HpaB from Xanthomonas campestris pv. vesicatoria acts as an exit control protein in type III-dependent protein secretion
HpaB from Xanthomonas campestris pv. vesicatoria acts as an exit control protein in type III-dependent protein secretion
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DOI：
10.1111/j.1365-2958.2004.04302.x
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发表时间：
2004-11-01
影响因子：
3.6
通讯作者：
Bonas, U
中科院分区：
文献类型：
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作者：
Büttner, D;Gürlebeck, D;Bonas, U
植物病原细菌野油菜黄单胞菌的hrp基因簇。水泡菌编码一种III型分泌系统(TTS)，该系统将细菌效应蛋白注入植物细胞。在这里，我们描述了hpaB(HPA，HRP相关)，它编码的致病因子具有TTS伴侣的典型特征。我们发现，HpaB对于至少五种效应蛋白的有效分泌是重要的，但对于非效应蛋白的分泌是必不可少的，如XopA和TTS转位蛋白HrpF。GST下拉分析表明，HpaB与两个无关的效应蛋白AvrBs1和AvrBs3相互作用，但不与XopA相互作用。HpaB结合位点位于AvrBs3的前50个氨基酸内。该区域还包含HpaB依赖的分泌的靶向信号，这在HrpF和XopA中缺失。有趣的是，HrpF和XopA的N-末端针对的是AvrBs3Delta2报告基因在DeltahpaB突变株中的易位，而不是在野生型菌株中。这表明HpaB在TTS系统的出口控制中起着至关重要的作用。我们的数据表明，HpaB促进大量效应器蛋白的分泌，并阻止非效应器蛋白进入植物细胞。
The hrp (hypersensitive response and pathogenicity) gene cluster of the plant pathogenic bacterium Xanthomonas campestris pv. vesicatoria encodes a type III secretion (TTS) system, which injects bacterial effector proteins into the plant cell. Here, we characterized hpaB (hpa, hrp-associated), which encodes a pathogenicity factor with typical features of a TTS chaperone. We show that HpaB is important for the efficient secretion of at least five effector proteins but is dispensable for the secretion of non-effectors such as XopA and the TTS translocon protein HrpF. GST pull-down assays revealed that HpaB interacts with two unrelated effector proteins, AvrBs1 and AvrBs3, but not with XopA. The HpaB-binding site is located within the first 50 amino acids of AvrBs3. This region also contains the targeting signal for HpaB-dependent secretion, which is missing in HrpF and XopA. Intriguingly, the N-termini of HrpF and XopA target the AvrBs3Delta2 reporter for translocation in a DeltahpaB mutant but not in the wild-type strain. This indicates that HpaB plays an essential role in the exit control of the TTS system. Our data suggest that HpaB promotes the secretion of a large set of effector proteins and prevents the delivery of non-effectors into the plant cell.