Elliot Marie A, Karoonuthaisiri Nitsara, Huang Jianqiang, Bibb Maureen J, Cohen Stanley N, Kao Camilla M, Buttner Mark J
Department of Molecular Microbiology, John Innes Centre, Colney, Norwich NR4 7UH, UK.
Genes Dev. 2003 Jul 15;17(14):1727-40. doi: 10.1101/gad.264403. Epub 2003 Jun 27.
The filamentous bacterium Streptomyces coelicolor differentiates by forming specialized, spore-bearing aerial hyphae that grow into the air. Using microarrays, we identified genes that are down-regulated in a mutant unable to erect aerial hyphae. Through this route, we identified a previously unknown layer of aerial mycelium surface proteins (the "chaplins"). The chaplins share a hydrophobic domain of approximately 40 residues (the "chaplin domain"), and all have a secretion signal. The five short chaplins (ChpD,E,F,G,H) have one chaplin domain, whereas the three long chaplins (ChpA,B,C) have two chaplin domains and a C-terminal "sorting signal" that targets them for covalent attachment to the cell wall by sortase enzyme. Expression of the two chaplin genes examined (chpE, chpH) depended on aerial hyphae formation but not sporulation, and egfp fusions showed their expression localized to aerial structures. Mass spectrometry of cell wall extracts confirmed that the short chaplins localized to the cell surface. Deletion of chaplin genes caused severe delays in aerial hyphae formation, a phenotype rescued by exogenous application of chaplin proteins. These observations implicate the chaplins in aerial mycelium formation, and suggest that coating of the envelope by the chaplins is required for aerial hyphae to grow out of the aqueous environment of the substrate mycelium into the air.
丝状细菌天蓝色链霉菌通过形成生长到空气中的、带有孢子的特殊气生菌丝来进行分化。我们利用微阵列鉴定了在一个无法直立气生菌丝的突变体中表达下调的基因。通过这条途径，我们鉴定出了一层此前未知的气生菌丝表面蛋白（“chaplin蛋白”）。chaplin蛋白共享一个约40个残基的疏水结构域（“chaplin结构域”），并且都具有分泌信号。五个短chaplin蛋白（ChpD、E、F、G、H）有一个chaplin结构域，而三个长chaplin蛋白（ChpA、B、C）有两个chaplin结构域和一个C端“分选信号”，该信号通过分选酶将它们靶向共价连接到细胞壁上。所检测的两个chaplin基因（chpE、chpH）的表达依赖于气生菌丝的形成而非孢子形成，并且egfp融合蛋白显示它们的表达定位于气生结构。细胞壁提取物的质谱分析证实短chaplin蛋白定位于细胞表面。chaplin基因的缺失导致气生菌丝形成严重延迟，通过外源施加chaplin蛋白可挽救该表型。这些观察结果表明chaplin蛋白与气生菌丝的形成有关，并表明chaplin蛋白对包膜的包被是气生菌丝从基内菌丝的水环境中生长到空气中所必需的。
