Lim, M. H. | bioRxiv Science

bioRxiv2023

Dose-response relationship for the resistance of human insulin to degradation by insulin-degrading enzyme

Deeper understanding of the mechanism of the action of insulin and insulin-degrading enzyme (IDE) is a central theme in research into physiology and the pathophysiology of type 2 diabetes mellitus. Despite significant progress regarding the substrate recruitment, unfolding, digestion, and release by IDE, the structure and function of the insulin hexamer during the degradation cycle of IDE remain to be fully characterized. In the present study, we have characterized the behavior of human insulin hexamer in the absence of zinc. Using cryo-electron microscopy, we also observed that these hexamers represented a structure similar to that of T6 insulin. More interestingly, we also observed complexes in which some of their monomeric insulin components are partially distorted at their hexametric symmetry. This ensures that insulin determines the kinetics of its degradation by IDE without the requirement for zinc. These findings provide new information regarding the molecular events in insulin assembly and disassembly that permit its selective digestion by IDE.

biochemistry↗

bioRxiv2021

Dual effects of presynaptic membrane mimetics on α-synuclein amyloid aggregation

Aggregation of intrinsically disordered -synuclein (SN) under various conditions is closely related to synucleinopathies. Although various biological membranes have shown to alter the structure and aggregation propensity of SN, a thorough understanding of the molecular and mechanical mechanism of amyloidogenesis in membranes remains unanswered. Herein, we examined the structural changes, binding properties, and amyloidogenicity of three variations of SN mutants under two types of liposomes, 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) and presynaptic vesicle mimetic (Mimic) membranes. While neutrally charged DOPC membranes elicited marginal changes in the structure and amyloid fibrillation of SNs, negatively charged Mimic membranes induced dramatic helical folding and biphasic amyloid generation. At low concentration of Mimic membranes, the amyloid fibrillation of SNs was promoted in a dose-dependent manner. However, further increases in the concentration constrained the fibrillation process. These results suggest the dual effect of Mimic membranes on regulating the amyloidogenesis of SN, which is rationalized by the amyloidogenic structure of SN and condensation-dilution of local SN concentration. Finally, we propose physicochemical properties of SN and membrane surfaces, and their propensity to drive electrostatic interactions as decisive factors of amyloidogenesis.

biophysics↗