title: Resonance Raman spectroscopic measurements delineate the structural changes that occur during tau fibril formation.
abstract: The aggregation of the microtubule-associated protein, tau, into amyloid fibrils is a hallmark of neurodegenerative diseases such as the tauopathies and Alzheimer's disease. Since monomeric tau is an intrinsically disordered protein and the polymeric fibrils possess an ordered cross-β core, the aggregation process is known to involve substantial conformational conversion besides growth. The aggregation mechanism of tau in the presence of inducers such as heparin, deciphered using probes such as thioflavin T/S fluorescence, light scattering, and electron microscopy assays, has been shown to conform to ligand-induced nucleation-dependent polymerization. These probes do not, however, distinguish between the processes of conformational conversion and fibril growth. In this study, UV resonance Raman spectroscopy is employed to look directly at signatures of changes in secondary structure and side-chain packing during fibril formation by the four repeat functional domain of tau in the presence of the inducer heparin, at pH 7 and at 37 °C. Changes in the positions and intensities of the amide Raman bands are shown to occur in two distinct stages during the fibril formation process. The first stage of UVRR spectral changes corresponds to the transformation of monomer into early fibrillar aggregates. The second stage corresponds to the transformation of these early fibrillar aggregates into the final, ordered, mature fibrils and during this stage; the processes of conformational conversion and the consolidation of the fibril core occur simultaneously. Delineation of these secondary structural changes accompanying the formation of tau fibrils holds significance for the understanding of generic and tau-specific principles of amyloid assembly.
authors.affiliation: National Centre for Biological Sciences, Tata Institute of Fundamental Research , Bangalore 560065, India.
authors.forename: Gayathri
authors.initials: G
authors.lastname: Ramachandran
authors.forename: Erix A
authors.initials: EA
authors.lastname: Milán-Garcés
authors.forename: Jayant B
authors.initials: JB
authors.lastname: Udgaonkar
authors.forename: Mrinalini
authors.initials: M
authors.lastname: Puranik
mesh_terms: D000682:Amyloid / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism / Q000648:ultrastructure; D052160:Benzothiazoles; D005456:Fluorescent Dyes; D006493:Heparin / Q000737:chemistry / Q000378:metabolism; D006801:Humans; D064267:Intrinsically Disordered Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism / Q000648:ultrastructure; D007700:Kinetics; D018625:Microscopy, Atomic Force; D008958:Models, Molecular; D066263:Protein Aggregation, Pathological; D011487:Protein Conformation; D054730:Protein Interaction Domains and Motifs; D055550:Protein Stability; D017433:Protein Structure, Secondary; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D020449:Repetitive Sequences, Amino Acid; D013050:Spectrometry, Fluorescence; D013056:Spectrophotometry, Ultraviolet; D013059:Spectrum Analysis, Raman; D013844:Thiazoles / Q000737:chemistry; D016875:tau Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism / Q000648:ultrastructure
chemical_list: D000682:Amyloid; D052160:Benzothiazoles; D005456:Fluorescent Dyes; D064267:Intrinsically Disordered Proteins; C054369:MAPT protein, human; D011994:Recombinant Proteins; D013844:Thiazoles; D016875:tau Proteins; C009462:thioflavin T; D006493:Heparin