Acidic Environment Significantly Alters Aggregation Pathway of Human Islet Amyloid Polypeptide at Negative Lipid Membrane

Abstract

The misfolding and aggregation of human islet amyloid polypeptide (hIAPP) at cell membrane has a close relationship with the development of type 2 diabetes (T2DM). This aggregation process is susceptible to various physiologically related factors, and systematic studies on condition-mediated hIAPP aggregation are therefore essential for a thorough understanding of the pathology of T2DM. In this study, we combined surface-sensitive amide I and amide II spectral signals from the protein backbone, generated simultaneously in a highly sensitive femtosecond broad-band sum frequency generation vibrational spectroscopy system, to examine the effect of environmental pH on the dynamical structural changes of hIAPP at membrane surface in situ and in real time. Such a combination can directly discriminate the formation of β-hairpin-like monomer and oligomer/fibril at the membrane surface. It is evident that, in an acidic milieu, hIAPP slows down its conformational evolution and alters its aggregation pathway, leading to the formation of off-pathway oligomers. When matured hIAPP aggregates are exposed to basic subphase, partial conversion from β-sheet oligomers into ordered β-sheet fibrillar structures is observed. When exposed to acidic environment, however, hIAPP fibrils partially converse into more loosely patterned β-sheet oligomeric structures.

Amyloid Oligomers: A Joint Experimental/Computational Perspective on Alzheimer’s Disease, Parkinson’s Disease, Type II Diabetes, and Amyotrophic Lateral Sclerosis

“…In vitro IAPP has been shown to aggregate in a concentration dependent manner, and it rapidly self assembles into amyloids when concentrated in the millimolar range, a condition that by contrast is well managed in the secretory granules of β-cells of healthy individuals. Among the factors that inhibit the aggregation of IAPP in β-cells are the acidic pH (~5.0), shown to be largely unfavorable to the misfolding of IAPP in vitro 215 , and the presence of high levels of Zn(II) in β-cells. The binding to Zn(II) indeed promotes conformations of the otherwise intrinsically disordered IAPP that are aggregation resistant, presumably by shielding the two amyloidogenic sequences of IAPP.…”

Determination of the structure and dynamics of the fuzzy coat of an amyloid fibril of IAPP using cryo-electron microscopy

“…IAPP and insulin are synthesized and stored together in pancreatic b-cells, but when IAPP aggregates in the extracellular space of the islets of Langerhans, amyloid-induced apoptosis of b-cells may occur 61 . In 95% of T2D patients, IAPP is found as extracellular amyloid deposits [62][63][64] , which form through surface-catalysed secondary nucleation 65 . IAPP fibrils represent a challenging system for structural biology studies, since no unique structure can be resolved in the low-density regions of the 12-residue long Nterminal tails, due to conformational heterogeneity and associated errors in the measurement.…”

High-Speed Atomic Force Microscopy Reveals the Structural Dynamics of the Amyloid-β and Amylin Aggregation Pathways

“…Cytosolic acidification caused by oxidative stress promoted AD [ 25 ] and Parkinson’s disease (PD) [ 26 ]. A change in pH altered the structural dynamics and aggregation pathways of Aβ [ 27 , 28 , 29 , 30 ], tau [ 31 ], α-synuclein [ 32 , 33 , 34 , 35 ], and amylin [ 36 ]. Some amyloid oligomeric conformers were more toxic than amyloid fibrils [ 37 , 38 , 39 ].…”