title: Surface-decoration of microtubules by human tau.
abstract: Tau is a neuronal, microtubule-associated protein that stabilizes microtubules and promotes neurite outgrowth. Tau is largely unfolded in solution and presumably forms mostly random coil. Because of its hydrophilic nature and flexible structure, tau complexed to microtubules is largely invisible by standard electron microscopy methods. We applied a combination of high-resolution metal-shadowing and cryo-electron microscopy to study the interactions between tau and microtubules. We used recombinant tau variants with different domain compositions, (1) full length tau, (2) the repeat domain that mediates microtubule binding (K19), and (3) two GFP-tau fusion proteins that contain a globular marker (GFP) attached to full-length tau at either end. All of these constructs bind exclusively to the outside of microtubules. Most of the tau-related mass appears randomly distributed, creating a "halo" of low-density mass spread across the microtubule surface. Only a small fraction of tau creates a periodic signal at an 8 nm interval, centered on alpha-tubulin subunits. Our data suggest that tau retains most of its disordered structure even when bound to the microtubule surface. Hence, it binds along, as well as across protofilaments. Nevertheless, even minute concentrations of tau have a strong stabilizing effect and effectively scavenge unpolymerized tubulin.
authors.affiliation: European Molecular Biology Laboratory, Meyerhofstrasse 1, D-69117, Heidelberg, Germany.
authors.forename: Rachel A
authors.initials: RA
authors.lastname: Santarella
authors.forename: Georgios
authors.initials: G
authors.lastname: Skiniotis
authors.forename: Kenneth N
authors.initials: KN
authors.lastname: Goldie
authors.forename: Peter
authors.initials: P
authors.lastname: Tittmann
authors.forename: Heinz
authors.initials: H
authors.lastname: Gross
authors.forename: Eva-Maria
authors.initials: EM
authors.lastname: Mandelkow
authors.forename: E
authors.initials: E
authors.lastname: Mandelkow
authors.forename: Andreas
authors.initials: A
authors.lastname: Hoenger
mesh_terms: D020285:Cryoelectron Microscopy; D006801:Humans; D016547:Kinesins / Q000737:chemistry; D008870:Microtubules / Q000737:chemistry* / Q000648:ultrastructure; D011994:Recombinant Proteins / Q000737:chemistry / Q000648:ultrastructure; D014404:Tubulin / Q000737:chemistry; D016875:tau Proteins / Q000737:chemistry*
chemical_list: D011994:Recombinant Proteins; D014404:Tubulin; D016875:tau Proteins; D016547:Kinesins