Wang Tiehui, Secombes Christopher J
Scottish Fish Immunology Research Centre, University of Aberdeen, Zoology Building, Tillydrone Avenue, AB24 2TZ, Aberdeen, UK.
Immunogenetics. 2003 Dec;55(9):615-28. doi: 10.1007/s00251-003-0622-5. Epub 2003 Nov 20.
Three complement components, C1r, C4 and C1 inhibitor, of the classical activation pathway have been fully sequenced and their expression investigated in rainbow trout (Oncorhynchus mykiss). Trout C1r cDNA encodes a 707-amino-acid (aa) protein with a theoretical M(r) of 77,200. The trout translation shows highest homology with carp C1r/s, and lower, equal homologies to mammalian C1r and C1s, and MASPs from other vertebrate species. However, phylogenetic analysis and structural features suggest that the trout sequence, together with the two carp sequences, are the orthologues of mammalian C1r. The trout C4 cDNA encodes a 1,724-aa protein with a theoretical M(r) of 192,600. The trout translation shows higher homologies to the carp C4B and medaka C4, but lower homologies to C4 from other species and the carp C4A. It has a predicted signal peptide of 22 aa, a alpha-chain of 773 aa, a beta-chain of 635 aa and a lambda-chain of 288 aa. Trout C1 inhibitor cDNA encodes a 611-aa protein with a theoretical M(r) of 68,700. The trout translation has a C-terminal serpin domain with high homologies with mammalian counterparts (~37% identities), and a longer N-terminus, with no significant homology to other serpins, which contains two Ig-like domains. A molecule containing two Ig-like domains followed by a serpin domain, has also been found in an EST clone from another bony fish, the Japanese flounder. This suggests a unique structural feature of C1 inhibitor in fish. The functional significance of the Ig domains is discussed. The liver is the major site of expression of the three trout complement components, C1r, C4 and C1 inhibitor, although their expression is also detectable in other tissues. The extra-hepatic expression of complement genes may be important for local protection and inflammatory responses. Low-level constitutive expression of the three components was also detectable in a trout monocyte/macrophage cell line RTS-11, but only the expression of C4 could be upregulated by LPS.
经典激活途径的三种补体成分C1r、C4和C1抑制剂已完成全序列测定，并对其在虹鳟（Oncorhynchus mykiss）中的表达进行了研究。虹鳟C1r cDNA编码一种含707个氨基酸（aa）的蛋白质，理论分子量（M(r)）为77,200。虹鳟的翻译产物与鲤鱼C1r/s的同源性最高，与哺乳动物C1r和C1s以及其他脊椎动物物种的甘露聚糖结合凝集素相关丝氨酸蛋白酶（MASP）的同源性较低且相当。然而，系统发育分析和结构特征表明，虹鳟序列与两个鲤鱼序列一起，是哺乳动物C1r的直系同源物。虹鳟C4 cDNA编码一种含1,724个氨基酸的蛋白质，理论M(r)为192,600。虹鳟的翻译产物与鲤鱼C4B和青鳉C4的同源性较高，但与其他物种的C4和鲤鱼C4A的同源性较低。它有一个预测的22个氨基酸的信号肽、一条773个氨基酸的α链、一条635个氨基酸的β链和一条288个氨基酸的λ链。虹鳟C1抑制剂cDNA编码一种含611个氨基酸的蛋白质，理论M(r)为68,700。虹鳟的翻译产物在C末端有一个丝氨酸蛋白酶抑制剂结构域，与哺乳动物的相应结构域有高度同源性（约37%的同一性）；N末端较长，与其他丝氨酸蛋白酶抑制剂无明显同源性，其中包含两个免疫球蛋白样结构域。在另一种硬骨鱼——日本牙鲆的一个EST克隆中也发现了一种含有两个免疫球蛋白样结构域，随后是一个丝氨酸蛋白酶抑制剂结构域的分子。这表明鱼类中C1抑制剂具有独特的结构特征。文中讨论了免疫球蛋白结构域的功能意义。肝脏是虹鳟三种补体成分C1r、C4和C1抑制剂表达的主要部位，尽管在其他组织中也可检测到它们的表达。补体基因的肝外表达可能对局部保护和炎症反应很重要。在虹鳟单核细胞/巨噬细胞系RTS-11中也可检测到这三种成分的低水平组成型表达，但只有C4的表达可被脂多糖上调。
