 ICA512 RESP18 homology domain is a protein-condensing factor and insulin fibrillation inhibitor.
        ICA512 RESP18 homology domain is a protein-condensing factor and insulin fibrillation inhibitor.
     
    
        
    
    
        
        J. Biol. Chem. 294, 8564-8576 (2019)
    
    
    
      
      
	
	    Type 1 diabetes islet cell autoantigen 512 (ICA512/IA-2) is a tyrosine phosphatase-like intrinsic membrane protein involved in the biogenesis and turnover of insulin secretory granules (SGs) in pancreatic islet -cells. Whereas its membrane-proximal and cytoplasmic domains have been functionally and structurally characterized, the role of the ICA512 N-terminal segment named regulated endocrine-specific protein 18 homology domain (RESP18HD), which encompasses residues 35-131, remains largely unknown. Here, we show that ICA512 RESP18HD residues 91-131 encode for an intrinsically disordered region (IDR), which in vitro acts as a condensing factor for the reversible aggregation of insulin and other -cell proteins in a pH and Zn2+-regulated fashion. At variance with what has been shown for other granule cargoes with aggregating properties, the condensing activity of ICA512 RESP18HD is displayed at a pH close to neutral, i.e. in the pH range found in the early secretory pathway, whereas it is resolved at acidic pH and Zn2+ concentrations resembling those present in mature SGs. Moreover, we show that ICA512 RESP18HD residues 35-90, preceding the IDR, inhibit insulin fibrillation in vitro. Finally, we found that glucose-stimulated secretion of RESP18HD upon exocytosis of SGs from insulinoma INS-1 cells is associated with cleavage of its IDR, conceivably to prevent its aggregation upon exposure to neutral pH in the extracellular milieu. Taken together, these findings point to ICA512 RESP18HD being a condensing factor for protein sorting and granulogenesis early in the secretory pathway and for prevention of amyloidogenesis.
	
	
	    
	
       
      
	
	    
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        Publication type
        Article: Journal article
    
 
    
        Document type
        Scientific Article
    
 
    
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        Keywords
        Aggregation ; Amyloid ; Insulin Secretion ; Secretion ; Diabetes ; Trafficking ; Ia-2 ; Ica512 ; Protein Targeting ; Ptprn ; Secretory Granule; Secretory Granules; Targeted Disruption; Mature Ectodomain; Membrane-protein; Phase-separation; Islet Cells; Beta-cells; Glucose; Expression; Ia-2
    
 
    
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        Language
        english
    
 
    
        Publication Year
        2019
    
 
    
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        HGF-reported in Year
        2019
    
 
    
    
        ISSN (print) / ISBN
        0021-9258
    
 
    
        e-ISSN
        1083-351X
    
 
    
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	    Volume: 294,  
	    Issue: 21,  
	    Pages: 8564-8576 
	    Article Number: ,  
	    Supplement: ,  
	
    
 
    
        
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            Publisher
            American Society for Biochemistry and Molecular Biology
        
 
        
            Publishing Place
            9650 Rockville Pike, Bethesda, Md 20814-3996 Usa
        
 
	
        
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        Reviewing status
        Peer reviewed
    
 
    
        Institute(s)
        Institute of Pancreatic Islet Research (IPI)
    
 
    
        POF-Topic(s)
        90000 - German Center for Diabetes Research
    
 
    
        Research field(s)
        Helmholtz Diabetes Center
    
 
    
        PSP Element(s)
        G-502600-001
    
 
    
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        Erfassungsdatum
        2019-06-14