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首页> 外文期刊>Journal of bacteriology >Membrane topologies of the TolQ and TolR proteins of Escherichia coli: inactivation of TolQ by a missense mutation in the proposed first transmembrane segment.
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Membrane topologies of the TolQ and TolR proteins of Escherichia coli: inactivation of TolQ by a missense mutation in the proposed first transmembrane segment.

机译：大肠杆菌的TolQ和TolR蛋白的膜拓扑：建议的第一个跨膜片段中的错义突变使TolQ失活。

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The TolQ and TolR proteins of Escherichia coli are required for the uptake of group A colicins and for infection by filamentous phages. Their topology in the cytoplasmic membrane was determined by cleavage with aminopeptidase K, proteinase K, and trypsin in spheroplasts and cell lysates. From the results obtained, it is proposed that the N terminus of TolQ is located in the periplasm and that it contains three transmembrane segments (residues 9 to 36, 127 to 159, and 162 to 191), a small periplasmic loop, and two large portions in the cytoplasm. The N terminus of TolR is located in the cytoplasm and is followed by a transmembrane segment (residues 21 to 40), and the remainder of the protein is located in the periplasm. A tolQ mutant, which rendered cells resistant to group A colicins and sensitive to cholate, had alanine 13 replaced by glycine and was lacking serine 14 in the first transmembrane segment. The membrane topologies of TolQ and TolR are similar to those proposed for ExbB and ExbD, respectively, which is consistent with the partial functional substitution between ExbB and TolQ and between ExbD and TolR. The amino acid sequences of these proteins display the highest homology in the transmembrane segments, which indicates that the membrane-spanning regions play an important role in the activities of the proteins.
机译：大肠杆菌的TolQ和TolR蛋白是摄取A组大肠菌素和被丝状噬菌体感染所必需的。通过在原生质球和细胞裂解物中用氨基肽酶K，蛋白酶K和胰蛋白酶裂解来确定它们在细胞质膜中的拓扑。根据获得的结果，建议TolQ的N末端位于周质中，并包含三个跨膜片段（残基9至36、127至159和162至191），一个小的周质环和两个较大的周质环。细胞质中的部分。 TolR的N末端位于细胞质中，其后是跨膜区段（21至40位残基），其余蛋白质位于周质中。 tolQ突变体使细胞对A组大肠菌素具有抗性并对胆酸盐敏感，该突变体的丙氨酸13被甘氨酸替代，并且在第一个跨膜区段中缺少丝氨酸14。 TolQ和TolR的膜拓扑分别类似于针对ExbB和ExbD提出的膜拓扑，这与ExbB和TolQ之间以及ExbD和TolR之间的部分功能替代一致。这些蛋白质的氨基酸序列在跨膜区段中显示出最高的同源性，这表明跨膜区域在蛋白质的活性中起重要作用。

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