Kolbinger Alexandra, Gao Tong, Brock Debbie, Ammann Robin, Kisters Axel, Kellermann Joseph, Hatton Diane, Gomer Richard H, Wetterauer Birgit
Howard Hughes Medical Institute and Department of Biochemistry and Cell Biology, MS-140, Rice University, 6100 S. Main Street, Houston, TX 77005-1892, USA.
Eukaryot Cell. 2005 Jun;4(6):991-8. doi: 10.1128/EC.4.6.991-998.2005.
Much remains to be understood about quorum-sensing factors that allow cells to sense their local density. Dictyostelium discoideum is a simple eukaryote that grows as single-celled amoebae and switches to multicellular development when food becomes limited. As the growing cells reach a high density, they begin expressing discoidin genes. The cells secrete an unknown factor, and at high cell densities the concomitant high levels of the factor induce discoidin expression. We report here the enrichment of discoidin-inducing complex (DIC), an approximately 400-kDa protein complex that induces discoidin expression during growth and development. Two proteins in the DIC preparation, DicA1 and DicB, were identified by sequencing proteolytic digests. DicA1 and DicB were expressed in Escherichia coli and tested for their ability to induce discoidin during growth and development. Recombinant DicB was unable to induce discoidin expression, while recombinant DicA1 was able to induce discoidin expression. This suggests that DicA1 is an active component of DIC and indicates that posttranslational modification is dispensable for activity. DicA1 mRNA is expressed in vegetative and developing cells. The mature secreted form of DicA1 has a molecular mass of 80 kDa and has a 24-amino-acid cysteine-rich repeat that is similar to repeats in Dictyostelium proteins, such as the extracellular matrix protein ecmB/PstA, the prespore cell-inducing factor PSI, and the cyclic AMP phosphodiesterase inhibitor PDI. Together, the data suggest that DicA1 is a component of a secreted quorum-sensing signal regulating discoidin gene expression during Dictyostelium growth and development.
关于使细胞能够感知其局部密度的群体感应因子，仍有许多有待了解之处。盘基网柄菌是一种简单的真核生物，它以单细胞变形虫的形式生长，当食物变得有限时会转变为多细胞发育。随着生长的细胞达到高密度，它们开始表达盘状菌素基因。细胞分泌一种未知因子，在高细胞密度下，该因子的高水平会诱导盘状菌素表达。我们在此报告了盘状菌素诱导复合物（DIC）的富集，这是一种约400 kDa的蛋白质复合物，在生长和发育过程中诱导盘状菌素表达。通过对蛋白水解消化产物进行测序，鉴定出了DIC制剂中的两种蛋白质，即DicA1和DicB。DicA1和DicB在大肠杆菌中表达，并测试了它们在生长和发育过程中诱导盘状菌素的能力。重组DicB无法诱导盘状菌素表达，而重组DicA1能够诱导盘状菌素表达。这表明DicA1是DIC的活性成分，并表明翻译后修饰对于活性是可有可无的。DicA1 mRNA在营养细胞和发育细胞中表达。成熟的分泌形式的DicA1分子量为80 kDa，具有一个富含24个氨基酸的半胱氨酸重复序列，该序列与盘基网柄菌蛋白质中的重复序列相似，如细胞外基质蛋白ecmB/PstA、前孢子细胞诱导因子PSI和环磷酸腺苷磷酸二酯酶抑制剂PDI。总之，这些数据表明DicA1是一种分泌的群体感应信号的成分，在盘基网柄菌的生长和发育过程中调节盘状菌素基因的表达。
