title: Impaired processing of human pro-islet amyloid polypeptide is not a causative factor for fibril formation or membrane damage in vitro.
abstract: Human islet amyloid polypeptide (hIAPP) forms amyloid fibrils in pancreatic islets of patients with type 2 diabetes mellitus (DM2). hIAPP is synthesized by islet beta-cells initially as a preprohormone, processing of which occurs in several steps. It has been suggested that in DM2 this processing is defective and that aggregation of the processing intermediates prohIAPP and prohIAPP(1-48) may represent the initial step in formation of islet amyloid. Here we investigate this possibility by analyzing the aggregation, the structure, and the membrane interaction of mature hIAPP and its precursors, prohIAPP and prohIAPP(1-48), in vitro. Our data reveal that both precursors form amyloid fibrils in solution but not in the presence of membranes. This inhibition is in contrast to the catalyzing effect of membranes on fibril formation of mature hIAPP. Importantly, in the presence of membranes, both precursors are able to inhibit fibrillogenesis of mature hIAPP. These differences in behavior between mature hIAPP and its precursors are most likely related to differences in their mode of membrane insertion. Both precursors insert efficiently and adopt an alpha-helical structure even with a high lipid/peptide ratio, while mature hIAPP rapidly adopts a beta-sheet conformation. Furthermore, while mature hIAPP affects the barrier properties of lipid vesicles, neither of the precursors is able to induce membrane leakage. Our study suggests that the hIAPP precursors prohIAPP and prohIAPP(1-48) do not serve as amyloid initiators but rather prevent aggregation and membrane damage of mature hIAPP in early stages of its biosynthesis and intracellular transport.
authors.affiliation: Department of Chemical Biology and Organic Chemistry, Institute of Biomembranes, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands. l.p.khemtemourian@uu.nl
authors.forename: Lucie
authors.initials: L
authors.lastname: Khemtémourian
authors.forename: Gemma
authors.initials: G
authors.lastname: Lahoz Casarramona
authors.forename: Dennis P L
authors.initials: DP
authors.lastname: Suylen
authors.forename: Tilman M
authors.initials: TM
authors.lastname: Hackeng
authors.forename: Johannes D
authors.initials: JD
authors.lastname: Meeldijk
authors.forename: Ben
authors.initials: B
authors.lastname: de Kruijff
authors.forename: Jo W M
authors.initials: JW
authors.lastname: Höppener
authors.forename: J Antoinette
authors.initials: JA
authors.lastname: Killian
mesh_terms: D000682:Amyloid / Q000737:chemistry* / Q000494:pharmacology / Q000648:ultrastructure; D052160:Benzothiazoles; D002942:Circular Dichroism; D005452:Fluoresceins / Q000737:chemistry; D006801:Humans; D058228:Islet Amyloid Polypeptide; D007700:Kinetics; D008567:Membranes, Artificial; D008958:Models, Molecular; D010539:Permeability / Q000187:drug effects; D055503:Protein Multimerization / Q000502:physiology; D011499:Protein Processing, Post-Translational / Q000502:physiology*; D017433:Protein Structure, Secondary; D013050:Spectrometry, Fluorescence; D013500:Surface Tension / Q000187:drug effects; D013844:Thiazoles / Q000737:chemistry; D053835:Unilamellar Liposomes / Q000737:chemistry / Q000378:metabolism
chemical_list: D000682:Amyloid; D052160:Benzothiazoles; D005452:Fluoresceins; D058228:Islet Amyloid Polypeptide; D008567:Membranes, Artificial; D013844:Thiazoles; D053835:Unilamellar Liposomes; C422904:pro-islet amyloid polypeptide; C009462:thioflavin T; C007740:fluorexon