A novel membrane protein influencing cell shape and multicellular swarming of Proteus mirabilis
A novel membrane protein influencing cell shape and multicellular swarming of Proteus mirabilis
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DOI：
10.1128/jb.181.7.2008-2016.1999
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发表时间：
1999-04-01
影响因子：
3.2
通讯作者：
Hughes, C
中科院分区：
文献类型：
--
作者：
Hay, NA;Tipper, DJ;Hughes, C
奇异变形杆菌群集的特征是高度伸长的、超鞭毛的群细胞的多细胞筏的协调表面迁移。我们描述了一个转座子突变体，MNS 185，这是无法群集，即使营养细胞保持正常的运动和分化成群细胞的能力。然而，这些细长的细胞是不规则的弯曲，并具有可变的直径，这表明迁移缺陷的结果，这些变形的群细胞无法对齐成多细胞筏。转座子插入到缺乏可识别同源物的228个密码子基因的密码子196处。用于弯曲细胞形态的野生型基因（称为ccmA）的多个拷贝恢复了突变体的群集。预测25-kDa CcmA蛋白跨越内膜两次，其C末端主要结构域存在于细胞质中，通过免疫印迹和免疫金标记切片的电子显微镜检查证实了膜定位。在野生型奇异变形杆菌中鉴定出两种形式的CcmA;它们是全长完整膜CcmA 1和N末端截短的外周膜CcmA 2，两者在群细胞中的浓度都高出约20倍。分化的MNS 185突变体细胞含有两种蛋白质的C-末端截短版本的野生型水平。ccmA无效突变体的细长细胞比MNS 185的那些畸形少，并且能够群集，尽管比野生型更慢。因此，截短的CcmA蛋白可能会干扰正常的形态发生，而野生型蛋白，这不是必不可少的群集，可能会提高迁移，保持高度细长的细胞的线性。与这一观点相一致的是，ccmA基因的过表达导致大肠杆菌和奇异变形杆菌的细胞都变得增大和椭圆形。
Swarming in Proteus mirabilis is characterized by the coordinated surface migration of multicellular rafts of highly elongated, hyperflagellated swarm cells. We describe a transposon mutant, MNS185, that was unable to swarm even though vegetative cells retained normal motility and the ability to differentiate into swarm cells. However, these elongated cells were irregularly curved and had variable diameters, suggesting that the migration defect results from the inability of these deformed swarm cells to align into multicellular rafts. The transposon was inserted at codon 196 of a 228-codon gene that lacks recognizable homologs, Multiple copies of the wild-type gene, called ccmA, for curved cell morphology, restored swarming to the mutant, The 25-kDa CcmA protein is predicted to span the inner membrane twice, with its C-terminal major domain being present in the cytoplasm, Membrane localization was confirmed both by immunoblotting and by electron microscopy of immunogold-labelled sections. Two forms of CcmA were identified for wild-type P. mirabilis; they were full-length integral membrane CcmA1 and N-terminally truncated peripheral membrane CcmA2, both present at approximately 20-fold higher concentrations in swarm cells. Differentiated MNS185 mutant cells contained wild-type levels of the C-terminally truncated versions of both proteins. Elongated cells of a ccmA null mutant were less misshapen than those of MNS185 and were able to swarm, albeit more slowly than wild-type tells. The truncated CcmA proteins may therefore interfere with normal morphogenesis, while the wild-type proteins, which are not essential for swarming, may enhance migration by maintaining the linearity of highly elongated cells. Consistent with this view, overexpression of the ccmA gene caused cells of both Escherichia coli and P. mirabilis to become enlarged and ellipsoidal.