The structure of tracheobronchial mucins from cystic fibrosis and control patients.

R Gupta,N Jentoft

doi:10.1016/s0021-9258(19)50709-8

Abstract

Tracheobronchial mucin samples from control and cystic fibrosis patients were purified by gel filtration chromatography on Sephacryl S-1000 and by density gradient centrifugation. Normal secretions contained high molecular weight (approximately 10(7] mucins, whereas the cystic fibrosis secretions contained relatively small amounts of high molecular weight mucin together with larger quantities of lower molecular weight mucin fragments. These probably represent products of protease digestion. Reducing the disulfide bonds in either the control or cystic fibrosis high molecular weight mucin fractions released subunits of approximately 2000 kDa. Treating these subunits with trypsin released glycopeptides of 300 kDa. Trypsin treatment of unreduced mucin also released fragments of 2000 kDa that could be converted into 300-kDa glycopeptides upon disulfide bond reduction. Thus, protease-susceptible linkages within these mucins must be cross-linked by disulfide bonds so that the full effects of proteolytic degradation of mucins remain cryptic until disulfide bonds are reduced. Since various combinations of protease treatment and disulfide bond reduction release either 2000- or 300-kDa fragments, these fragments must represent important elements of mucin structure. The high molecular weight fractions of cystic fibrosis mucins appear to be indistinguishable from control mucins. Their amino acid compositions are the same, and various combinations of disulfide bond reduction and protease treatment release products of identical size and amino acid composition. Sulfate and carbohydrate compositions did vary considerably from sample to sample, but the limited number of samples tested did not demonstrate a cystic fibrosis-specific pattern. Thus, tracheobronchial mucins from cystic fibrosis and control patients are very similar, and both share the same generalized structure previously determined for salivary, cervical, and intestinal mucins.

Highlights

Mucous obstruction of the respiratory ages within these mucins must be cross-linkedby di- tract together with accompanying chronic pulmonary infecsulfidebonds so that the fulleffects of proteolytic tion is a devastatingaspect of the disease. These degradation of mucins remain cryptic until disulfide studies generally describe CF‘ mucins as being more highly bonds are reduced
The results indicate that mucins from CF sputum are heavily degraded
Lar weight vary widely [1,2,3,4],and it hansot been clear whether they share the same general architecture that hasbeen estab

Summary

Rekha Gupta anNd eil JentoftS

From the Departments of Pediatrics and Biochemistry, Case Western Reserve University, Cleveland,Ohio 44106. Many of the studies carriedout on pulmonary mucins have been aimed at finding differences between normal tracheomucin releasedfragments of 2000 kDa thatcould bronchial mucins and those from patients with cystic fibrosis be converted into 300-kDa glycopeptides upon disul- primarily because this disease is characterized by generalized fide bond reduction. Mucous obstruction of the respiratory ages within these mucins must be cross-linkedby di- tract together with accompanying chronic pulmonary infecsulfidebonds so that the fulleffects of proteolytic tion is a devastatingaspect of the disease. These degradation of mucins remain cryptic until disulfide studies generally describe CF‘ mucins as being more highly bonds are reduced. Lar weight vary widely [1,2,3,4],and it hansot been clear whether they share the same general architecture that hasbeen estab-

DISCUSSION

PURIFIED MUCIN

Findings

Table IV