Degenerate 87-base-pair tandem repeats create hydrophilic/hydrophobic alternating domains in human mucin peptides mapped to 11p15

A human tracheobronchial lambda gt 11 cDNA library was screened using antiserum prepared against the deglycosylated protein backbone of human tracheobronchial mucins. Two cDNAs, designated JER 28 and 57, obtained from this immunoscreening, were used to isolate two other cDNA clones, JUL 7 and JUL 10, from a human tracheobronchial lambda gt 10 cDNA library. These four clones (561, 1830, 1631 and 991 bp), which mapped to chromosome 11p15, were all found to contain degenerate 87-base-pair tandem repeats which encode non-repetitive peptides. Numerous deletions or insertions in an otherwise virtually perfect 87-base-pair tandem repeat create many shifts in reading frame which completely destroy the repetitive peptide structure. The peptide is composed of alternate hydrophobic and hydrophilic domains which probably differ in the extent to which they are glycosylated. The mRNAs are expressed both in the respiratory and in the digestive tracts. These human mucin probes may be important in assessing the abnormal mucins associated with inflammatory diseases or carcinoma from human mucosae.

Structural features of the core proteins of human airway mucins ascertained by cDNA cloning

Tracheobronchial secretions are one of the most important elements of the mucociliary system that protects the respiratory mucosa. They contain bronchial mucus, which is composed of a group of macromolecules secreted by the goblet cells of the epithelium and the submucosal glands. Bronchial mucins are the most characteristic molecules of this mucus. They form a group of complex, polydispersed O-linked glycoproteins containing sugars, which make up 80% of their weight. The protein core of human airway mucin has been difficult to sequence by traditional technologies because of its high content of serine and threonine residues linked to numerous oligosaccharide chains. We therefore prepared a lambda gt11 cDNA library from one sample of human tracheobronchial mucosa and screened this library with a polyclonal antibody directed against the apopeptides of human bronchial mucins. We obtained 20 positive clones that were sequenced. These sequences were classified into three different types. The use of the nucleotide probes from these clones in Northern blot analysis showed that the RNA messages were extremely polydispersed. At the current time, four of these probes allow us to map human tracheobronchial mucins genes to at least three different chromosomes. These results suggest that the peptide moiety of the human airway mucin is very heterogeneous.

Molecular cloning and chromosomal localization of a novel human tracheo-bronchial mucin cDNA containing tandemly repeated sequences of 48 base pairs

A lambda gt11 cDNA library constructed from human tracheo-bronchial mucosa was screened with a polyclonal antiserum raised to chemically deglycosylated pronase glycopeptides from human bronchial mucins. Out of 20 positives clones, one partial cDNA clone was isolated and allowed to map a novel human tracheo-bronchial mucin gene. It contains 48 nucleotide tandem repeats quite perfectly identical which encodes a protein containing about 50% of hydroxy amino-acids. This clone hybridized to polydisperse messages produced by human tracheo-bronchial and human colonic mucosae. The gene (proposed name MUC 4) from which cDNA is derived maps to chromosome 3.