深海囊螂蛤铁蛋白的环境选择压力分析

Environmental selection pressure analysis of ferritin from deep-sea Vesicomyidae clams

深海环境常有高压、极端温度、富含重金属、黑暗、寡营养等特点。生活在该种特殊环境中的生物可能演绎出不同机制适应此生境。囊螂科贝类是深海冷泉/热液区的优势物种,拟通过对来自冷泉/热液区囊螂科贝类铁蛋白进行环境选择压力分析,以期解析其适应深海特殊生境(高铁环境、高静水压)的机制。通过本地比对的方式获得了囊螂蛤和其近缘种铁蛋白的核苷酸和氨基酸序列,其均有ferritin保守功能域和相应的保守位点。其中,囊螂蛤铁蛋白Cmfer-2、Cmagfer-3、Pofer-3属于M型铁蛋白,其他归属为H型铁蛋白。Cmagfer-4和Pofer-4可初步判断为分泌型铁蛋白,而其他囊螂蛤铁蛋白与胞质型铁蛋白聚为一支。为了探索环境因素对深海贝类铁蛋白的影响,运用PAML软件对深浅海铁蛋白进行了选择压力分析。结果显示总共鉴定到8个正选择位点,其后验概率大于95%。其中,在含有嗜压氨基酸的对应组中,约50%浅海位点置换为嗜压的氨基酸,进一步证明了17A、55R、171S氨基酸置换是铁蛋白适应深海压力变化的一种策略。更进一步研究发现69K→I/T/M和171E/K→S由带电荷的极性氨基酸置换为不带电荷的氨基酸,并且大部分受到选择的位点位于蛋白的N端和C端,深海囊螂蛤铁蛋白可能通过特定氨基酸极性的转变和分布区域的改变来适应深海特殊环境。本文通过深浅海贝类铁蛋白的分析来为深海生物对极端环境的适应研究提供一些信息和见解。

Deep-sea often has the characteristics of high pressure,extreme temperature,rich in heavy metals,darkness,oligotrophy and so on.Organisms living in this environment may deduce different mechanisms to adapt to this habitat.Vesicomyidae clams are the dominant species in the deep-sea cold spring/hydrothermal area.We intend to analyze the environmental selection pressure of ferritin from cold spring/hydrothermal area clams,exploring the mechanism of its adaptation to special deep-sea habitats(high iron environment,high hydrostatic pressure).The nucleotide and amino acid sequences of ferritin of clams were obtained by local blasting,which have ferritin domains and corresponding conserved sites.Among them,the ferritin Cmfer-2,Cmagfer-3 and Pofer-3 are M-type ferritins,and others belong to H-type ferritin.In addition,Cmagfer-4 and Pofer-4 can be preliminarily identified as secretory ferritin,while other Vesicomyidae ferritins clustered with cytoplasmic ferritin.In order to explore the influence of environmental factors on ferritin in deep-sea shellfish,the selection pressure of deep-sea and shallow-sea ferritin was analyzed by PAML software.A total of 8 positive selection sites were identified,and the posterior probability was greater than 95%.Among the corresponding groups containing barophilic amino acids,about 50%of shallow-water sites were replaced with barophilic amino acids,which further proved that 17A,55R and 171S amino acid substitutions were strategies for ferritin to adapt to the changes of deep-sea pressure.Then,we found that 69K→I/T/M and 171E/K→S were replaced by charged polar amino acids,and most of the selected sites were located at the N-terminal and C-terminal of the protein.The ferritins of deep-sea Vesicomyidae clams may adapt to the deep-sea environment through the change of specific amino acid polarity and distribution area.We hope to provide some information and insights for the adaptation of deep-sea organisms to extreme environments through the analysis of ferritin in deep-sea/shallow-water shellfish.