title: Disulfide Mispairing During Proinsulin Folding in the Endoplasmic Reticulum.
abstract: Proinsulin folding within the endoplasmic reticulum (ER) remains incompletely understood, but it is clear that in mutant INS gene-induced diabetes of youth (MIDY), progression of the (three) native disulfide bonds of proinsulin becomes derailed, causing insulin deficiency, β-cell ER stress, and onset of diabetes. Herein, we have undertaken a molecular dissection of proinsulin disulfide bond formation, using bioengineered proinsulins that can form only two (or even only one) of the native proinsulin disulfide bonds. In the absence of preexisting proinsulin disulfide pairing, Cys(B19)-Cys(A20) (a major determinant of ER stress response activation and proinsulin stability) preferentially initiates B-A chain disulfide bond formation, whereas Cys(B7)-Cys(A7) can initiate only under oxidizing conditions beyond that existing within the ER of β-cells. Interestingly, formation of these two "interchain" disulfide bonds demonstrates cooperativity, and together, they are sufficient to confer intracellular transport competence to proinsulin. The three most common proinsulin disulfide mispairings in the ER appear to involve Cys(A11)-Cys(A20), Cys(A7)-Cys(A20), and Cys(B19)-Cys(A11), each disrupting the critical Cys(B19)-Cys(A20) pairing. MIDY mutations inhibit Cys(B19)-Cys(A20) formation, but treatment to force oxidation of this disulfide bond improves folding and results in a small but detectable increase of proinsulin export. These data suggest possible therapeutic avenues to ameliorate ER stress and diabetes.
authors.affiliation: Division of Metabolism, Endocrinology & Diabetes, University of Michigan Medical Center, Ann Arbor, MI.
authors.forename: Leena
authors.initials: L
authors.lastname: Haataja
authors.affiliation: Division of Metabolism, Endocrinology & Diabetes, University of Michigan Medical Center, Ann Arbor, MI.
authors.forename: Nandini
authors.initials: N
authors.lastname: Manickam
authors.affiliation: Division of Metabolism, Endocrinology & Diabetes, University of Michigan Medical Center, Ann Arbor, MI.
authors.forename: Ann
authors.initials: A
authors.lastname: Soliman
authors.affiliation: Department of Cell & Developmental Biology, University of Michigan Medical Center, Ann Arbor, MI.
authors.forename: Billy
authors.initials: B
authors.lastname: Tsai
authors.affiliation: Division of Metabolism, Endocrinology & Diabetes, University of Michigan Medical Center, Ann Arbor, MI Department of Endocrinology and Metabolism, Tianjin Medical University General Hospital, Tianjin, China.
authors.forename: Ming
authors.initials: M
authors.lastname: Liu
authors.affiliation: Division of Metabolism, Endocrinology & Diabetes, University of Michigan Medical Center, Ann Arbor, MI parvan@umich.edu.
authors.forename: Peter
authors.initials: P
authors.lastname: Arvan
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D003920:Diabetes Mellitus / Q000235:genetics / Q000378:metabolism; D004220:Disulfides / Q000737:chemistry / Q000378:metabolism*; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D059865:Endoplasmic Reticulum Stress / Q000502:physiology; D057809:HEK293 Cells; D006801:Humans; D007328:Insulin / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D050417:Insulin-Secreting Cells / Q000378:metabolism; D051379:Mice; D010084:Oxidation-Reduction; D018384:Oxidative Stress / Q000502:physiology; D011384:Proinsulin / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D017510:Protein Folding
chemical_list: D004220:Disulfides; D007328:Insulin; D011384:Proinsulin
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