Identification of an aggregation-prone structure of tau - PubMed (original) (raw)

. 2012 Oct 10;134(40):16607-13.

doi: 10.1021/ja305206m. Epub 2012 Oct 1.

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Identification of an aggregation-prone structure of tau

Shana Elbaum-Garfinkle et al. J Am Chem Soc. 2012.

Abstract

The aggregation and deposition of normally soluble proteins is the hallmark of several devastating neurodegenerative disorders. For proteins such as tau in Alzheimer's disease and α-synuclein in Parkinson's disease, aggregation involves a transition from an intrinsically disordered monomer to a highly structured fiber. While understanding the role of these proteins in neurodegeneration requires elucidation of the structural basis of self-association, the conformational heterogeneity of disordered proteins makes their structural characterization inherently challenging. Here we use single molecule Förster resonance energy transfer to measure the conformational ensemble of tau in the absence and presence of heparin to identify critical conformational changes relevant to the initiation of aggregation. We find that different domains of tau display distinct conformational properties that are strongly correlated with their degree of disorder and that may relate to their roles in aggregation. Moreover, we observe that heparin binding induces a distinct two-state structural transition in tau characterized by a loss of long-range contacts and a concomitant compaction of the microtubule binding domain. Our results describe a conformational intermediate of tau that precedes the formation of aggregates and could serve as a target for tau-focused therapeutics.

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Figures

Figure 1

Figure 1

Tau schematic. The longest full-length tau isoform (top) and the K16 fragment (bottom) are pictured. Regions of interest indicated are: the projection domain, the proline-rich region, and the MTBR (including the four repeats R1-R4). The residues mutated for labeling with fluorescent probes are shown above the schematic. Alternative splicing of two N-terminal exons and one exon in the MTBR give rise to six different tau isoforms (exon boundaries denoted with dashed lines).

Figure 2

Figure 2

Single molecule FRET histograms of eight full-length tau constructs. Representative ETeff histograms are shown for constructs 17-433 (A), 17-291 (B), 17-103 (C), 103-184 (D), 291-433 (E), 322-433 (F), 354-433 (G) and 184-291 (H) in the absence (top panels) and in the presence of 10 μM heparin (bottom panels). The mean measured ETeff (solid line) and the theoretical ETeff, ⟨E⟩, calculated for a model RC (dashed line) of each construct are indicated on the plots (see the manuscript text, SI, and Table 1). In the bottom panels of (A) and (B) the dotted gray line denotes the fit to a standard “zero-peak” to illustrate that the additional width in these distributions are due to a very low ETeff signal.

Figure 3

Figure 3

Charge screening by NaCl. ETeff histograms in 500mM NaCl are pictured for full-length constructs 244-354 (A), 354-433 (B), 17-103 (C) and 17-433 (D) with colored vertical lines indicating the peak position for each construct at 50mM NaCl. (E) Mean net charge as a function of mean hydrophobicity for all constructs; the MTBR and pro line-rich region constructs are in yellow; the C-terminal constructs are in red; the N-terminal constructs are in blue; the end-to-end construct 17-433 is in green, and the full-length protein is in grey.

Figure 4

Figure 4

Heparin binding to tau. Titration of heparin into tau results in the appearance of a distinct peak upon binding of heparin. Notably, heparin binding causes compaction in one construct (A: 244-354) and expansion of the other (B: 103-184). The concentration of heparin is noted on each panel. For details on extracted binding curves see SI text and Figure S2.

Figure 5

Figure 5

Model of conformational changes associated with population of aggregation-prone conformational ensemble. Color coding of the regions corresponds to Figure 3: projection domain (blue), MTBR (yellow), C-terminus (red) for tau in the absence (faded) and presence (bold) of heparin.

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