A folding switch regulates interleukin 27 biogenesis and secretion of its α-subunit as a cytokine.
    
    
        
    
    
        
        Proc. Natl. Acad. Sci. U.S.A. 116, 1585-1590 (2019)
    
    
    
      
      
	
	    A common design principle of heteromeric signaling proteins is the use of shared subunits. This allows encoding of complex messages while maintaining evolutionary flexibility. How cells regulate and control assembly of such composite signaling proteins remains an important open question. An example of particular complexity and biological relevance is the interleukin 12 (IL-12) family. Four functionally distinct alpha beta heterodimers are assembled from only five subunits to regulate immune cell function and development. In addition, some subunits act as independent signaling molecules. Here we unveil key molecular mechanisms governing IL-27 biogenesis, an IL-12 family member that limits infections and autoimmunity. In mice, the IL-27 alpha subunit is secreted as a cytokine, whereas in humans only heterodimeric IL-27 is present. Surprisingly, we find that differences in a single amino acid determine if IL-27 alpha can be secreted autonomously, acting as a signaling molecule, or if it depends on hetero-dimerization for secretion. By combining computer simulations with biochemical experiments, we dissect the underlying structural determinants: a protein folding switch coupled to disulfide bond formation regulates chaperone-mediated retention versus secretion. Using these insights, we rationally change folding and assembly control for this protein. This provides the basis for a more human-like IL-27 system in mice and establishes a secretion-competent human IL-27 alpha that signals on its own and can regulate immune cell function. Taken together, our data reveal a close link between protein folding and immunoregulation. Insights into the underlying mechanisms can be used to engineer immune modulators.
	
	
	    
	
       
      
	
	    
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        Publication type
        Article: Journal article
    
 
    
        Document type
        Scientific Article
    
 
    
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        Keywords
        Protein Folding ; Protein Assembly ; Protein Quality Control ; Interleukins ; Immune Engineering; Quality-control; P40 Subunit; P35 Subunit; Il-27; Protein; Form; Receptor; Distinct; Peritonitis; Il-12p40
    
 
    
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        Publication Year
        2019
    
 
    
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        2019
    
 
    
    
        ISSN (print) / ISBN
        0027-8424
    
 
    
        e-ISSN
        1091-6490
    
 
    
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	    Volume: 116,  
	    Issue: 5,  
	    Pages: 1585-1590 
	    Article Number: ,  
	    Supplement: ,  
	
    
 
    
        
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            National Academy of Sciences
        
 
        
            Publishing Place
            2101 Constitution Ave Nw, Washington, Dc 20418 Usa
        
 
	
        
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        Reviewing status
        Peer reviewed
    
 
     
    
        POF-Topic(s)
        30202 - Environmental Health
    
 
    
        Research field(s)
        Allergy	
    
 
    
        PSP Element(s)
        G-554600-001
    
 
    
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        Erfassungsdatum
        2019-03-07