Centre of Marine Sciences (CCMAR), Universidade do Algarve, Faro, Portugal; Department of Biomedical Sciences and Medicine (DCBM), Universidade do Algarve, Faro, Portugal.
Centre of Marine Sciences (CCMAR), Universidade do Algarve, Faro, Portugal.
Aquat Toxicol. 2020 Dec;229:105675. doi: 10.1016/j.aquatox.2020.105675. Epub 2020 Nov 5.
Iron has a fundamental role in life and in its biochemical reactions but, when in excess, it can promote the formation of free radicals which can lead to cell death. Therefore, managing the levels of iron is essential to regulate the production of oxidative stress related to iron, and ferritins are one of the main protein families involved in this process. Ferritins are ≈480 kDa multimeric proteins composed by 24 subunits, each with 19-26 kDa, which can accumulate up to 4500 iron atoms. Besides their role in managing iron bioavailability, they have also developed a role in organism immunity and defence present throughout evolution. In this work, we identified and characterized, for the first time, four different ferritin subunits in the clam Ruditapes decussatus, a bivalve commercially and ecologically important along the south Atlantic coast and in the Mediterranean basin, which is a major target of the parasitic protozoa Perkinsus olseni, considered one of the main causes of high levels of clam mortality. Following phylogenetic annotation, the four ferritins subunits identified were subdivided into two cytosolic and two secreted forms. All four subunits maintain the canonical ferritin structure with four main helices α (A-D) and a small helix (E), but the secreted ferritins present an additional helix in their N-terminal region (F), located after the signal peptide and with possible antimicrobial properties. Additionally, we identified in ferritin 4 an extra helix α (G) located between helices B and C. These alpha helix domains revealed high degree of similarity with antimicrobial peptides associated with antibacterial and antifungal activities. Analysis of the expression of these subunits showed that ferritins 1 and 2 are ubiquitously expressed while ferritins 3 and 4 are present mainly in visceral mass. Ferritin 1 lacked a putative functional iron response element (IRE) and appeared to be under a tight regulation. Ferritins 2 and 3 showed a strong response to infection by parasite Perkinsus olseni in contrast to ferritin 4, whose main response was related to exposure to a combination of metals. The synergistic effect between metals and infection promoted a general upregulation of the four ferritins. In conclusion, our results suggest that ferritins, besides their function in iron and metals detoxification, may play a determinant role in clam immune response.
铁在生命和生物化学反应中起着基础性的作用，但当铁过量时，它会促进自由基的形成，从而导致细胞死亡。因此，管理铁的水平对于调节与铁有关的氧化应激的产生至关重要，而铁蛋白是参与这一过程的主要蛋白质家族之一。铁蛋白是由 24 个亚基组成的 ≈480 kDa 多聚体蛋白，每个亚基的分子量为 19-26 kDa，可积累多达 4500 个铁原子。除了在管理铁的生物利用度方面发挥作用外，它们在生物体的免疫和防御方面也发挥了作用，这种作用在整个进化过程中都存在。在这项工作中，我们首次在蛤类大西洋帘蛤属中鉴定和表征了四种不同的铁蛋白亚基，大西洋帘蛤属是一种商业上和生态上都很重要的双壳类动物，也是寄生原生动物派琴氏虫的主要目标，派琴氏虫被认为是蛤类死亡率高的主要原因之一。经过系统发育注释，鉴定出的四种铁蛋白亚基被分为两种胞质和两种分泌形式。所有四种亚基都保持着典型的铁蛋白结构，有四个主要的α 螺旋（A-D）和一个小的α 螺旋（E），但分泌铁蛋白在其 N 端区域（F）有一个额外的螺旋，位于信号肽之后，可能具有抗菌特性。此外，我们在铁蛋白 4 中发现了一个额外的α 螺旋（G），位于β 螺旋和 C 螺旋之间。这些α 螺旋结构域与具有抗菌和抗真菌活性的抗菌肽具有高度的相似性。对这些亚基表达的分析表明，铁蛋白 1 广泛表达，而铁蛋白 2 和铁蛋白 4 主要存在于内脏团中。铁蛋白 1 缺乏一个假定的功能性铁反应元件（IRE），似乎受到严格的调控。铁蛋白 2 和铁蛋白 3 对寄生虫派琴氏虫的感染有强烈的反应，而铁蛋白 4 的主要反应则与暴露于金属混合物有关。金属和感染的协同作用促进了这四种铁蛋白的普遍上调。总之，我们的研究结果表明，铁蛋白除了在铁和金属解毒方面的功能外，在蛤类的免疫反应中可能起着决定性的作用。
