Published ahead of print on September 7, 2006, doi:10.1165/rcmb.2006-0291TR Am. J. Respir. Cell Mol. Biol., Volume 36, Number 2, February 2007, 183-190 A more recent version of this article appeared on February 1, 2007
Submitted on August 9, 2006 Mucin Granule Intraluminal OrganizationJuan Perez-Vilar1*1 Cystic Fibrosis/Pulmonary Research and Treatment Center, University of North Carolina at Chapel Hill, School of Medicine, Chapel Hill, NC, USA * To whom correspondence should be addressed. E-mail: juan_vilar{at}med.unc.edu.
Mucus secretions have played a central role in the evolution of multicellular organisms enabling adaptation to widely differing environments. In vertebrates, mucus covers and protects the epithelial cells in the respiratory, gastrointestinal, urogenital, visual and auditory systems, amphibian's epidermis, and the gills in fishes. Deregulation of mucus production and/or composition has important consequences for human health. For instance, mucus obstruction of small airways is observed in chronic airway diseases, including COPD, asthma, and cystic fibrosis. The major protein component in the mucus is a family of large, disulfide-bonded glycoproteins known as gel-forming mucins. These proteins are accumulated in large, regulated secretory granules (the mucin granules) that occupy most of the apical cytoplasm of specialized cells known as mucous/goblet cells. Since mucin oligomers have contour dimensions larger than the mucin granule average diameter the question arises how these highly hydrophilic molecules are organized within these organelles. I review here the intraluminal organization of the mucin granule in view of our knowledge on the structure, biosynthesis, and biophysical properties of gel-forming mucins, and novel imaging studies in living mucous/goblet cells. The emerging concept is that the mucin granule lumen comprises a partially condensed matrix meshwork embedded in a fluid phase where proteins slowly diffuse.
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