The immune properties of Manduca sexta transferrin.
The immune properties of Manduca sexta transferrin.
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DOI：
10.1016/j.ibmb.2016.12.006
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发表时间：
2017-02
影响因子：
3.8
通讯作者：
Gorman MJ
中科院分区：
文献类型：
--
作者：
Brummett LM;Kanost MR;Gorman MJ
转铁蛋白是一种能结合铁的分泌型蛋白质。目前研究较多的转铁蛋白是哺乳动物血清转铁蛋白和乳铁蛋白，前者参与铁的转运，后者起免疫蛋白的作用。乳铁蛋白和乳铁蛋白衍生的多肽具有杀菌活性，而无铁形式的乳铁蛋白由于其隔离铁的能力而具有抑菌活性。昆虫转铁蛋白在序列上与血清转铁蛋白和乳铁蛋白相似，其功能尚未得到很好的描述；然而，许多对昆虫转铁蛋白的研究表明，它具有某种免疫功能。本研究的目的是确定烟草天牛转铁蛋白的特异性免疫功能。我们证实了转铁蛋白在六分枝杆菌幼虫感染后表达上调，并确定免疫攻击后血淋巴中转铁蛋白的浓度从2μM增加到10μM。它也存在于蜕皮液和预蛹中肠液中，这两种细胞外液具有免疫功能。没有观察到免疫诱导血淋巴中转铁蛋白的蛋白水解性切割；因此，六分枝杆菌转铁蛋白似乎不是抗菌肽的来源。与铁饱和乳铁蛋白不同，铁饱和转铁蛋白没有检测到的抗菌活性。相反，1μM无铁转铁蛋白抑制细菌生长，这种抑制作用可被添加1μM铁的培养基所阻断。我们的结果表明，六分枝杆菌转铁蛋白没有杀菌活性，但它确实具有抑菌功能，这依赖于它的铁隔离能力。这项研究支持这样的假设，即昆虫转铁蛋白参与了一种抑制铁的策略，以保护昆虫免受细菌感染。
Transferrins are secreted proteins that bind iron. The well-studied transferrins are mammalian serum transferrin, which is involved in iron transport, and mammalian lactoferrin, which functions as an immune protein. Lactoferrin and lactoferrin-derived peptides have bactericidal activity, and the iron-free form of lactoferrin has bacteriostatic activity due to its ability to sequester iron. Insect transferrin is similar in sequence to both serum transferrin and lactoferrin, and its functions are not well-characterized; however, many studies of insect transferrin indicate that it has some type of immune function. The goal of this study was to determine the specific immune functions of transferrin from Manduca sexta (tobacco hornworm). We verified that transferrin expression is upregulated in response to infection in M. sexta larvae and determined that the concentration of transferrin in hemolymph increases from 2 μM to 10 μM following an immune challenge. It is also present in molting fluid and prepupal midgut fluid, two extracellular fluids with immune capabilities. No immune-induced proteolytic cleavage of transferrin in hemolymph was observed; therefore, M. sexta transferrin does not appear to be a source of antimicrobial peptides. Unlike iron-saturated lactoferrin, iron-saturated transferrin had no detectable antibacterial activity. In contrast, 1 μM iron-free transferrin inhibited bacterial growth, and this inhibition was blocked by supplementing the culture medium with 1 μM iron. Our results suggest that M. sexta transferrin does not have bactericidal activity, but that it does have a bacteriostatic function that depends on its iron sequestering ability. This study supports the hypothesis that insect transferrin participates in an iron withholding strategy to protect insects from infectious bacteria.