The type III flagellar export specificity switch is dependent on FliK ruler and a molecular clock
The type III flagellar export specificity switch is dependent on FliK ruler and a molecular clock
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DOI：
10.1016/j.jmb.2006.03.025
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发表时间：
2006-06-02
影响因子：
5.6
通讯作者：
Namba, Keiichi
中科院分区：
文献类型：
--
作者：
Moriya, Nao;Minamino, Tohru;Namba, Keiichi
沙门氏菌鞭毛钩长控制在III型鞭毛输出装置的FlhB组分的输出底物专一性水平。Flik被认为是挂钩长度传感器，并与FIhB相互作用，在挂钩完成时改变其出口专一性。为了寻找这种分子标尺所期望的Flik的性质，我们分析了Flik与挂钩的结合，发现Flik的N-末端结构域(Flik(N))与挂钩蛋白FlgD结合亲和力高，与挂钩蛋白Fige结合亲和力低。为了研究flgE在钩长控制中的可能作用，我们分离并分析了部分运动受损的flgE突变体。8个flgE突变体获得全部形成的鞭毛细丝。突变株产生的钩子明显缩短，而钩型底物如FlgE、Flik和FlgD被大量分泌，这表明突变的Fige蛋白存在钩子组装缺陷。在过度表达时，突变体Figes产生正常长度的钩子，而野生型FlgE产生更长的钩子。这些结果表明，钩子长度取决于钩子聚合速率，对于后来罕见的Flik(C)-FlhB(C)相互作用，钩子聚合的开始启动了“倒计时”，使特异性开关发生，或者在钩子长度达到约55 nm后，杆/钩型输出显著减慢。我们认为FliKN作为一种灵活的卷尺，但钩的长度也取决于钩的延长率和开关定时机制。(C)2006爱思唯尔有限公司。保留所有权利。
Salmonella flagellar hook length is controlled at the level of export substrate specificity of the FlhB component of the type III flagellar export apparatus. FliK is believed to be the hook length sensor and interacts with FIhB to change its export specificity upon hook completion. To find properties of FliK expected of such a molecular ruler, we assayed binding of FliK to the hook and found that the N-terminal domain of FliK (FliK(N)) bound to the hook-capping protein FlgD with high affinity and to the hook protein FIgE with low affinity. To investigate a possible role of FlgE in hook length control, flgE mutants with partially impaired motility were isolated and analyzed. Eight flgE mutants obtained all formed flagellar filaments. The mutants produced significantly shorter hooks while the hook-type substrates such as FlgE, FliK and FlgD were secreted in large amounts, suggesting defective hook assembly with the mutant FIgE proteins. Upon overexpression, mutant FIgEs produced hooks of normal length and wildtype FlgE produced longer hooks. These results suggest that hook length is dependent on the hook polymerization rate and that the start of hook polymerization initiates a "time countdown" for the specificity switch to occur or for significant slow down of rod/hook-type export after hook length reaches around 55 nm for later infrequent FliK(C)-FlhB(C) interaction. We propose that FliKN acts as a flexible tape measure, but that hook length is also dependent on the hook elongation rate and a switch timing mechanism. (c) 2006 Elsevier Ltd. All rights reserved.