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Calcium and pH-dependent packing and release of the gel-forming MUC2 mucin.

Journal article
Authors Daniel Ambort
Malin E V Johansson
Jenny K Gustafsson
Harriet E Nilsson
Anna Ermund
Bengt R Johansson
Philip J B Koeck
Hans Hebert
Gunnar C. Hansson
Published in Proceedings of the National Academy of Sciences of the United States of America
Volume 109
Issue 15
Pages 5645-50
ISSN 1091-6490
Publication year 2012
Published at Institute of Biomedicine, Department of Medical Biochemistry and Cell Biology
Pages 5645-50
Language en
Links dx.doi.org/10.1073/pnas.1120269109
Keywords Animals, CHO Cells, Calcium, metabolism, Cricetinae, Cricetulus, Gels, metabolism, Goblet Cells, metabolism, ultrastructure, Hydrogen-Ion Concentration, Mice, Mice, Inbred C57BL, Models, Molecular, Mucin-2, chemistry, metabolism, ultrastructure, Protein Structure, Tertiary
Subject categories Cell and Molecular Biology

Abstract

MUC2, the major colonic mucin, forms large polymers by N-terminal trimerization and C-terminal dimerization. Although the assembly process for MUC2 is established, it is not known how MUC2 is packed in the regulated secretory granulae of the goblet cell. When the N-terminal VWD1-D2-D'D3 domains (MUC2-N) were expressed in a goblet-like cell line, the protein was stored together with full-length MUC2. By mimicking the pH and calcium conditions of the secretory pathway we analyzed purified MUC2-N by gel filtration, density gradient centrifugation, and transmission electron microscopy. At pH 7.4 the MUC2-N trimer eluted as a single peak by gel filtration. At pH 6.2 with Ca(2+) it formed large aggregates that did not enter the gel filtration column but were made visible after density gradient centrifugation. Electron microscopy studies revealed that the aggregates were composed of rings also observed in secretory granulae of colon tissue sections. The MUC2-N aggregates were dissolved by removing Ca(2+) and raising pH. After release from goblet cells, the unfolded full-length MUC2 formed stratified layers. These findings suggest a model for mucin packing in the granulae and the mechanism for mucin release, unfolding, and expansion.

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