The S Helix Mediates Signal Transmission as a HAMP Domain Coiled-Coil Extension in the NarX Nitrate Sensor from Escherichia coli K-12
The S Helix Mediates Signal Transmission as a HAMP Domain Coiled-Coil Extension in the NarX Nitrate Sensor from Escherichia coli K-12
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DOI：
10.1128/jb.00172-09
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发表时间：
2010-02-01
影响因子：
3.2
通讯作者：
Chen, Li-Ling
中科院分区：
文献类型：
--
作者：
Stewart, Valley;Chen, Li-Ling
在硝酸盐响应的同二聚体NarX传感器中，两个细胞质膜α螺旋划分了质周配体结合域。HAMP结构域是一个由两个α螺旋（HD1和HD2）组成的四螺旋平行螺旋，紧跟着第二个跨膜螺旋。先前的计算研究发现，在一系列信号蛋白（包括真核受体胍基环化酶）中，可能存在一种盘绕形成的α -螺旋，即信号螺旋（S螺旋），但其功能仍不清楚。在NarX中，HAMP HD2和s -螺旋区域重叠，明显形成连续的螺旋状线圈，在HD2的远端边界以七位数重复间断为标志。类似的复合hd2 - s -螺旋元件也存在于其他传感器中，例如来自酿酒酵母的Sln1p。我们在NarX S螺旋上构建了缺失和错义替换。大多数引起构成型信号表型。然而，强烈受损的诱导表型是由s -螺旋保守核心内的七磷酸腺苷缺失和七磷酸腺苷缺失引起的。后一种观察结果阐明了甲基接受趋化蛋白中邻近HAMP结构域的七肽阻滞信号传导的动态束假说的关键要素（Q. Zhou， P. Ames, and J. S. Parkinson, Mol. Microbiol. 73:801-814, 2009）。序列比较发现了在传统传感器（如CpxA、EnvZ、PhoQ和QseC）中HAMP结构域和连续的盘状七tad重复序列之间的其他七tad口吃的例子；其他s -螺旋传感器，如BarA和tor；以及粗糙神经孢子虫Nik-1 （Os-1）传感器，该传感器包含交替的HAMP和类似HAMP的元素串联阵列。因此，口吃因素可能对HAMP功能非常重要。
In the nitrate-responsive, homodimeric NarX sensor, two cytoplasmic membrane alpha-helices delimit the periplasmic ligand-binding domain. The HAMP domain, a four-helix parallel coiled-coil built from two alpha-helices (HD1 and HD2), immediately follows the second transmembrane helix. Previous computational studies identified a likely coiled-coil-forming alpha-helix, the signaling helix (S helix), in a range of signaling proteins, including eucaryal receptor guanylyl cyclases, but its function remains obscure. In NarX, the HAMP HD2 and S-helix regions overlap and apparently form a continuous coiled-coil marked by a heptad repeat stutter discontinuity at the distal boundary of HD2. Similar composite HD2-S-helix elements are present in other sensors, such as Sln1p from Saccharomyces cerevisiae. We constructed deletions and missense substitutions in the NarX S helix. Most caused constitutive signaling phenotypes. However, strongly impaired induction phenotypes were conferred by heptad deletions within the S-helix conserved core and also by deletions that remove the heptad stutter. The latter observation illuminates a key element of the dynamic bundle hypothesis for signaling across the heptad stutter adjacent to the HAMP domain in methyl-accepting chemotaxis proteins (Q. Zhou, P. Ames, and J. S. Parkinson, Mol. Microbiol. 73:801-814, 2009). Sequence comparisons identified other examples of heptad stutters between a HAMP domain and a contiguous coiled-coil-like heptad repeat sequence in conventional sensors, such as CpxA, EnvZ, PhoQ, and QseC; other S-helix-containing sensors, such as BarA and TorS; and the Neurospora crassa Nik-1 (Os-1) sensor that contains a tandem array of alternating HAMP and HAMP-like elements. Therefore, stutter elements may be broadly important for HAMP function.