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J Biol Chem. 2017 May 12;292(19):8073-8081. doi: 10.1074/jbc.M117.782284. Epub 2017 Mar 21.

Assembly-induced folding regulates interleukin 12 biogenesis and secretion.

Author information

1
From the Center for Integrated Protein Science at the Department of Chemistry and Institute for Advanced Study, Technical University of Munich, 85748 Garching, Germany and.
2
the Center of Allergy and Environment, Technical University of Munich and Helmholtz Zentrum München, 80802 Munich, Germany.
3
From the Center for Integrated Protein Science at the Department of Chemistry and Institute for Advanced Study, Technical University of Munich, 85748 Garching, Germany and matthias.feige@tum.de.

Abstract

Members of the IL-12 family perform essential functions in immunoregulation by connecting innate and adaptive immunity and are emerging therapeutic targets. They are unique among other interleukins in forming heterodimers that arise from extensive subunit sharing within the family, leading to the production of at least four functionally distinct heterodimers from only five subunits. This raises important questions about how the assembly of IL-12 family members is regulated and controlled in the cell. Here, using cell-biological approaches, we have dissected basic principles that underlie the biogenesis of the founding member of the family, IL-12. Within the native IL-12 heterodimer, composed of IL-12α and IL-12β, IL-12α possesses three intramolecular and one intermolecular disulfide bridges. We show that, in isolation, IL-12α fails to form its native structure but, instead, misfolds, forming incorrect disulfide bonds. Co-expression of its β subunit inhibits misfolding and thus allows secretion of biologically active heterodimeric IL-12. On the basis of these findings, we identified the disulfide bonds in IL-12α that are critical for assembly-induced secretion and biological activity of IL-12 versus misfolding and degradation of IL-12α. Surprisingly, two of the three disulfide bridges in IL-12α are dispensable for IL-12 secretion, stability, and biological activity. Extending our findings, we show that misfolding also occurs for IL-23α, another IL-12 family protein. Our results indicate that assembly-induced folding is key in IL-12 family biogenesis and secretion. The identification of essential disulfide bonds that underlie this process lays the basis for a simplified yet functional IL-12 cytokine.

KEYWORDS:

interleukin; protein assembly; protein folding; protein misfolding; protein secretion; protein turnover

PMID:
28325840
PMCID:
PMC5427282
DOI:
10.1074/jbc.M117.782284
[Indexed for MEDLINE]
Free PMC Article

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