LT-IIc, a New Member of the Type II Heat-Labile Enterotoxin Family Encoded by an Escherichia coli Strain Obtained from a Nonmammalian Host
LT-IIc, a New Member of the Type II Heat-Labile Enterotoxin Family Encoded by an Escherichia coli Strain Obtained from a Nonmammalian Host
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DOI：
10.1128/iai.00730-10
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发表时间：
2010-11-01
影响因子：
3.1
通讯作者：
Connell, Terry D.
中科院分区：
文献类型：
--
作者：
Nawar, Hesham F.;King-Lyons, Natalie D.;Connell, Terry D.
细菌不耐热肠毒素分为两类：I型HLTS由霍乱弧菌霍乱毒素(CT)、大肠杆菌LT-I和几种相关HLTS组成；II型HLTS由LT-IIa和LT-IIb组成。在此，我们报道了一种新的II型HLT，它是从禽类宿主分离的产肠毒素大肠杆菌(ETEC)株中编码的一种新的HLT。用小鼠Y1肾上腺细胞生物测定表明，LT-IIc的细胞毒性低于CT、LT-IIa或LT-IIb。LT-IIc的细胞毒作用可被识别LT-IIa或LT-IIb的抗血清部分中和，但不能被抗CT抗血清中和。编码LT-IIc A多肽和B多肽的基因排列在一个操纵子中，该操纵子的两侧是潜在的原噬菌体序列。核苷酸和预测的氨基酸序列分析表明，LT-IIc的A多肽与CT和LT-I的A多肽具有中等的同源性，与LT-IIa和LT-IIb的A多肽具有高度的同源性。LT-IIc的B多肽与CT和LT-I的B多肽没有明显的同源性，而与LT-IIa和LT-IIb的B多肽只有中等的同源性。LT-IIc与神经节苷脂的结合模式不同于LT-IIa或LT-IIb。这些数据表明，环境中还存在其他类型的II型HLT亚家族，并且II型HLT的宿主特异性可能是由介导与受体结合的B多肽的变化决定的。
Two families of bacterial heat-labile enterotoxins (HLTs) have been described: the type I HLTs are comprised of cholera toxin (CT) of Vibrio cholerae, LT-I of Escherichia coli, and several related HLTs; the type II HLTs are comprised of LT-IIa and LT-IIb. Herein, we report LT-IIc, a new type II HLT encoded from an enterotoxigenic E. coli (ETEC) strain isolated from an avian host. Using a mouse Y1 adrenal cell bioassay, LT-IIc was shown to be less cytotoxic than CT, LT-IIa, or LT-IIb. Cytotoxicity of LT-IIc was partially neutralized by antisera recognizing LT-IIa or LT-IIb but not by anti-CT antiserum. Genes encoding putative A polypeptide and B polypeptides of LT-IIc were arranged in an operon which was flanked by potential prophage sequences. Analysis of the nucleotide and predicted amino acid sequences demonstrated that the A polypeptide of LT-IIc has moderate homology to the A polypeptides of CT and LT-I and high homology to the A polypeptides of LT-IIa and LT-IIb. The B polypeptide of LT-IIc exhibited no significant homology to the B polypeptides of CT and LT-I and only moderate homology to the B polypeptides of LT-IIa and LT-IIb. The binding pattern of LT-IIc for gangliosides was distinctive from that of either LT-IIa or LT-IIb. The data suggest that other types of the type II HLT subfamily are circulating in the environment and that host specificity of type II HLT is likely governed by changes in the B polypeptide which mediate binding to receptors.