Lipidation of Class IV CdiA Effector Proteins Promotes Target Cell Recognition during Contact-Dependent Growth Inhibition.
Lipidation of Class IV CdiA Effector Proteins Promotes Target Cell Recognition during Contact-Dependent Growth Inhibition.
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DOI：
10.1128/mbio.02530-21
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发表时间：
2021-10-26
期刊：
影响因子：
6.4
通讯作者：
Hayes CS
中科院分区：
文献类型：
--
作者：
Halvorsen TM;Garza-Sánchez F;Ruhe ZC;Bartelli NL;Chan NA;Nguyen JY;Low DA;Hayes CS
接触依赖性生长抑制（CDI）系统使得蛋白质毒素能够在竞争革兰氏阴性细菌之间直接转移。CDI+菌株产生细胞表面CdiA效应蛋白，其结合邻近细菌上的特异性受体以启动毒素递送。迄今为止，已在大肠杆菌中鉴定了三类识别不同外膜蛋白受体的CdiA效应子。在这里，我们描述了第四类效应器，使用脂多糖（LPS）的核心作为受体，以确定目标细菌。对CDI抗性靶细胞的选择产生waaF和waaP“深粗”突变体，其不能合成完整的LPS核心。其他waa突变体的CDI抗性表型表明磷酸化的内核庚糖残基形成关键的CdiA识别表位。IV类cdi基因座还编码推定的赖氨酰酰基转移酶（CdiC），其与脂化毒素重复序列（RTX）溶细胞素的酶同源。我们发现，催化活性CdiC是所需的全部靶细胞杀伤活性，我们提供的证据表明，酰基转移酶附加3-羟基癸酸到一个特定的赖氨酸残基内的CdiA受体结合域。我们建议脂质部分插入到脂质A的疏水小叶中以锚CdiA与核心寡糖的相互作用。因此，LPS结合CDI系统似乎已经增选了RTX毒素活化酰基转移酶，以增加CdiA效应物对靶细胞外膜的亲和力。
Contact-dependent growth inhibition (CDI) systems enable the direct transfer of protein toxins between competing Gram-negative bacteria. CDI+ strains produce cell surface CdiA effector proteins that bind specific receptors on neighboring bacteria to initiate toxin delivery. Three classes of CdiA effectors that recognize different outer membrane protein receptors have been characterized in Escherichia coli to date. Here, we describe a fourth effector class that uses the lipopolysaccharide (LPS) core as a receptor to identify target bacteria. Selection for CDI-resistant target cells yielded waaF and waaP “deep-rough” mutants, which are unable to synthesize the full LPS core. The CDI resistance phenotypes of other waa mutants suggest that phosphorylated inner-core heptose residues form a critical CdiA recognition epitope. Class IV cdi loci also encode putative lysyl acyltransferases (CdiC) that are homologous to enzymes that lipidate repeats-in-toxin (RTX) cytolysins. We found that catalytically active CdiC is required for full target cell killing activity, and we provide evidence that the acyltransferase appends 3-hydroxydecanoate to a specific Lys residue within the CdiA receptor-binding domain. We propose that the lipid moiety inserts into the hydrophobic leaflet of lipid A to anchor CdiA interactions with the core oligosaccharide. Thus, LPS-binding CDI systems appear to have co-opted an RTX toxin-activating acyltransferase to increase the affinity of CdiA effectors for the target cell outer membrane.