Proteomics of regulated secretory organelles

Abstract

Regulated secretory organelles are important subcellular structures of living cells that allow the release in the extracellular space of crucial compounds, such as hormones and neurotransmitters. Therefore, the regulation of biogenesis, trafficking, and exocytosis of regulated secretory organelles has been intensively studied during the last 30 years. However, due to the large number of different regulated secretory organelles, only a few of them have been specifically characterized. New insights into regulated secretory organelles open crucial perspectives for a better comprehension of the mechanisms that govern cell secretion. The combination of subcellular fractionation, protein separation, and mass spectrometry is also possible to study regulated secretory organelles at the proteome level. In this review, we present different strategies used to isolate regulated secretory organelles, separate their protein content, and identify the proteins by mass spectrometry. The biological significance of regulated secretory organelles-proteomic analysis is discussed as well.

Platelet proteomics

“…This method can be used with a preliminary centrifugation to eliminate non-desirable organelles (Brunner et al, 2009). This strategy has been chosen by Niessen and coworkers in combination with antibody coated magnetic beads.…”

“…The separation is performed according to organelle density, shape and size. Classically, organelles are collected in a enriched fraction and their content checked by methods focusing on a particular organelle-specific marker, such as calreticuline for endoplasmic reticulum or cathepsin D for lysosomes (Righetti et al, 2005;Brunner et al, 2009). Several platelet organelles have been prefractionated using this density gradient strategy.…”

Quantitative Proteomics for Investigation of Secreted Factors: Focus on Muscle Secretome

“…Signal peptides show extreme variations in their length and amino acid composition, but do contain three distinct domains: a positively charged N-terminal region, a hydrophobic core region, typically consisting of at least 6 hydrophobic residues, and C-terminal region of polar uncharged residues (Hiller et al, 2004). Soluble proteins are transported from the Golgi to the cell exterior via the constitutive secretory pathway transporting proteins directly to the cell surface or the regulated secretory pathway in which soluble proteins and other substances are initially stored in secretory vesicles, which release proteins to the extracellular space upon extracellular signals (Brunner et al, 2009;De Matteis and Luini, 2008;Strating and Martens, 2009). The latter pathway only exists in specialized secretory cells including pancreatic β-cell releasing insulin from secretory vesicles, nerve cells, and endocrine cells.…”

Direct binding of parotid secretory protein to phosphatidylinositol phosphates.

“…It involves selective entry of the protein into the correct immature vesicle and retention of the protein as the vesicle matures [9,17]. The vesicles containing the proteins from the trans-Golgi network (TGN) traffick them to their correct final destinations [18].…”

“…One is "sorting by entry", according to which protein gets sorted directly into the vesicle from TGN [17]. This could be derived from pH/Ca++ aggregation [19], or by association of protein with the lipid rafts present in the trans-Golgi network or the protein aggregate complex binding to the TGN membrane [20].…”