title: Molecular cloning of a major human gall bladder mucin: complete C-terminal sequence and genomic organization of MUC5B.
abstract: 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.
authors.affiliation: Section of Gastroenterology, Department of Medicine, Boston University School of Medicine and Boston City Hospital, Boston, MA 02118, USA.
authors.forename: A C
authors.initials: AC
authors.lastname: Keates
authors.forename: D P
authors.initials: DP
authors.lastname: Nunes
authors.forename: N H
authors.initials: NH
authors.lastname: Afdhal
authors.forename: R F
authors.initials: RF
authors.lastname: Troxler
authors.forename: G D
authors.initials: GD
authors.lastname: Offner
mesh_terms: D000595:Amino Acid Sequence; D001483:Base Sequence; D002918:Chymotrypsin; D003001:Cloning, Molecular; D016384:Consensus Sequence; D003545:Cysteine; D018076:DNA, Complementary; D005091:Exons; D005704:Gallbladder / Q000378:metabolism*; D015698:Genomic Library; D006801:Humans; D007438:Introns; D008969:Molecular Sequence Data; D055257:Mucin-5B; D009077:Mucins / Q000096:biosynthesis* / Q000737:chemistry / Q000235:genetics*; D009092:Mucous Membrane / Q000378:metabolism; D010446:Peptide Fragments / Q000737:chemistry; D010449:Peptide Mapping; D012091:Repetitive Sequences, Nucleic Acid; D015183:Restriction Mapping; D017386:Sequence Homology, Amino Acid; D014841:von Willebrand Factor / Q000737:chemistry / Q000235:genetics
chemical_list: D018076:DNA, Complementary; C524578:MUC5B protein, human; D055257:Mucin-5B; D009077:Mucins; D010446:Peptide Fragments; D014841:von Willebrand Factor; D002918:Chymotrypsin; D003545:Cysteine