Economou A, Hamilton W D, Johnston A W, Downie J A
John Innes Institute, Norwich, UK.
EMBO J. 1990 Feb;9(2):349-54. doi: 10.1002/j.1460-2075.1990.tb08117.x.
Nodulation and host-specific recognition of legumes such as peas and Vicia spp. are encoded by the nodulation (nod) genes of Rhizobium leguminosarum biovar viciae. One of these genes, nodO, has been shown to encode an exported protein that contains a multiple tandem repeat of a nine amino acid domain. This domain was found to be homologous to repeated sequences in a group of bacterial exported proteins that includes haemolysin, cyclolysin, leukotoxin and two proteases. These proteins are secreted by a mechanism that does not involve an N-terminal signal peptide. The NodO protein is present in the growth medium of Rhizobium bacteria induced for nod gene expression, and partial protein sequencing of the purified protein showed that there is no N-terminal cleavage of the exported protein. It has been suggested that the internally repeated domain of haemolysin may be involved in Ca2(+)-mediated binding to erythrocytes and we show that the NodO protein can bind 45Ca2+. It is proposed that the NodO protein may interact directly with plant root cells in a Ca2(+)-dependent way, thereby mediating an early stage in the recognition that occurs between Rhizobium and its host legume.
豌豆和野豌豆属等豆科植物的结瘤及宿主特异性识别由豌豆根瘤菌蚕豆生物变种的结瘤（nod）基因编码。其中一个基因nodO已被证明编码一种输出蛋白，该蛋白包含一个由九个氨基酸结构域组成的多个串联重复序列。已发现这个结构域与一组细菌输出蛋白中的重复序列同源，这组蛋白包括溶血素、环溶血素、白细胞毒素和两种蛋白酶。这些蛋白通过一种不涉及N端信号肽的机制分泌。NodO蛋白存在于诱导结瘤基因表达的根瘤菌生长培养基中，对纯化蛋白的部分蛋白质测序表明，输出蛋白没有N端切割。有人提出溶血素的内部重复结构域可能参与Ca2 +介导的与红细胞的结合，并且我们表明NodO蛋白可以结合45Ca2 +。有人提出NodO蛋白可能以Ca2 +依赖的方式直接与植物根细胞相互作用，从而介导根瘤菌与其宿主豆科植物之间识别过程的早期阶段。
