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首页> 外文期刊>Journal of Molecular Biology >TRANSMEMBRANE ALPHA-HELIX INTERACTIONS ARE REQUIRED FOR THE FUNCTIONAL ASSEMBLY OF THE ESCHERICHIA COLI TOL COMPLEX
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TRANSMEMBRANE ALPHA-HELIX INTERACTIONS ARE REQUIRED FOR THE FUNCTIONAL ASSEMBLY OF THE ESCHERICHIA COLI TOL COMPLEX

机译：大肠埃希氏菌复合物的功能性组装需要跨膜α-螺旋相互作用

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摘要

TolQ, TolR and TolA are membrane proteins involved in maintaining the structure of Escherichia coli cell envelope. TolQ and TolR span the inner membrane with three and with one a-helical segments, respectively. The tolQ925 mutation (A177V),located in the third putative transmembrane helix of TolQ (TolQ-III), induces cell sensitivity to bile salts and tolerance towards colicin A but not colicin El, unlike a null tolQ mutation, which induces tolerance to all group A colicins. Since TolQ is required for colicin A and Fl uptake, in contrast to TolR, which is necessary only for colicin A, we hypothesized that the tolQ925 mutation might affect an interaction between TolQ and TolR. We therefore searched for suppressor mutations in TolR that would restore cell envelope integrity and colicin A sensitivity to the tolQ925 mutant. Five different tolR alleles were isolated and characterized. Four of these suppressor mutations were found to be clustered in the single putative transmembrane helix of TolR (TolR-I) and one was located at the extreme C terminus of the protein. In addition, we isolated a spontaneous intragenic suppressor localized in the first transmembrane helix of TolQ (TolQ-I). These observations strongly suggest that TolR and TolQ interact via their transmembrane segments. Sequence analysis indicates that Ala177 lies on the ex-helix face of TolQ-III that, according to its composition and evolutionary conservation, is the most likely to be involved in protein/protein interaction. Energy minimization of atomic models of the wild-type and mutated forms of TolQ-III and TolR-I suggests that the deleterious effect of the A177V substitution arises from a direct steric hindrance of this residue with neighboring transmembrane segments, and that suppressor mutations may alleviate this effect either directly or indirectly, e.g. by affecting the stability of conformational equilibrium of the transmembrane region of the complex. [References: 42]
机译：TolQ，TolR和TolA是参与维持大肠杆菌细胞膜结构的膜蛋白。 TolQ和TolR分别以三个和一个a螺旋段跨越内膜。与无效的tolQ突变不同，tolQ925突变（A177V）位于TolQ的第三个推定跨膜螺旋（TolQ-III）中，可诱导细胞对胆盐的敏感性和对大肠菌素A的耐受性，但对大肠菌素El的耐受性不同大肠菌素。由于TolQ是大肠菌素A和F1吸收所必需的，与TolR相比（仅大肠菌素A是必需的），我们假设tolQ925突变可能影响TolQ和TolR之间的相互作用。因此，我们在TolR中寻找抑制突变，该突变将恢复细胞膜的完整性和大肠菌素A对tolQ925突变的敏感性。分离并表征了五个不同的tolR等位基因。发现这些抑制突变中的四个聚集在TolR的单个推定跨膜螺旋（TolR-1）中，一个位于该蛋白的C末端。此外，我们分离了位于TolQ的第一个跨膜螺旋（TolQ-1）中的自发基因内抑制子。这些观察结果强烈表明，TolR和TolQ通过其跨膜片段相互作用。序列分析表明，Ala177位于TolQ-III的前螺旋面上，根据其组成和进化保守性，它最有可能参与蛋白质/蛋白质相互作用。能量最小化的TolQ-III和TolR-I野生型和突变形式的原子模型表明，A177V取代的有害作用是由于该残基具有相邻跨膜片段的直接空间位阻，并且抑制子突变可以缓解直接或间接的这种影响，例如通过影响复合物跨膜区构象平衡的稳定性。 [参考：42]

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