title: A tethered delivery mechanism explains the catalytic action of a microtubule polymerase.
abstract: Stu2p/XMAP215 proteins are essential microtubule polymerases that use multiple αβ-tubulin-interacting TOG domains to bind microtubule plus ends and catalyze fast microtubule growth. We report here the structure of the TOG2 domain from Stu2p bound to yeast αβ-tubulin. Like TOG1, TOG2 binds selectively to a fully 'curved' conformation of αβ-tubulin, incompatible with a microtubule lattice. We also show that TOG1-TOG2 binds non-cooperatively to two αβ-tubulins. Preferential interactions between TOGs and fully curved αβ-tubulin that cannot exist elsewhere in the microtubule explain how these polymerases localize to the extreme microtubule end. We propose that these polymerases promote elongation because their linked TOG domains concentrate unpolymerized αβ-tubulin near curved subunits already bound at the microtubule end. This tethering model can explain catalyst-like behavior and also predicts that the polymerase action changes the configuration of the microtubule end.
authors.affiliation: Department of Biophysics, UT Southwestern Medical Center, Dallas, United States Department of Biochemistry, UT Southwestern Medical Center, Dallas, United States.
authors.forename: Pelin
authors.initials: P
authors.lastname: Ayaz
authors.affiliation: Department of Biophysics, UT Southwestern Medical Center, Dallas, United States Department of Biochemistry, UT Southwestern Medical Center, Dallas, United States.
authors.forename: Sarah
authors.initials: S
authors.lastname: Munyoki
authors.affiliation: Department of Biophysics, UT Southwestern Medical Center, Dallas, United States Department of Biochemistry, UT Southwestern Medical Center, Dallas, United States.
authors.forename: Elisabeth A
authors.initials: EA
authors.lastname: Geyer
authors.affiliation: Department of Biophysics, UT Southwestern Medical Center, Dallas, United States Department of Biochemistry, UT Southwestern Medical Center, Dallas, United States.
authors.forename: Felipe-Andrés
authors.initials: FA
authors.lastname: Piedra
authors.affiliation: Department of Biophysics, UT Southwestern Medical Center, Dallas, United States Department of Biochemistry, UT Southwestern Medical Center, Dallas, United States.
authors.forename: Emily S
authors.initials: ES
authors.lastname: Vu
authors.affiliation: Department of Biophysics, UT Southwestern Medical Center, Dallas, United States Department of Biochemistry, UT Southwestern Medical Center, Dallas, United States.
authors.forename: Raquel
authors.initials: R
authors.lastname: Bromberg
authors.affiliation: Department of Biophysics, UT Southwestern Medical Center, Dallas, United States Department of Biochemistry, UT Southwestern Medical Center, Dallas, United States.
authors.forename: Zbyszek
authors.initials: Z
authors.lastname: Otwinowski
authors.affiliation: Department of Biophysics, UT Southwestern Medical Center, Dallas, United States Department of Biochemistry, UT Southwestern Medical Center, Dallas, United States Howard Hughes Medical Institute, UT Southwestern Medical Center, Dallas, United States.
authors.forename: Nick V
authors.initials: NV
authors.lastname: Grishin
authors.affiliation: Department of Biophysics, UT Southwestern Medical Center, Dallas, United States.
authors.forename: Chad A
authors.initials: CA
authors.lastname: Brautigam
authors.affiliation: Department of Biophysics, UT Southwestern Medical Center, Dallas, United States Department of Biochemistry, UT Southwestern Medical Center, Dallas, United States Luke.Rice@UTSouthwestern.edu.
authors.forename: Luke M
authors.initials: LM
authors.lastname: Rice
mesh_terms: D000818:Animals; D017173:Caenorhabditis elegans / Q000235:genetics / Q000378:metabolism; D029742:Caenorhabditis elegans Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D020134:Catalytic Domain; D005816:Genetic Complementation Test; D008869:Microtubule-Associated Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D008870:Microtubules / Q000737:chemistry* / Q000378:metabolism; D008958:Models, Molecular; D011485:Protein Binding; D054730:Protein Interaction Domains and Motifs; D020033:Protein Isoforms / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D017433:Protein Structure, Secondary; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000201:enzymology / Q000235:genetics*; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D014404:Tubulin / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D029867:Xenopus Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D014982:Xenopus laevis / Q000235:genetics / Q000378:metabolism
chemical_list: C486738:CKAP5 protein, Xenopus; D029742:Caenorhabditis elegans Proteins; D008869:Microtubule-Associated Proteins; D020033:Protein Isoforms; D011994:Recombinant Proteins; C109414:STU2 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D014404:Tubulin; D029867:Xenopus Proteins
keywords: TOG domain; X-ray structure; conformation-selective; kinetic simulation; microtubule
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