Abstract
The endoplasmic reticulum (ER) plays essential roles in protein folding and assembly of secretory proteins. ER-resident molecular chaperones and related enzymes assist in protein maturation by co-operated interactions and modifications. However, the folding/assembly of multimeric proteins is not well understood. Here, we show that the maturation of fibrinogen, a hexameric secretory protein (two trimers from α, β and γ subunits), occurs in a stepwise manner. The αγ complex, a precursor for the trimer, is retained in the ER by lectin-like chaperones, and the β subunit is incorporated into the αγ complex immediately after translation. ERp57, a protein disulfide isomerase homologue, is involved in the hexamer formation from two trimers. Our results indicate that the fibrinogen hexamer is formed sequentially, rather than simultaneously, using kinetic pause by lectin chaperones. This study provides a novel insight into the assembly of most abundant multi-subunit secretory proteins.
Publication types
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Research Support, Non-U.S. Gov't
MeSH terms
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Endoplasmic Reticulum / chemistry
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Endoplasmic Reticulum / genetics
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Endoplasmic Reticulum / metabolism*
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Fibrinogen / chemistry
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Fibrinogen / genetics
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Fibrinogen / metabolism*
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Genes, Reporter
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Green Fluorescent Proteins / genetics
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Green Fluorescent Proteins / metabolism
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Hep G2 Cells
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Humans
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Kinetics
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Molecular Chaperones / antagonists & inhibitors
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Molecular Chaperones / genetics
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Molecular Chaperones / metabolism*
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Protein Biosynthesis
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Protein Disulfide-Isomerases / antagonists & inhibitors
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Protein Disulfide-Isomerases / genetics
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Protein Disulfide-Isomerases / metabolism*
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Protein Folding
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Protein Multimerization
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Protein Subunits / chemistry
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Protein Subunits / genetics
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Protein Subunits / metabolism*
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RNA, Small Interfering / genetics
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RNA, Small Interfering / metabolism
Substances
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Cyan Fluorescent Protein
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Molecular Chaperones
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Protein Subunits
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RNA, Small Interfering
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Green Fluorescent Proteins
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Fibrinogen
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Protein Disulfide-Isomerases
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PDIA3 protein, human
Grants and funding
This work was in part supported by grant-in-aid (14380295) from the Japan Society for the Promotion of Science to IW, Core Research for Evolutional Science and Technology (CREST), Japan Science and Technology Agency to TT, HN and IW, and The Uehara Memorial Foundation to TT. No additional external funding was received for this study. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.