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首页> 外文期刊>Journal of Molecular Biology >Transmembrane organization of the Bacillus subtilis chemoreceptor McpB deduced by cysteine disulfide crosslinking.
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Transmembrane organization of the Bacillus subtilis chemoreceptor McpB deduced by cysteine disulfide crosslinking.

机译：半胱氨酸二硫键交联推导了枯草芽孢杆菌化学感受器McpB的跨膜组织。

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摘要

The Bacillus subtilis chemoreceptor McpB is a dimer of identical subunits containing two transmembrane (TM) segments (TM1, residues 17-34: TM2, residues 280-302) in each monomer with a 2-fold axis of symmetry. To study the organization of the TM domains, the wild-type receptor was mutated systematically at the membrane bilayer/extracytoplasmic interface with 15 single cysteine (Cys) substitutions in each of the two TM domains. Each single Cys substitution was capable of complementing a null allele in vivo, suggesting that no significant perturbation of the native tertiary or quaternary structure of the chemoreceptor was introduced by the mutations. On the basis of patterns of disulfide crosslinking between subunits of the dimeric receptor, an alpha-helical interface was identified between TM1 and TM1' (containing residues 32, 36, 39, and 43) and between TM2 and TM2' (containing residues 276, 277, 280, 283 and 286). Pairs of cysteine substitutions (positions 34/280 and 38/273) in TM1 and TM2 were used to further elucidate specific contacts within a monomer subunit, enabling a model to be constructed defining the organization of the TM domain. Crosslinking of residues that were 150-180 degrees removed from position 32 (positions 37, 41, and 44) suggested that the receptors may be organized as an array of trimers of dimers in vivo. All crosslinking was unaffected by deletion of cheB and cheR (loss of receptor demethylation/methylation enzymes) or by deletion of cheW and cheV (loss of proteins that couple receptors with the autophosphorylating kinase). These findings indicate that the organization of the transmembrane region and the stability of the quaternary complex of receptors are independent of covalent modifications of the cytoplasmic domain and conformations in the cytoplasmic domain induced by the coupling proteins.
机译：枯草芽孢杆菌化学感受器McpB是相同亚基的二聚体，在每个单体中包含两个跨膜（TM）片段（TM1，残基17-34：TM2，残基280-302），对称轴为2倍。为了研究TM结构域的组织，野生型受体在膜双层/细胞质外界面处系统突变，在两个TM结构域的每一个中都有15个单半胱氨酸（Cys）取代。每个单个的Cys替换均能够在体内补充无效等位基因，这表明突变并未导致化学感受器的天然三级或四级结构受到明显干扰。根据二聚体受体亚基之间的二硫键交联模式，在TM1和TM1'（包含残基32、36、39和43）以及TM2和TM2'（包含残基276， 277、280、283和286）。使用TM1和TM2中的成对半胱氨酸取代（位置34/280和38/273）来进一步阐明单体亚基内的特定接触，从而能够构建定义TM域结构的模型。从位置32（位置37、41和44）去除150-180度的残基的交联表明，受体可以在体内组织成一系列二聚体的三聚体。所有交联均不受cheB和cheR缺失（受体去甲基化/甲基化酶的丢失）或cheW和cheV（使受体与自磷酸化激酶偶联的蛋白质的丢失）的缺失的影响。这些发现表明跨膜区的组织和受体的季复合物的稳定性与偶联蛋白诱导的胞质结构域的共价修饰和胞质结构域的构象无关。

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