R1526 residue in arginine/proinsulin binding domain of UGGT1 is involved in proinsulin binding

Abstract

Arginine releases proinsulin from binding to UGGT1 in the endoplasmic reticulum (ER). PSIPRED analysis showed that the arginine/proinsulin binding domain (A/PBD) in the C-terminal region of UGGT1 forms a disordered region, which is flexible and outside of the main protein structure. Both arginine and proinsulin may easily access the disordered region of A/PBD. Using the SNP library, two variants, Q1518∗ and R1526C, were identified in this region. UGGT1Q1518∗ protein is a deficient form of A/PBD and ER-retention signal (ERRS). UGGT1Q1518∗ protein in cell analysis reveals that mutated protein is mainly secreted from the cells because it lacks ERRS. We found another UGGT1 variant, UGGT1R1526C. At the molecular level, less interaction of proinsulin with UGGT1 was observed in both human UGGT1R1526C and mouse UGGT1L1518C with/without arginine. However, UGGT1R1526C and UGGT1WT interact with arginine similarly. We identified several amino acid residues for the arginine and proinsulin interaction. Here, the R1526 residue of UGGT1 is involved in proinsulin-interaction and is not involved in arginine-interaction.