Atrih A, Zöllner P, Allmaier G, Foster S J
Department of Molecular Biology and Biotechnology, University of Sheffield, United Kingdom.
J Bacteriol. 1996 Nov;178(21):6173-83. doi: 10.1128/jb.178.21.6173-6183.1996.
The structure of the endospore cell wall peptidoglycan of Bacillus subtilis has been examined. Spore peptidoglycan was produced by the development of a method based on chemical permeabilization of the spore coats and enzymatic hydrolysis of the peptidoglycan. The resulting muropeptides which were >97% pure were analyzed by reverse-phase high-performance liquid chromatography, amino acid analysis, and mass spectrometry. This revealed that 49% of the muramic acid residues in the glycan backbone were present in the delta-lactam form which occurred predominantly every second muramic acid. The glycosidic bonds adjacent to the muramic acid delta-lactam residues were resistant to the action of muramidases. Of the muramic acid residues, 25.7 and 23.3% were substituted with a tetrapeptide and a single L-alanine, respectively. Only 2% of the muramic acids had tripeptide side chains and may constitute the primordial cell wall, the remainder of the peptidoglycan being spore cortex. The spore peptidoglycan is very loosely cross-linked at only 2.9% of the muramic acid residues, a figure approximately 11-fold less than that of the vegetative cell wall. The peptidoglycan from strain AA110 (dacB) had fivefold-greater cross-linking (14.4%) than the wild type and an altered ratio of muramic acid substituents having 37.0, 46.3, and 12.3% delta-lactam, tetrapeptide, and single L-alanine, respectively. This suggests a role for the DacB protein (penicillin-binding protein 5*) in cortex biosynthesis. The sporulation-specific putative peptidoglycan hydrolase CwlD plays a pivotal role in the establishment of the mature spore cortex structure since strain AA107 (cwlD) has spore peptidoglycan which is completely devoid of muramic acid delta-lactam residues. Despite this drastic change in peptidoglycan structure, the spores are still stable but are unable to germinate. The role of delta-lactam and other spore peptidoglycan structural features in the maintenance of dormancy, heat resistance, and germination is discussed.
已对枯草芽孢杆菌芽孢细胞壁肽聚糖的结构进行了研究。芽孢肽聚糖是通过基于芽孢外壳化学通透化和肽聚糖酶解的方法制备的。对纯度大于97%的所得胞壁肽进行了反相高效液相色谱、氨基酸分析和质谱分析。结果表明，聚糖主链中49%的胞壁酸残基以δ-内酰胺形式存在，主要每隔一个胞壁酸出现一次。与胞壁酸δ-内酰胺残基相邻的糖苷键对溶菌酶的作用具有抗性。在胞壁酸残基中，分别有25.7%和23.3%被四肽和单个L-丙氨酸取代。只有2%的胞壁酸具有三肽侧链，可能构成原始细胞壁，其余的肽聚糖为芽孢皮层。芽孢肽聚糖的交联非常松散，仅2.9%的胞壁酸残基发生交联，这一数字比营养细胞壁约少11倍。来自AA110菌株（dacB）的肽聚糖交联程度（14.4%）比野生型高五倍，并且胞壁酸取代基的比例发生了变化，分别为37.0%、46.3%和12.3%的δ-内酰胺、四肽和单个L-丙氨酸。这表明DacB蛋白（青霉素结合蛋白5*）在皮层生物合成中起作用。芽孢形成特异性假定的肽聚糖水解酶CwlD在成熟芽孢皮层结构的形成中起关键作用，因为AA107菌株（cwlD）的芽孢肽聚糖完全没有胞壁酸δ-内酰胺残基。尽管肽聚糖结构发生了如此剧烈的变化，但芽孢仍然稳定但无法萌发。讨论了δ-内酰胺和其他芽孢肽聚糖结构特征在维持休眠、耐热性和萌发中的作用。
