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Proc. Natl. Acad. Sci. USA, November 24, 2015 vol. 112 no. 47 E6416-E6425 | doi: 10.1073/pnas.1513172112 Direct force measurements reveal that protein Tau confers short-range attractions and isoform-dependent steric stabilization to microtubules

Abstract

Peter J. Chung^a,b,c,1, Myung Chul Choi^d,1, Herbert P. Miller^c,e, H. Eric Feinstein^c,e,2, Uri Raviv^f, Youli Li^g, Leslie Wilson^c,e, Stuart C. Feinstein^c,e, and Cyrus R. Safinya^a,b,c,3

^aMaterials Department, University of California, Santa Barbara, CA 93106;

^bPhysics Department, University of California, Santa Barbara, CA 93106;

^cMolecular, Cellular, and Developmental Biology Department, University of California, Santa Barbara, CA 93106;

^dDepartment of Bio and Brain Engineering, Korea Advanced Institute of Science and Technology, Daejeon 305-701, Republic of Korea;

^eNeuroscience Research Institute, University of California, Santa Barbara, CA 93106;

^fInstitute of Chemistry, Hebrew University of Jerusalem, Jerusalem 91904, Israel;

^gMaterials Research Laboratory, University of California, Santa Barbara, CA 93106

Abstract

Microtubules (MTs) are hollow cytoskeletal filaments assembled from αβ-tubulin heterodimers. Tau, an unstructured protein found in neuronal axons, binds to MTs and regulates their dynamics. Aberrant Tau behavior is associated with neurodegenerative dementias, including Alzheimer’s. Here, we report on a direct force measurement between paclitaxel-stabilized MTs coated with distinct Tau isoforms by synchrotron small-angle X-ray scattering (SAXS) of MT-Tau mixtures under osmotic pressure (P). In going from bare MTs to MTs with Tau coverage near the physiological submonolayer regime (Tau/tubulin-dimer molar ratio; Φ_Tau = 1/10), isoforms with longer N-terminal tails (NTTs) sterically stabilized MTs, preventing bundling up to P_B ∼ 10,000-20,000 Pa, an order of magnitude larger than bare MTs. Tau with short NTTs showed little additional effect in suppressing the bundling pressure (P_B ∼ 1,000-2,000 Pa) over the same range. Remarkably, the abrupt increase in PB observed for longer isoforms suggests a mushroom to brush transition occurring at 1/13 < Φ_Tau < 1/10, which corresponds to MT-bound Tau with NTTs that are considerably more extended than SAXS data for Tau in solution indicate. Modeling of Tau-mediated MT-MT interactions supports the hypothesis that longer NTTs transition to a polyelectrolyte brush at higher coverages. Higher pressures resulted in isoform-independent irreversible bundling because the polyampholytic nature of Tau leads to short-range attractions. These findings suggest an isoform-dependent biological role for regulation by Tau, with longer isoforms conferring MT steric stabilization against aggregation either with other biomacromolecules or into tight bundles, preventing loss of function in the crowded axon environment.

Tau, intrinsically disordered proteins, microtubule, SAXS, force measurement

¹P.J.C. and M.C.C. contributed equally to this work.

²Present address: Quality and Compliance Department, FusionRx, Los Angeles, CA 90025.

³To whom correspondence should be addressed.

Author contributions: M.C.C., U.R., and C.R.S. designed research; H.P.M. purified tubulin; H.E.F. provided Tau protein isoforms from plasmid preparations; P.J.C., M.C.C., and U.R. performed research; P.J.C., M.C.C., and C.R.S. analyzed data; P.J.C. and C.R.S. modeled data; U.R. provided additional input on the modeled data; P.J.C. and C.R.S. wrote the paper; S.C.F. provided additional writing input; and Y.L. and L.W. provided critical suggestions on presentation of X-ray and optical microscopy data.

논문정보

형식Research article
게재일2015년 11월 (BRIC 등록일 2015-12-24)
연구진국내+국외 연구진
분야 생명과학 > 구조생물 및 생물물리학

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