Keates A C, Nunes D P, Afdhal N H, Troxler R F, Offner G D
Section of Gastroenterology, Department of Medicine, Boston University School of Medicine and Boston City Hospital, Boston, MA 02118, USA.
Biochem J. 1997 May 15;324 ( Pt 1)(Pt 1):295-303. doi: 10.1042/bj3240295.
Gall bladder mucin has been shown to play a central role in the pathogenesis of cholesterol gallstone disease. While cloning and sequencing studies have provided a wealth of information on the structure of other gastrointestinal and respiratory mucins, nothing is known about the primary structure of human gall bladder mucin. In this study, we show that the tracheobronchial mucin MUC5B is a major mucin gene product expressed in the gall bladder. Antibodies directed against deglycosylated human gall bladder mucin were used to screen a gall bladder cDNA expression library, and most of the isolated clones contained repetitive sequences nearly identical with those in the tandem repeat region of MUC5B. An additional clone (hGBM2-3) contained an open reading frame coding for a 389 residue cysteine-rich sequence. The arrangement of cysteine residues in this sequence was very similar to that in the C-terminal regions of MUC2, MUC5AC and human von Willebrand factor. This cysteine-rich sequence was connected to a series of degenerate MUC5B tandem repeats in a 7.5 kb HincII genomic DNA fragment. This fragment, with ten exons and nine introns, contained MUC5B repeats in exon 1 and a 469 residue cysteine-rich sequence in exons 2-10 that provided a 152 nucleotide overlap with cDNA clone hGBM2-3. Interestingly, the exon-intron junctions in the MUC5B genomic fragment occurred at positions equivalent to those in the D4 domain of human von Willebrand factor, suggesting that these proteins evolved from a common evolutionary ancestor through addition or deletion of exons encoding functional domains.
胆囊黏蛋白已被证明在胆固醇结石病的发病机制中起核心作用。虽然克隆和测序研究已经提供了大量关于其他胃肠道和呼吸道黏蛋白结构的信息，但对于人胆囊黏蛋白的一级结构却一无所知。在本研究中，我们发现气管支气管黏蛋白MUC5B是在胆囊中表达的主要黏蛋白基因产物。针对去糖基化人胆囊黏蛋白的抗体被用于筛选胆囊cDNA表达文库，并且大多数分离的克隆包含与MUC5B串联重复区域中的序列几乎相同的重复序列。另外一个克隆（hGBM2-3）包含一个编码389个残基的富含半胱氨酸序列的开放阅读框。该序列中半胱氨酸残基的排列与MUC2、MUC5AC和人血管性血友病因子C末端区域中的排列非常相似。这个富含半胱氨酸的序列在一个7.5 kb的HincII基因组DNA片段中与一系列简并的MUC5B串联重复序列相连。这个片段有十个外显子和九个内含子，在外显子1中包含MUC5B重复序列，在外显子2-10中包含一个469个残基的富含半胱氨酸序列，该序列与cDNA克隆hGBM2-3有152个核苷酸的重叠。有趣的是，MUC5B基因组片段中的外显子-内含子连接位点与人类血管性血友病因子D4结构域中的位点相当，这表明这些蛋白质是通过编码功能结构域的外显子的添加或缺失从一个共同的进化祖先进化而来的。
