Mutational Analyses Reveal Overall Topology and Functional Regions of NilB, a Bacterial Outer Membrane Protein Required for Host Association in a Model of Animal-Microbe Mutualism
Mutational Analyses Reveal Overall Topology and Functional Regions of NilB, a Bacterial Outer Membrane Protein Required for Host Association in a Model of Animal-Microbe Mutualism
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DOI：
10.1128/jb.06711-11
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发表时间：
2012-04-01
影响因子：
3.2
通讯作者：
Goodrich-Blair, Heidi
中科院分区：
文献类型：
--
作者：
Bhasin, Archna;Chaston, John M.;Goodrich-Blair, Heidi
γ-变形杆菌Xellabdus philophila是一种互惠共生体，定居在线虫Steinernema carpocapsae的肠道中。nilB（nematode intestinal localization）是X.嗜线虫定殖线虫，并预测编码一个完整的外膜β-桶蛋白，但支持这一预测的证据还没有报道。NilB的功能尚不清楚，但当与由nilA和nilC编码的另外两个因子一起表达时，它赋予非同源的Xabridus spp.殖民S的能力。果荚线虫我们提出的证据表明，NilB是一种表面暴露的外膜蛋白，其表达被NilR抑制，并在营养丰富的培养基中生长。生物信息学分析表明，NilB是唯一的特征性成员的一个家庭的蛋白质区分的N-末端区域tetratricopeptide repeats（TPR）和一个保守的C-末端结构域的未知功能（DUF 560）。该家族的成员存在于不同的细菌中，并且在粘膜病原体的基因组中普遍存在。插入和缺失突变分析支持β桶结构模型与N-末端球状结构域，14个跨膜链，和7个细胞外表面环，并揭示了关键作用的球状结构域和表面环6线虫定植。这些突变体的落射荧光显微镜表明，NilB是必要的，在早期阶段的殖民。这些发现是理解NilB功能的重要一步，并且通过扩展，其在粘膜病原体中的同源物。
The gammaproteobacterium Xenorhabdus nematophila is a mutualistic symbiont that colonizes the intestine of the nematode Steinernema carpocapsae. nilB (nematode intestine localization) is essential for X. nematophila colonization of nematodes and is predicted to encode an integral outer membrane beta-barrel protein, but evidence supporting this prediction has not been reported. The function of NilB is not known, but when expressed with two other factors encoded by nilA and nilC, it confers upon noncognate Xenorhabdus spp. the ability to colonize S. carpocapsae nematodes. We present evidence that NilB is a surface-exposed outer membrane protein whose expression is repressed by NilR and growth in nutrient-rich medium. Bioinformatic analyses reveal that NilB is the only characterized member of a family of proteins distinguished by N-terminal region tetratricopeptide repeats (TPR) and a conserved C-terminal domain of unknown function (DUF560). Members of this family occur in diverse bacteria and are prevalent in the genomes of mucosal pathogens. Insertion and deletion mutational analyses support a beta-barrel structure model with an N-terminal globular domain, 14 transmembrane strands, and seven extracellular surface loops and reveal critical roles for the globular domain and surface loop 6 in nematode colonization. Epifluorescence microscopy of these mutants demonstrates that NilB is necessary at early stages of colonization. These findings are an important step in understanding the function of NilB and, by extension, its homologs in mucosal pathogens.