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bioRxiv · 10.1101/2021.05.10.442447

Distinct states of proinsulin misfolding in MIDY

Haataja, L.·Arunagiri, A.·Hassan, A.·Regan, K.·Tsai, B.·Dhayalan, B.·Weiss, M. A.·Liu, M.·Arvan, P.
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Abstract

A precondition for efficient proinsulin export from the endoplasmic reticulum (ER) is that proinsulin meets ER quality control folding requirements, including formation of the Cys(B19)-Cys(A20) "interchain" disulfide bond, facilitating formation of the Cys(B7)-Cys(A7) bridge. The third proinsulin disulfide, Cys(A6)-Cys(A11), is not required for anterograde trafficking, i.e., a "lose-A6/A11" mutant [Cys(A6), Cys(A11) both converted to Ser] is well secreted. Nevertheless, an unpaired Cys(A11) can participate in disulfide mispairings, causing ER retention of proinsulin. Among the many missense mutations causing the syndrome of Mutant INS gene-induced Diabetes of Youth (MIDY), all seem to exhibit perturbed proinsulin disulfide bond formation. Here we have examined a series of seven MIDY mutants [including G(B8)V, Y(B26)C, L(A16)P, H(B5)D, V(B18)A, R(Cpep+2)C, E(A4)K], six of which are essentially completely blocked in export from the ER in pancreatic {beta}-cells. Three of these mutants, however, must disrupt the Cys(A6)-Cys(A11) pairing to expose a critical unpaired cysteine thiol perturbation of proinsulin folding and ER export, because when introduced into the proinsulin lose-A6/A11 background, these mutants exhibit native-like disulfide bonding and improved trafficking. This maneuver also ameliorates dominant-negative blockade of export of co-expressed wild-type proinsulin. A growing molecular understanding of proinsulin misfolding may permit allele-specific pharmacological targeting for some MIDY mutants.

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Haataja, L., Arunagiri, A., Hassan, A., Regan, K., Tsai, B., Dhayalan, B., Weiss, M. A., Liu, M., Arvan, P.. 2021-05-10. Distinct states of proinsulin misfolding in MIDY. https://doi.org/10.1101/2021.05.10.442447

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