Hinoda Y, Neumaier M, Hefta S A, Drzeniek Z, Wagener C, Shively L, Hefta L J, Shively J E, Paxton R J
Division of Immunology, Beckman Research Institute of the City of Hope, Duarte, CA 91010.
Proc Natl Acad Sci U S A. 1988 Sep;85(18):6959-63. doi: 10.1073/pnas.85.18.6959.
We have isolated and sequenced four overlapping cDNA clones from a normal adult human colon library, which together gave the entire nucleotide sequence for biliary glycoprotein I (BGP I). BGP I is a member of the carcinoembryonic antigen (CEA) gene family, which is a subfamily in the immunoglobulin gene superfamily. The deduced amino acid sequence of the combined clones for BGP I revealed a 34-residue leader sequence followed by a 108-residue N-terminal domain, a 178-residue immunoglobulin-like domain, a 108-residue region specific to BGP I, a 24-residue transmembrane domain, and a 35-residue cytoplasmic domain. The nucleotide sequence of BGP I exhibited greater than 80% identity with CEA and nonspecific crossreacting antigen (NCA) in the leader peptide, N-terminal domain, and immunoglobulin-like domain. The BGP I-specific domain, designated A', was 56.7% and 55.8% identical at the nucleotide level and 42.6% and 39.6% identical at the amino acid level to the immunoglobulin-like domain of NCA and the first immunoglobulin-like domain of CEA, respectively. Beyond nucleotide position 1375 the 3' region of the BGP I cDNA was found to be specific for BGP I. Hybridization of a probe from this region to electrophoretic blots of RNAs from different human tissues showed a predominant 2.8-kilobase (kb) message accompanied by weaker bands 4.1 and 2.1 kb in size. The same probe gave a single band in Southern blot analysis of restricted total human DNA. Using a coding region probe from the BGP I domain A', we observed 4.1- and 2.1-kb messages. Lack of the 2.8-kb band suggested that different forms of BGP I may be generated by posttranscriptional modification of the same gene. We propose that BGP I diverged from NCA by acquiring an immunoglobulin-like domain substantially different from the domains found in NCA or CEA and also a new cytoplasmic domain. The latter feature should result in a substantially different membrane anchorage mechanism of BGP I compared to CEA, which lacks the cytoplasmic domain and is anchored via a phosphatidylinositol-glycan structure. Protein structural analysis of BGP I isolated from human bile revealed a blocked N terminus, 129 amino acids of internal sequence that are in agreement with the translated cDNA sequence, and five glycosylation sites in the peptides sequenced.
我们从一个正常成人结肠文库中分离并测序了四个重叠的cDNA克隆，这些克隆共同给出了胆汁糖蛋白I（BGP I）的完整核苷酸序列。BGP I是癌胚抗原（CEA）基因家族的成员，而CEA基因家族是免疫球蛋白基因超家族中的一个亚家族。对BGP I的组合克隆推导的氨基酸序列显示，其前有一个34个残基的前导序列，接着是一个108个残基的N端结构域、一个178个残基的免疫球蛋白样结构域、一个BGP I特异的108个残基区域、一个24个残基的跨膜结构域和一个35个残基的胞质结构域。BGP I的核苷酸序列在前导肽、N端结构域和免疫球蛋白样结构域与CEA和非特异性交叉反应抗原（NCA）的一致性大于80%。BGP I特异的结构域，命名为A'，在核苷酸水平上与NCA的免疫球蛋白样结构域和CEA的第一个免疫球蛋白样结构域的一致性分别为56.7%和55.8%，在氨基酸水平上分别为42.6%和39.6%。在核苷酸位置1375之后，发现BGP I cDNA的3'区域对BGP I是特异的。用来自该区域的探针与不同人类组织RNA的电泳印迹杂交，显示出一条主要的2.8千碱基（kb）的条带，同时伴有较弱的4.1 kb和2.1 kb大小的条带。同一探针在人总DNA限制性内切酶消化后的Southern印迹分析中给出一条单一的条带。使用来自BGP I结构域A'的编码区探针，我们观察到4.1 kb和2.1 kb的条带。缺乏2.8 kb的条带表明，BGP I的不同形式可能是由同一基因的转录后修饰产生的。我们提出，BGP I与NCA发生分化是通过获得一个与NCA或CEA中发现的结构域有很大不同的免疫球蛋白样结构域以及一个新的胞质结构域。后一特征应导致BGP I与CEA相比具有显著不同的膜锚定机制，CEA缺乏胞质结构域，是通过磷脂酰肌醇聚糖结构进行锚定。从人胆汁中分离的BGP I的蛋白质结构分析显示其N端封闭，129个内部氨基酸序列与翻译的cDNA序列一致，并且在测序的肽段中有五个糖基化位点。
