GRANULE LATTICE PROTEIN-1 (GRL1P), AN ACIDIC, CALCIUM-BINDING PROTEININ TETRAHYMENA-THERMOPHILA DENSE-CORE SECRETORY GRANULES, INFLUENCES GRANULE SIZE, SHAPE, CONTENT ORGANIZATION, AND RELEASE BUT NOT PROTEINSORTING OR CONDENSATION

Citation
Nd. Chilcoat et al., GRANULE LATTICE PROTEIN-1 (GRL1P), AN ACIDIC, CALCIUM-BINDING PROTEININ TETRAHYMENA-THERMOPHILA DENSE-CORE SECRETORY GRANULES, INFLUENCES GRANULE SIZE, SHAPE, CONTENT ORGANIZATION, AND RELEASE BUT NOT PROTEINSORTING OR CONDENSATION, The Journal of cell biology, 135(6), 1996, pp. 1775-1787
Citations number
94
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Cell Biology
Journal title
ISSN journal
0021-9525
Volume
135
Issue
6
Year of publication
1996
Part
2
Pages
1775 - 1787
Database
ISI
SICI code
0021-9525(1996)135:6<1775:GLP(AA>2.0.ZU;2-1
Abstract
The electron-dense cores of regulated secretory granules in the ciliat e Tetrahymena thermophila are crystal lattices composed of multiple pr oteins. Granule synthesis involves a series of steps beginning with pr otein sorting, followed by the condensation and precise geometric asse mbly of the granule cargo. These steps may to various degrees be deter mined by the cargo proteins themselves. A prominent group of granule p roteins, in ciliates as well as in vertebrate neuronal and endocrine c ells, are acidic, heat-stable, and bind calcium. We focused on a prote in with these characteristics named granule lattice protein 1 (Grl1p), which represents 16% of total granule contents, and we have now clone d the corresponding gene. Mutants in which the macronuclear copies of GRL1 have been disrupted continue to synthesize dense-core granules bu t are nonetheless defective in regulated protein secretion. To underst and the nature of this defect, we characterized mutant and wild-type g ranules. In the absence of Grl1p, the sorting of the remaining granule proteins appears normal, and they condense to form a well-defined cor e, However, the condensed cores do not demonstrate a visible crystalli ne lattice, and are notably different from wild type in size and shape . The cellular secretion defect arises from failure of the aberrant gr anule cores to undergo rapid expansion and extrusion after exocytic fu sion of the granule and plasma membranes. The results suggest that sor ting, condensation, and precise granule assembly are distinct in their requirements for Grl1p.