Perego M, Glaser P, Minutello A, Strauch M A, Leopold K, Fischer W
Dipartimento Farmaceutico, Facolta' di Farmacia, Universita' degli Studi di Parma, Italy.
J Biol Chem. 1995 Jun 30;270(26):15598-606. doi: 10.1074/jbc.270.26.15598.
The Bacillus subtilis dlt operon (D-alanyl-lipoteichoic acid) is responsible for D-alanine esterification of both lipoteichoic acid (LTA) and wall teichoic acid (WTA). The dlt operon contains five genes, dltA-dltE. Insertional inactivation of dltA-dltD results in complete absence of D-alanine from both LTA and WTA. Based on protein sequence similarity with the Lactobacillus casei dlt gene products (Heaton, M. P., and Neuhaus, F. C. (1992) J. Bacteriol. 174, 4707-4717), we propose that dltA encodes the D-alanine-D-alanyl carrier protein ligase (Dcl) and dltC the D-alanyl carrier protein (Dcp). We further hypothesize that the products of dltB and dltD are concerned with the transport of activated D-alanine through the membrane and the final incorporation of D-alanine into LTA. The hydropathy profiles of the dltB and dltD gene products suggest a transmembrane location for the former and an amino-terminal signal peptide for the latter. The incorporation of D-alanine into LTA and WTA did not separate in any of the mutants studied which indicates that either one and the same enzyme is responsible for D-alanine incorporation into both polymers or a separate enzyme, encoded outside the dlt operon, transfers the D-alanyl residues from LTA to WTA (Haas, R., Koch, H.-U., and Fischer, W. (1984) FEMS Microbiol. Lett. 21, 27-31). Inactivation of dltE has no effect on D-alanine ester content of both LTA and WTA, and at present we cannot propose any function for its gene product. Transcription analysis shows that the dlt operon is transcribed from a sigma D-dependent promoter and follows the pattern of transcription of genes belonging to the sigma D regulon. However, the turn off of transcription observed before sporulation starts seems to be dependent on the Spo0A and AbrB sporulation proteins and results in a D-alanine-free purely anionic LTA in the spore membrane. The dlt operon is dispensable for cell growth; its inactivation does not affect cell growth or morphology as described for L. casei.
枯草芽孢杆菌的dlt操纵子（D - 丙氨酰 - 脂磷壁酸）负责脂磷壁酸（LTA）和壁磷壁酸（WTA）的D - 丙氨酸酯化。dlt操纵子包含五个基因，即dltA - dltE。dltA - dltD的插入失活导致LTA和WTA中完全没有D - 丙氨酸。基于与干酪乳杆菌dlt基因产物的蛋白质序列相似性（希顿，M. P.，和纽豪斯，F. C.（1992年）《细菌学杂志》174，4707 - 4717），我们提出dltA编码D - 丙氨酸 - D - 丙氨酰载体蛋白连接酶（Dcl），dltC编码D - 丙氨酰载体蛋白（Dcp）。我们进一步推测dltB和dltD的产物与活化的D - 丙氨酸通过膜的转运以及D - 丙氨酸最终掺入LTA有关。dltB和dltD基因产物的亲水性图谱表明前者位于跨膜位置，后者具有氨基末端信号肽。在所研究的任何突变体中，D - 丙氨酸掺入LTA和WTA的过程都没有分离，这表明要么是同一种酶负责将D - 丙氨酸掺入这两种聚合物，要么是由dlt操纵子之外编码的一种单独的酶将D - 丙氨酰残基从LTA转移到WTA（哈斯，R.，科赫，H.-U.，和菲舍尔，W.（1984年）《微生物学快报》21，27 - 31）。dltE的失活对LTA和WTA的D - 丙氨酸酯含量没有影响，目前我们无法推测其基因产物的任何功能。转录分析表明，dlt操纵子从一个依赖于σD的启动子转录，并且遵循属于σD调控子的基因的转录模式。然而，在芽孢形成开始前观察到的转录关闭似乎依赖于Spo0A和AbrB芽孢形成蛋白，并导致芽孢膜中产生不含D - 丙氨酸且纯粹呈阴离子状态的LTA。dlt操纵子对于细胞生长是可有可无的；其失活并不影响细胞生长或形态，这与干酪乳杆菌的情况相同。
