Cava Felipe, de Pedro Miguel A, Schwarz Heinz, Henne Anke, Berenguer José
Centro de Biología Molecular Severo Ochoa, Consejo Superior de Investigaciones Científicas-Universidad Autónoma de Madrid, Campus de Cantoblanco, 28049 Madrid, Spain.
Mol Microbiol. 2004 May;52(3):677-90. doi: 10.1111/j.1365-2958.2004.04011.x.
Electron microscopy of isolated cell walls of the ancient bacterium Thermus thermophilus revealed that most of the peptidoglycan (PG) surface, apart from the septal region, was shielded against specific alphaPG antibodies. On the other hand, an antiserum raised against S-layer-attached cell wall fragments (alphaSAC) bound to most of the surface except for the septal regions. Treatments with alpha-amylase and pronase E made the entire cell wall surface uniformly accessible to alphaPG and severely decreased the binding of alphaSAC. We concluded that a layer of strongly bound secondary cell wall polymers (SCWPs) covers most of the cell wall surface in this ancient bacterium. A preliminary analysis revealed that such SCWPs constitute 14% of the cell wall and are essentially composed of sugars. Enzyme treatments of the cell walls revealed that SCWP was required in vitro for the binding of the S-layer protein through the S-layer homology (SLH) motif. The csaB gene was necessary for the attachment of the S-layer-outer membrane (OM) complex to the cell wall in growing cells of T. thermophilus. In vitro experiments confirmed that cell walls from a csaB mutant bound to the S-layer with a much lower affinity ( approximately 1/10) than that of the wild type. CsaB was found to be required for pyruvylation of components of the SCWP and for immunodetection with alpha-SAC antiserum. Therefore, the S-layer-OM complex of T. thermophilus binds to the cell wall through the SLH motif of the S-layer protein via a strong interaction with a highly immunogenic pyruvylated component of the SCWP. Immuno-cross-reactive compounds were detected with alphaSAC on cell walls of other Thermus spp. and in the phylogenetically related microorganism Deinococcus radiodurans. These results imply that the interaction between the SLH motif and pyruvylated components of the cell wall arose early during bacterial evolution as an ancestral mechanism for anchoring proteins and outer membranes to the cell walls of primitive bacteria.
对嗜热栖热菌这种古老细菌的分离细胞壁进行电子显微镜观察发现，除了隔膜区域外，大部分肽聚糖（PG）表面对特定的αPG抗体具有屏蔽作用。另一方面，针对与S层相连的细胞壁片段产生的抗血清（αSAC）能结合除隔膜区域外的大部分表面。用α淀粉酶和链霉蛋白酶E处理后，整个细胞壁表面对αPG变得均匀可及，同时αSAC的结合力大幅下降。我们得出结论，在这种古老细菌中，一层紧密结合的次生细胞壁聚合物（SCWP）覆盖了大部分细胞壁表面。初步分析表明，此类SCWP占细胞壁的14%，且基本由糖类组成。对细胞壁进行酶处理后发现，体外实验中SCWP是S层蛋白通过S层同源性（SLH）基序进行结合所必需的。在嗜热栖热菌生长细胞中，csaB基因对于S层-外膜（OM）复合体附着于细胞壁是必需的。体外实验证实，来自csaB突变体的细胞壁与S层的结合亲和力比野生型低得多（约为1/10）。研究发现，CsaB对于SCWP成分的丙酮酰化以及用α-SAC抗血清进行免疫检测是必需的。因此，嗜热栖热菌的S层-OM复合体通过S层蛋白的SLH基序，与SCWP的一种高度免疫原性的丙酮酰化成分发生强烈相互作用，从而与细胞壁结合。在其他嗜热栖热菌属的细胞壁以及系统发育相关的微生物耐辐射球菌中，用αSAC检测到了免疫交叉反应性化合物。这些结果表明，SLH基序与细胞壁丙酮酰化成分之间的相互作用在细菌进化早期就已出现，是一种将蛋白质和外膜锚定到原始细菌细胞壁的古老机制。
Zotero 插件