Abstract
Two unique nucleotide probes for human tracheobronchial mucin glycoprotein (TBM) were generated via polymerase chain reaction with degenerate primers deduced from the TBM:TR-3A tryptic peptide sequence and were used to isolate a 3.6 kilobase cDNA, clone NP3a, from a human nasal polyp cDNA library. Clone NP3a was localized to chromosome 11 and contained a 3168 nucleotide open reading frame which encoded three TBM peptide fragments, thus confirming that clone NP3a partially encodes TBM. TBM also contains five tandem repeats of TTVGP/S and an octapeptide GQCGTCTN, which is conserved in human intestinal mucin MUC2 and rat intestinal mucin-like protein (MLP) suggesting that this sequence has a functional significance for secreted mucins. TBM has amino acid similarity to the cysteine-rich domains at the carboxyl termini of MUC2, rat MLP, bovine and porcine submaxillary mucins, and human von Willebrand factor. Strikingly, a large percentage of the cysteine residues in the overlaps are highly conserved: 90% in MUC2 and von Willebrand factor, 80% of bovine submaxillary mucin, 70% in porcine submaxillary mucin, and 64% in rat MLP, suggesting that conserved cysteines may be important for the tertiary structure of secreted glycoproteins. These studies demonstrate that clone NP3a is a candidate for MUC5, making it the only human mucin gene reported to date whose gene product has been isolated from airway secretions.
Highlights
From the $Children’s Research Institute, Children’s National Medical Center and the **Department of Pediatrics and Department of Biochemistry and Molecular Biology, George Washington University, Washington D.C. 20010, the
TBM contains five tandemrepeatsof TTVGP/S andanoctapeptide GQCGTCTN, which is conservedinhumanintestinal mucin MUC2 andratintestinaml ucin-likeprotein (MLP) suggesting that this sequence has a functional amino andcarboxyl terminus domains have alsboeen reported for MUC3 (141, MUC4 [15], and MUC6 [16]
All human mucin proteins have a variable number of tandem repeats which are significance for secreted mucins.TBM has amino acid unique in sequence and size for each member of the mucin similarity to the cysteine-rich domains at the carboxyl family
Summary
Peptides were generatedby papain digestionof the TBM:TR-1 mucin glycopeptide [22] and purifiedby HPLC on a C,, column anda n ascending acetonitrile gradient. WFDMFPSPGPHGGDKETYNNI a Tryptic peptide fragment of TBM [22]. The sequence identical to TR-1:PAP-3B is underlined. TBM oligonucleotide probes from the amino acid sequence of the TBM:TR-3A tryptic peptide [22] and used them toisolate a 3.6-kb cDNA clone encoding the carboxyl terminus domain of TBM. We report the characterizationof this clone with respect to nucleotide and amino acid sequence and chromosomal localization
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