Structural Features of the Core Proteins of Human Airway Mucins Ascertained by cDNA Cloning

Abstract

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.

Coordinate Regulation of the Gel-forming Mucin Genes at Chromosome 11p15.5*

“…Each mucin gene was set to 1.0 in LS180 cells, and the other cells were calculated relative to LS180. For absolute quantification, cloned cDNAs of the four mucin genes were used as follows MUC6 (42), MUC2 (43), MUC5AC (44), and MUC5B (45). Specific picomolar amounts (determined based on plasmid size) of each cloned plasmid were used in qRT-PCR to generate a standard curve for each mucin.…”

Characterization of the human mucin gene MUC5AC: a consensus cysteine-rich domain for 11p15 mucin genes?

“…This family was described in detail [20]. The MUC5A and SC families are less known because of the numerous difficulties encountered during subcloning and sequencing [21,22]. The MUC5C family is organized into 24 bp TRs which are not strictly identical to each other and yet the amino acid consensus sequence TTSTTSAP has been deduced.…”

The role of airway mucus in pulmonary toxicology.

“…However, recent evidence obtained using methodologies that preserve the protein core of these glycoproteins, as well as new gene sequence information, suggests that there are multiple and polydisperse peptides, or apomucins (33,34). Protease-sensitive, sparsely glycosylated regions are found at both or one end of the peptide and are rich in aspartate and cysteine (approximately 13 to 16 per region).…”

“…Approximately 80% of the weight of the mucin molecule is carbohydrate (33), and these covalently attached sugars confer mucins with most of their heterogeneity and structural complexity (22). These carbohydrates are arranged in chains, called mucin type-glycans that include fucose, galactose, N-acetylglucosamine, N-acetylgalactosamine, and N-acetylneuraminic acid.…”

“…Human tracheobronchial apomucin genes have been mapped by Aubert and colleagues to chromosomes 1 p 1 5, 13, and 3 (33,67). In addition, a cystic fibrosis tracheal apomucin gene has been mapped to 1 lp13-1 1Ter (68).…”