尽管细菌用其产生的蛋白质量的1/3来构建其外膜,但是目前研究者并不清楚细菌的外膜S层结构和具体功能。来自英国、法国和比利时的研究者对土壤细菌嗜热脂肪土芽孢杆菌的完整S层进行成像至单一的原子规模,他们揭示了保护层的蛋白质可以像中世纪骑士的盔甲一样互相挂住。研究者Stefan Howorka解释道,尽管研究者发现了很多的细菌,可是对于蛋白质外套仍然知之甚少。运用先进的成像技术,研究者首次揭开了细菌S层的具体结构,S层的蛋白质是以一种链的方式进行装配的。相关研究成果刊登在了近日的国际杂志Nature上。
这种链甲外套结构(chainmail coat)不仅仅支撑了细菌的形状,而且保护细菌远离环境危害。而且这种外套结构对于某些致病菌感染细胞异常重要,可以帮助细菌依附在人类或动物细胞的表面。有些致病菌的外套结构带有网格蛋白,可以逃过免疫细胞的防御。
研究者目前可以获得某种细菌S层的结构,而且它们表示在未来不久也可以揭示其它物种的蛋白质外套结构。S层外套的显著结构可以作为极有希望的疫苗载体,开发并且理解这些外套的能力,而后研究者破坏其功能,通过将致病菌的少量蛋白和无害的S层进行混合就有可能构建出混合疫苗。(生物谷Bioon.com)
编译自:Revealing bacterial chainmail structure
编译者: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.