Insulin glycation by methylglyoxal results in native-like aggregation and inhibition of fibril formation

Abstract

BackgroundInsulin is a hormone that regulates blood glucose homeostasis and is a central protein in a medical condition termed insulin injection amyloidosis. It is intimately associated with glycaemia and is vulnerable to glycation by glucose and other highly reactive carbonyls like methylglyoxal, especially in diabetic conditions. Protein glycation is involved in structure and stability changes that impair protein functionality, and is associated with several human diseases, such as diabetes and neurodegenerative diseases like Alzheimer's disease, Parkinson's disease and Familiar Amyloidotic Polyneuropathy. In the present work, methylglyoxal was investigated for their effects on the structure, stability and fibril formation of insulin.ResultsMethylglyoxal was found to induce the formation of insulin native-like aggregates and reduce protein fibrillation by blocking the formation of the seeding nuclei. Equilibrium-unfolding experiments using chaotropic agents showed that glycated insulin has a small conformational stability and a weaker dependence on denaturant concentration (smaller m-value). Our observations suggest that methylglyoxal modification of insulin leads to a less compact and less stable structure that may be associated to an increased protein dynamics.ConclusionsWe propose that higher dynamics in glycated insulin could prevent the formation of the rigid cross-β core structure found in amyloid fibrils, thereby contributing to the reduction in the ability to form fibrils and to the population of different aggregation pathways like the formation of native-like aggregates.

What drives an amyloid protein precursor from an amyloidogenic to a native-like aggregation pathway?

“…In humans, native-like aggregation has been described in a very small group of proteins. Among them β-2-microglobulin is associated with dialysis-related amyloidosis, factor VIII to haemophilia A, and insulin to insulin-injection amyloidosis 12,13,35 . One study with β-2-microglobin suggests that amyloid ibril formation occurs through self-assembly of native-like intermediates 12 .…”

“…α-synuclein amyloid ibril formation seems to occur in the form of partially folded intermediate, pre-molten globule-like structure, the irst step for ibrillization 31 ( Figure 5). 13,32,33 . Unlike amyloidogenesis, native-like aggregation pathways do not present an unfolding specie to trigger oligomerization 33,34 .…”

“…The accumulation of toxic aggregates might damage the cells and progress to intra-or extra-cellular amyloid deposits 1 . Recent studies with the amyloidogenic proteins β-2-microglobulin, insulin and stefin B have shown that native-like aggregation might be associated with conformational diseases [12][13][14] . Indeed, some authors suggest that amyloidogenesis under physiological conditions follows a native-like folding aggregation 12 , whereas others argue that it must follow a misfolding pathway 13,14 .…”

“…Recent studies with the amyloidogenic proteins β-2-microglobulin, insulin and stefin B have shown that native-like aggregation might be associated with conformational diseases [12][13][14] . Indeed, some authors suggest that amyloidogenesis under physiological conditions follows a native-like folding aggregation 12 , whereas others argue that it must follow a misfolding pathway 13,14 . In spite of the lack of consensus about native-like aggregation, these investigations highlight the diversity of routes that might happen in conformational disorders.…”

Komatsuna Seed Extracts Protection Against Amyloid β(1-42)-Induced Neuronal Cell Death

“…Much attention has been paid to protein glycation as a possible factor involved in protein aggregation [7,8]. Specifically, reducing sugar plays an important role in modifying proteins, forming advanced glycation end-products (AGEs) in a non-enzymatic process called glycation.…”