Krishman H B, Pueppke S G
Department of Plant Pathology, University of Missouri, Columbia 65211.
Arch Microbiol. 1993;159(3):250-6. doi: 10.1007/BF00248480.
Calcium is essential for the growth of rhizobia and the formation of nitrogen-fixing root-nodules on legumes, but its precise role in these processes remains unknown. We have found that Rhizobium fredii USDA208 accumulates a major 38 kDa protein when grown in media supplemented with 0.3-2 microM Cacl2. We have purified this protein and raised polyclonal antibodies against it. The protein initially is synthesized as a 40 kDa precursor which subsequently undergoes calcium-dependent processing to give rise to the mature polypeptide. Subcellular and immunocytochemical localization studies indicate that the 38 kDa protein accumulates preferentially in the periplasmic space. Its N-terminal sequence, AETIKIGVAGPMTG, shows significant homology to the N-termini of amino acid binding proteins from the periplasm, including leucine-, isoleucine-, and valine-specific binding proteins of Pseudomonas aeruginosa and Escherichia coli and a leucine-specific binding protein of E. coli. The R. fredii protein does not, however, bind [3H]-leucine. The 38 kDa protein is encoded by the bacterial chromosome. It is absent in several rhizobia other than R. fredii, but antigenically related polypeptides are present in Escherichia coli and Erwinia carotovora subsp. carotovora.
钙对于根瘤菌的生长以及豆科植物上固氮根瘤的形成至关重要，但其在这些过程中的精确作用仍不清楚。我们发现，费氏中华根瘤菌USDA208在添加了0.3 - 2微摩尔氯化钙的培养基中生长时会积累一种主要的38 kDa蛋白。我们已纯化该蛋白并制备了针对它的多克隆抗体。该蛋白最初作为40 kDa的前体合成，随后经历钙依赖性加工以产生成熟多肽。亚细胞和免疫细胞化学定位研究表明，38 kDa蛋白优先积累在周质空间。其N端序列AETIKIGVAGPMTG与来自周质的氨基酸结合蛋白的N端具有显著同源性，包括铜绿假单胞菌和大肠杆菌的亮氨酸、异亮氨酸和缬氨酸特异性结合蛋白以及大肠杆菌的亮氨酸特异性结合蛋白。然而，费氏中华根瘤菌的这种蛋白不结合[³H] - 亮氨酸。38 kDa蛋白由细菌染色体编码。除费氏中华根瘤菌外，在其他几种根瘤菌中不存在该蛋白，但在大肠杆菌和胡萝卜软腐欧文氏菌胡萝卜亚种中存在抗原相关的多肽。
