Aims/hypothesis Components of the insulin processing and secretion pathways remain incompletely understood. Here, we examined a genome-wide association study (GWAS) signal for plasma proinsulin levels...

Lee et al. show that Ca²⁺ triggers condensates enriched with PDIA6, an ER-resident disulfide isomerase and chaperone, along with other protein disulfide isomerase family proteins and some chaperones t...

This study uses genome-wide screening and mouse genetics to uncover how cells control proinsulin, identifying the Golgi as a central hub and revealing PDIA6 as a key regulator of proinsulin production...

The insulin inhibitory receptor (inceptor) is found to bind to insulin and to regulate insulin stores by directing proinsulin and insulin towards lysosomal degradation.

Aims/hypothesis Components of the insulin processing and secretion pathways remain incompletely understood. Here, we examined a genome-wide association study (GWAS) signal for plasma proinsulin levels...

Proinsulin folding requires dynamic positioning of the C-peptide to guide A- and B-chain alignment and disulfide pairing. Mutant INS-gene-induced diabetes of youth (MIDY) arises when single-residue substitutions disrupt this process. We mapped the conformational free-energy landscapes of wild-type (WT) proinsulin and seven MIDY variants using metadynamics and molecular dynamics simulations. WT exhibits a deep free-energy minimum at compact conformations. In contrast, MIDY mutants display a continuum of destabilization: E(A4)K retains near-WT stability, Akita (C(A7)Y), V(B18)A, and R(Cpep + 2)C show moderate loss of the native basin, while H(B5)D, L(A16)P, and Y(B26)C collapse the closed–open barrier and populate misfolded open states >50% of the time. Structural analyses reveal that WT and E(A4)K preserve robust A–C docking, with the C-peptide flexibly engaging the A-chain groove. Destabilizing mutants progressively erode these native A–C contacts while forming compensatory, non-native B–C interactions. Per-residue energy decomposition highlights the loss of canonical salt bridges and emergence of aberrant electrostatic and hydrophobic hot spots, correlating with the collapse of the folding free-energy barrier. Secondary-structure analysis further shows that mutants rigidify the normally disordered C-peptide, increasing helical or strand propensity in a mutation-specific manner. Collectively, these findings establish a continuum from near-native stability to overt misfolding, mechanistically linking single-site mutations to altered folding landscapes and aggregation risk in MIDY. The results highlight the C-peptide as a dynamic linchpin of proinsulin folding and suggest that restoring its flexible docking could provide a therapeutic avenue.

The endoplasmic reticulum (ER) plays key roles in protein quality control[1][1],[2][2] and dynamic Ca2+ storage[3][3],[4][4] in eukaryotic cells. However, the protein homeostasis (proteostasis) system...

Aims/hypothesis Components of the insulin processing and secretion pathways remain incompletely understood. Here, we examined a genome-wide association study (GWAS) signal for plasma proinsulin levels. Lead GWAS variant rs150781447-T encodes an Arg279Cys substitution in TBC1 domain family member 30 (TBC1D30), but no role for this protein in insulin processing or secretion has been established previously. This study aimed to evaluate whether TBC1D30 drives the GWAS association signal by determining whether TBC1D30 is involved in proinsulin secretion and, if so, to examine the effects of variant alleles and potential mechanisms. Methods Using CRISPR/Cas9 genome editing to create double-strand breaks and prime editing to install substitutions in INS1 832/13 insulinoma cells, we generated clonal cell lines with altered TBC1D30, as well as homozygous and heterozygous lines carrying the lead GWAS variant. We characterised lines by Sanger sequencing, quantitative PCR and ELISAs to measure glu