Oligomerization of Peptides LVEALYL and RGFFYT and Their Binding Affinity to Insulin

Abstract

Recently it has been proposed a model for fibrils of human insulin in which the fibril growth proceeds via stacking LVEALYL (fragment 11–17 from chain B of insulin) into pairs of tightly interdigitated -sheets. The experiments have also shown that LVEALYL has high propensity to self-assembly and binding to insulin. This necessitates study of oligomerization of LVEALYL and its binding affinity to full-length insulin. Using the all-atom simulations with Gromos96 43a1 force field and explicit water it is shown that LVEALYL can aggregate. Theoretical estimation of the binding free energy of LVEALYL to insulin by the molecular mechanic Poisson-Boltzmann surface area method reveals its strong binding affinity to chain B, implying that, in agreement with the experiments, LVEALYL can affect insulin aggregation via binding mechanism. We predict that, similar to LVEALYL, peptide RGFFYT (fragment B22-27) can self-assemble and bind to insulin modulating its fibril growth process. The binding affinity of RGFFYT is shown to be comparable with that of LVEALYL.

Equilibrium Ensembles for Insulin Folding from Bias-Exchange Metadynamics

“…Region-IV hydrophobic residues are prominently solvent exposed in the PF2 (B20 Gly, B23 Gly, B24 Phe) and the PF3 (B20 Gly, B24 Phe, B25 Phe, B26 Tyr) states. These residues are part of the RGFFYT segment speculated to modulate the insulin fibril growth process (130). In contrast, we find that a maximum of only two hydrophobic residues are solvent exposed from regions I or II in any of the PF-states, indicating these regions could be less important in contributing to early stages of insulin aggregation process.…”

“…Regions I and III have been shown to play a crucial role in the insulin fibrillation process by both aggregation incubation experiments and molecular simulations (110,118,(126)(127)(128)(129). Recently, an MD study showed that peptides from regions III and IV show similar oligomerization propensity and similar binding affinity to native insulin (130). We find the most significant exposure of hydrophobic residues in regions III and IV.…”

“…Because hydrophobic interactions are one of the main driving forces for protein folding as well as aggregation, these six residues are uniquely placed in their relevance for solution stability of insulin. Owing to exposure in the intermediate state, many of these residues have been implicated in insulin aggregation (118,128,130). However, any mutation at these sites is expected to lower the stability of the folded state.…”

Misfolded proinsulin in the endoplasmic reticulum during development of beta cell failure in diabetes

“…12 Such improperly exposed peptide sequences, especially those including the central B-chain helix LVEALYL, are thought to be aggregation prone/amyloidogenic 13 and can associate with neighboring insulin moieties, even when they are in the native state. 14 In the native state, two of the insulin disulfide bonds-C(A6)-C(A11) and C(B19)-C(A20)-are no longer exposed to solvent, and both burying and consumption of the C(A11) thiol are particularly important for the proinsulin folding pathway. 15 In beta cells, proinsulin synthesis begins as preproinsulin polyribosomes dock at the ER membrane such that the nascent translation product is translocated into the ER lumen, followed by cleavage of its signal peptide.…”

Determination of amyloid core regions of insulin analogues fibrils

“…Structural polymorphism probably leads to various surface patterns having different intra-or inter-residue arrangements [78]. Chiang et al suggested that, in addition to the B11-B17 fragment, the B22-B27 sequence can also modulate fibril growth [79]. In terms of finding the smallest amyloidogenic sequence, Swiontek et al showed that the shortest components of A13-A19, B12- B17 fragments, which contained the amino acid residues H-LeuTyr-OH (A13-A14) and H-TyrLeu-OH (B16-B17), were able to form fibrils [19].…”