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Identification of chondroitin sulfate linkage region glycopeptides reveals prohormones as a novel class of proteoglycans.

Journal article
Authors Fredrik Noborn
Alejandro Gomez Toledo
Carina Sihlbom
Johan Lengqvist
Erik Fries
Lena Kjellén
Jonas Nilsson
Göran Larson
Published in Molecular & cellular proteomics : MCP
Volume 14
Issue 1
Pages 41-9
ISSN 1535-9484
Publication year 2015
Published at Institute of Biomedicine, Department of Clinical Chemistry and Transfusion Medicine
Core Facilities, Proteomics
Pages 41-9
Language en
Links dx.doi.org/10.1074/mcp.M114.043703
Keywords proteoglycan, mass spectrometry, prohormone, chromogranins
Subject categories Biochemistry, Cell and Molecular Biology, Chemistry, Clinical Laboratory Medicine

Abstract

Vertebrates produce various chondroitin sulfate proteoglycans (CSPGs) that are important structural components of cartilage and other connective tissues. CSPGs also contribute to the regulation of more specialized processes such as neurogenesis and angiogenesis. Although many aspects of CSPGs have been studied extensively, little is known of where the CS chains are attached on the core proteins and so far, only a limited number of CSPGs have been identified. Obtaining global information on glycan structures and attachment sites would contribute to our understanding of the complex proteoglycan structures and may also assist in assigning CSPG specific functions. In the present work, we have developed a glycoproteomics approach that characterizes CS linkage regions, attachment sites, and identities of core proteins. CSPGs were enriched from human urine and cerebrospinal fluid samples by strong-anion-exchange chromatography, digested with chondroitinase ABC, a specific CS-lyase used to reduce the CS chain lengths and subsequently analyzed by nLC-MS/MS with a novel glycopeptide search algorithm. The protocol enabled the identification of 13 novel CSPGs, in addition to 13 previously established CSPGs, demonstrating that this approach can be routinely used to characterize CSPGs in complex human samples. Surprisingly, five of the identified CSPGs are traditionally defined as prohormones (cholecystokinin, chromogranin A, neuropeptide W, secretogranin-1, and secretogranin-3), typically stored and secreted from granules of endocrine cells. We hypothesized that the CS side chain may influence the assembly and structural organization of secretory granules and applied surface plasmon resonance spectroscopy to show that CS actually promotes the assembly of chromogranin A core proteins in vitro. This activity required mild acidic pH and suggests that the CS-side chains may also influence the self-assembly of chromogranin A in vivo giving a possible explanation to previous observations that chromogranin A has an inherent property to assemble in the acidic milieu of secretory granules.

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