Li Chenghua, Ni Duojiao, Song Linsheng, Zhao Jianmin, Zhang Huan, Li Ling
Institute of Oceanology, Chinese Academy of Sciences, Qingdao, China.
Fish Shellfish Immunol. 2008 Jan;24(1):26-34. doi: 10.1016/j.fsi.2007.06.010. Epub 2007 Jul 17.
Catalase is one of the central enzymes involved in scavenging the high level of reactive oxygen species (ROS) by degradation of hydrogen peroxide to oxygen and water. The full-length catalase cDNA of Zhikong scallop Chlamys farreri (denoted as CfCAT) was identified from hemocytes by expressed sequence tag (EST) and rapid amplification of cDNA ends (RACE) approaches. The nucleotide sequence of CfCAT cDNA consisted of 3146bp with a 5' UTR of 103bp, an unusually long 3' UTR of 1519bp with a canonical polyadenylation signal sequence AATAAA and a polyA tail, and an open reading frame (ORF) of 1521bp encoding a polypeptide of 507 amino acids with predicted molecular weight of 57.5kDa. The deduced amino acid sequence of CfCAT has significant homology to catalases from animals, plants and bacteria. Several highly conserved motifs including the proximal heme-ligand signature sequence RLFSYNDTH, the proximal active site signature FNRERIPERVVHAKGGGA, and the three catalytic amino acid residues of His(72), Asn(145) and Tyr(355) were identified in the deduced amino acid sequence of CfCAT. The CfCAT was demonstrated to be a peroxisomal glycoprotein with two potential glycosylation sites and a peroxisome targeting signal of ANL that was consistent with human, mouse and rat catalases. The time-course expression of CfCAT in hemocytes was measured by quantitative real-time PCR. The expression of CfCAT increased gradually and reached the highest point at 12h post-Vibrio infection, then recovered to the original level at 24h. All these results indicate that CfCAT, a constitutive and inducible protein, is a member of the catalase family and is involved in the process against ROS in scallop.
过氧化氢酶是通过将过氧化氢降解为氧气和水来清除高水平活性氧（ROS）的核心酶之一。采用表达序列标签（EST）和cDNA末端快速扩增（RACE）方法，从栉孔扇贝血细胞中鉴定出了栉孔扇贝过氧化氢酶的全长cDNA（命名为CfCAT）。CfCAT cDNA的核苷酸序列由3146bp组成，其中5'非翻译区（UTR）为103bp，3'UTR异常长，为1519bp，带有典型的多聚腺苷酸化信号序列AATAAA和一个多聚A尾巴，开放阅读框（ORF）为1521bp，编码一个由507个氨基酸组成的多肽，预测分子量为57.5kDa。CfCAT推导的氨基酸序列与动物、植物和细菌的过氧化氢酶具有显著同源性。在CfCAT推导的氨基酸序列中鉴定出了几个高度保守的基序，包括近端血红素配体特征序列RLFSYNDTH、近端活性位点特征FNRERIPERVVHAKGGGA以及His(72)、Asn(145)和Tyr(355)这三个催化氨基酸残基。CfCAT被证明是一种过氧化物酶体糖蛋白，有两个潜在的糖基化位点和一个与人类、小鼠和大鼠过氧化氢酶一致的过氧化物酶体靶向信号ANL。通过定量实时PCR检测了CfCAT在血细胞中的时间进程表达。CfCAT的表达逐渐增加，在感染弧菌后12小时达到最高点，然后在24小时恢复到原始水平。所有这些结果表明，CfCAT是一种组成型和诱导型蛋白，是过氧化氢酶家族的成员，参与了扇贝对抗ROS的过程。
