure and lattice reconstruction unveil Ca2+ triggered S-layer assembly
Ekaterina Baranova,1, 2 Rémi Fronzes,3, 4 Abel Garcia-Pino,2 Nani Van Gerven,1, 2 David Papapostolou,5 Gérard Péhau-Arnaudet,4 Els Pardon,2 Jan Steyaert,2 Stefan Howorka5 & Han Remaut1, 2
S-layers are regular two-dimensional semipermeable protein layers that constitute a major cell-wall component in archaea and many bacteria1, 2, 3. The nanoscale repeat structure of the S-layer lattices and their self-assembly from S-layer proteins (SLPs) have sparked interest in their use as patterning and display scaffolds for a range of nano-biotechnological applications4, 5, 6, 7. Despite their biological abundance and the technological interest in them, structural information about SLPs is limited to truncated and assembly-negative proteins8, 9, 10. Here we report the X-ray structure of the SbsB SLP of Geobacillus stearothermophilus PV72/p2 by the use of nanobody-aided crystallization. SbsB consists of a seven-domain protein, formed by an amino-terminal cell-wall attachment domain and six consecutive immunoglobulin-like domains, that organize into a ϕ-shaped disk-like monomeric crystallization unit stabilized by interdomain Ca2+ ion coordination. A Ca2+-dependent switch to the condensed SbsB quaternary structure pre-positions intermolecular contact zones and renders the protein competent for S-layer assembly. On the basis of crystal packing, chemical crosslinking data and cryo-electron microscopy projections, we present a model for the molecular organization of this SLP into a porous protein sheet inside the S-layer. The SbsB lattice represents a previously undescribed structural model for protein assemblies and may advance our understanding of SLP physiology and self-assembly, as well as the rational design of engineered higher-order structures for biotechnology4, 5, 6, 7.
