Complementary DNA and derived amino acid sequence of the alpha subunit of human complement protein C8: evidence for the existence of a separate alpha subunit messenger RNA.
Complementary DNA and derived amino acid sequence of the alpha subunit of human complement protein C8: evidence for the existence of a separate alpha subunit messenger RNA.
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人类补体蛋白 C8 α 亚基的互补 DNA 和衍生氨基酸序列：存在单独的 α 亚基信使 RNA 的证据。
DOI：
10.1021/bi00386a046
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发表时间：
1987
期刊：
影响因子：
2.9
通讯作者：
Sodetz,JM
中科院分区：
文献类型：
--
作者：
Rao,AG;Howard,OM;Ng,SC;Whitehead,AS;Colten,HR;Sodetz,JM
南卡罗来纳大学化学系和医学院，南卡罗来纳大学哥伦比亚分校，南卡罗来纳29208，以及哈佛医学院儿童医院细胞生物学部，波士顿，马萨诸塞州02115收到1987年1月30日的摘要：通过对从人肝脏cDNA文库中分离的cDNA克隆进行表征，确定了补体（C8）第八组分a亚基（Mt 64000）的整个氨基酸序列。分离出两个重叠插入的克隆，净长度为2.44千碱基（kb），发现包含整个编码区[1659个碱基对（bp）]。5'端由一个非翻译区和一个3Q氨基酸先导序列组成。该序列包含一个明显的起始Met、信号肽和前肽，以一个富含精氨酸的序列结束，这是在蛋白质前体的前形式中发现的蛋白质水解加工位点的特征。3'非翻译区包含两个聚腺苷化信号和一个聚(a)序列。对人肝癌细胞系HepG2的细胞总RNA进行RNA印迹分析，发现其信息量约为2.5 kb。5‘和3’序列的特征和信息大小表明，一个单独的mRNA编码a，并反对在成熟的C8中发现的二硫化物连接的ay亚基的单链前体形式的出现。对衍生氨基酸序列的分析揭示了几个膜表面寻找结构域和一个可能的跨膜结构域。这些发生在亚基的无半胱氨酸区域，可能构成与靶膜相互作用的结构基础。碳水化合物组成分析表明有1或2个天冬酰胺连接的低聚糖链，但没有o -连接的低聚糖链，这与氨基酸序列的预测结果一致。a亚基包含与低密度脂蛋白受体中发现的带负电荷的富含半胱氨酸的重复序列和许多蛋白质中发现的富含半胱氨酸的表皮生长因子型序列同源的片段。最重要的是，它与人类C9具有惊人的整体同源性，在同源性基础上的值为24%，在允许保守替换的情况下为46%。随附的报告[Howard， O. M. Z., Rao， A. G., & Sodetz， J. M.(1987) Biochemistry（本期的下一篇论文）]中描述，这种同源性也延伸到C8的/3亚基。
Department of Chemistry and School of Medicine, University of South Carolina, Columbia, South Carolina 29208, and Division of Cell Biology, Children’s Hospital, Harvard Medical School, Boston, Massachusetts 02115 Received January 30, 1987 abstract: The entire amino acid sequence of the a subunit {Mt 64000) of the eighth component of complement (C8) was determined by characterizing cDNA clones isolated from a human liver cDNA library. Two clones with overlapping inserts of net length 2.44 kilobases (kb) were isolated and found to contain the entire a coding region [1659 base pairs (bp)]. The 5'end consists of an untranslated region and a leader sequence of 3Q amino acids. This sequence contains an apparent initiation Met, signal peptide, and propeptide which ends with an arginine-rich sequence that is characteristic of proteolytic processing sites found in the pro form of protein precursors. The 3'untranslated region contains two polyadenylation signals and a poly (A) sequence. RNA blot analysis of total cellular RNA from the human hepatoma cell line HepG2 revealed a message size of~ 2.5 kb. Features of the 5'and 3'sequences and the message size suggest that a separate mRNA codes for a and argues against the occurrence of a single-chain precursor form of the disulfide-linked ay subunit found in mature C8. Analysis of the derived amino acid sequence revealed several membrane surface seeking domains and a possible transmembrane domain. These occur in a cysteine-free region of the subunit and may constitute the structural basis for a interaction with target membranes. Analysis of the carbohydrate composition indicates 1 or 2 asparagine-linked but no O-linked oligosaccharidechains, a result consistent with predictions from the amino acid sequence. The a subunit contains segments homologous to the negatively charged, cysteine-rich repeat sequence found in low-density lipoprotein receptor and to the cysteine-rich epidermal growth factor type sequence found in a number of proteins. Most significantly, it exhibits a striking overall homology to human C9, with values of 24% on the basis of identity and 46% when conserved substitutions are allowed. As described in an accompanying report [Howard, O. M. Z., Rao, A. G., & Sodetz, J. M.(1987) Biochemistry (following paper in this issue)], this homology also extends to the/3 subunit of C8.