Stability of the Agrobacterium tumefaciens VirB10 protein is modulated by growth temperature and periplasmic osmoadaption
Stability of the Agrobacterium tumefaciens VirB10 protein is modulated by growth temperature and periplasmic osmoadaption
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DOI：
10.1128/jb.180.24.6597-6606.1998
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发表时间：
1998-12-01
影响因子：
3.2
通讯作者：
Dostal, K
中科院分区：
文献类型：
--
作者：
Banta, LM;Bohne, J;Dostal, K
肿瘤农杆菌的致癌T-DNA输出是由virB操纵子的产物介导的。最近有报道（K. J. Fullner and E. W. Nester， J. bacterol . 178:1498-1504, 1996） DNA转移不发生在高温下；这些观察结果与早期关于植物冠瘿瘤发育的温度敏感性的研究相吻合。在测试这种DNA运动的损失反映了在高温下组装或维持稳定DNA转移机制的缺陷的假设时，我们发现VirB10的稳态水平对生长温度很敏感，而其他几种VirB蛋白的水平受到的影响要小得多。这种温度依赖性VirB10积累的失败在附着缺陷突变菌株（chvB）中加剧，该菌株在质周渗透适应中表现出多效性缺陷，并且可以通过降低细菌和植物组织共培养的温度来部分恢复chvB突变株的毒力。此外，在缺乏功能VirB9的细胞中，VirB10的稳定性降低，但仅在低渗透压条件下。我们认为，新合成的VirB10在存在大渗透梯度的情况下内在不稳定，除非通过virb9依赖性组装成寡聚复合物来稳定，否则它会迅速降解。含有virb10的复合物在高温下不能正确组装的可能性，为几十年前的观察提供了一种解释，即肿瘤的形成对环境温度非常敏感。
Export of oncogenic T-DNA from the phytopathogen Agrobacterium tumefaciens is mediated by the products of the virB operon. It has recently been reported (K. J. Fullner and E. W. Nester, J. Bacteriol. 178:1498-1504, 1996) that DNA transfer does not occur at elevated temperatures; these observations correlate well with much earlier studies on the temperature sensitivity of crown gall tumor development on plants. In testing the hypothesis that this loss of DNA movement reflects a defect in assembly or maintenance of a stable DNA transfer machinery at high temperature, we have found that steady-state levels of VirB10 are sensitive to growth temperature while levels of several other VirB proteins are considerably less affected. This temperature-dependent failure to accumulate VirB10 is exacerbated in an attachment-deficient mutant strain (chvB) which exhibits pleiotropic defects in periplasmic osmoadaption, and virulence of a chvB mutant can be partially restored by lowering the temperature at which the bacteria and the plant tissue are cocultivated. Furthermore, the stability of VirB10 is diminished in cells lacking functional VirB9, but only under conditions of low osmolarity. We propose that newly synthesized VirB10 is inherently labile in the presence of a large osmotic gradient across the inner membrane and is rapidly degraded unless it is stabilized by VirB9-dependent assembly into oligomeric complexes. The possibility that VirB10-containing complexes are not assembled properly at elevated temperatures suggests an explanation for the decades-old observation that tumor formation is exquisitely sensitive to ambient temperature.