The Rickettsia conorii Adr1 Interacts with the C-Terminus of Human Vitronectin in a Salt-Sensitive Manner.
The Rickettsia conorii Adr1 Interacts with the C-Terminus of Human Vitronectin in a Salt-Sensitive Manner.
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DOI：
10.3389/fcimb.2017.00061
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发表时间：
2017
影响因子：
5.7
通讯作者：
Martinez JJ
中科院分区：
文献类型：
--
作者：
Fish AI;Riley SP;Singh B;Riesbeck K;Martinez JJ
斑点热族（SFG）立克次体通过食血节肢动物接种到哺乳动物的血液中。一旦进入血液并在传播过程中，这些病原体的生存取决于这些细菌逃避血清传播的宿主防御直至到达适当的细胞宿主的能力。康氏立克次体表达一种外膜蛋白 Adr1，它与补体抑制蛋白玻连蛋白结合，促进对末端补体复合物抗菌作用的抵抗。 Adr1 预计由 8 个跨膜 β 片层组成，形成一个跨膜桶，其中有 4 个暴露于细胞外环境的肽环。我们之前证明，含有环 3 或环 4 的 Adr1 衍生物在大肠杆菌外膜表达时足以结合 Vn 并介导对血清杀伤的抗性。通过在非致病性大肠杆菌表面表达 R. conorii Adr1，我们证明 Adr1 和玻连蛋白之间的相互作用是盐敏感的，并且不能通过添加肝素来中断。此外，我们利用玻连蛋白衍生肽将最小的 Adr1/玻连蛋白相互作用映射到玻连蛋白的 C 末端区域。此外，我们证明位于 Adr1 环 3 和 4 内的特定带电氨基酸残基对于介导对补体介导的杀伤的抗性至关重要。有趣的是，不再足以介导血清杀伤抗性的 Adr1 突变体仍然保留了与 Vn 结合的能力，这表明负责抗血清杀伤的 Adr1-Vn 相互作用比最初假设的更为复杂。总之，阐明 Adr1-Vn 结合的机制将有助于专门针对这种蛋白质-蛋白质相互作用进行治疗干预。
Spotted fever group (SFG) Rickettsia species are inoculated into the mammalian bloodstream by hematophagous arthropods. Once in the bloodstream and during dissemination, the survival of these pathogens is dependent upon the ability of these bacteria to evade serum-borne host defenses until a proper cellular host is reached. Rickettsia conorii expresses an outer membrane protein, Adr1, which binds the complement inhibitory protein vitronectin to promote resistance to the anti-bacterial effects of the terminal complement complex. Adr1 is predicted to consist of 8 transmembrane beta sheets that form a membrane-spanning barrel with 4 peptide loops exposed to the extracellular environment. We previously demonstrated that Adr1 derivatives containing either loop 3 or 4 are sufficient to bind Vn and mediate resistance to serum killing when expressed at the outer-membrane of E. coli. By expressing R. conorii Adr1 on the surface of non-pathogenic E. coli, we demonstrate that the interaction between Adr1 and vitronectin is salt-sensitive and cannot be interrupted by addition of heparin. Additionally, we utilized vitroenctin-derived peptides to map the minimal Adr1/vitronectin interaction to the C-terminal region of vitronectin. Furthermore, we demonstrate that specific charged amino acid residues located within loops 3 and 4 of Adr1 are critical for mediating resistance to complement-mediated killing. Interestingly, Adr1 mutants that were no longer sufficient to mediate resistance to serum killing still retained the ability to bind to Vn, suggesting that Adr1-Vn interactions responsible for resistance to serum killing are more complex than originally hypothesized. In summary, elucidation of the mechanisms governing Adr1-Vn binding will be useful to specifically target this protein-protein interaction for therapeutic intervention.