title: GDP-tubulin incorporation into growing microtubules modulates polymer stability.
abstract: Microtubule growth proceeds through the endwise addition of nucleotide-bound tubulin dimers. The microtubule wall is composed of GDP-tubulin subunits, which are thought to come exclusively from the incorporation of GTP-tubulin complexes at microtubule ends followed by GTP hydrolysis within the polymer. The possibility of a direct GDP-tubulin incorporation into growing polymers is regarded as hardly compatible with recent structural data. Here, we have examined GTP-tubulin and GDP-tubulin incorporation into polymerizing microtubules using a minimal assembly system comprised of nucleotide-bound tubulin dimers, in the absence of free nucleotide. We find that GDP-tubulin complexes can efficiently co-polymerize with GTP-tubulin complexes during microtubule assembly. GDP-tubulin incorporation into microtubules occurs with similar efficiency during bulk microtubule assembly as during microtubule growth from seeds or centrosomes. Microtubules formed from GTP-tubulin/GDP-tubulin mixtures display altered microtubule dynamics, in particular a decreased shrinkage rate, apparently due to intrinsic modifications of the polymer disassembly properties. Thus, although microtubules polymerized from GTP-tubulin/GDP-tubulin mixtures or from homogeneous GTP-tubulin solutions are both composed of GDP-tubulin subunits, they have different dynamic properties, and this may reveal a novel form of microtubule "structural plasticity."
authors.affiliation: Institut National de la Santé et de la Recherche Médicale Unité 836, Institut des Neurosciences de Grenoble, Université Joseph Fourier, 38042 Grenoble, Cedex 9, France. odile.valiron@ujf-grenoble.fr
authors.forename: Odile
authors.initials: O
authors.lastname: Valiron
authors.forename: Isabelle
authors.initials: I
authors.lastname: Arnal
authors.forename: Nicolas
authors.initials: N
authors.lastname: Caudron
authors.forename: Didier
authors.initials: D
authors.lastname: Job
mesh_terms: D000818:Animals; D001671:Biochemistry / Q000379:methods; D018385:Centrosome / Q000378:metabolism; D020285:Cryoelectron Microscopy / Q000379:methods; D019281:Dimerization; D005374:Filtration; D006153:Guanosine Diphosphate / Q000737:chemistry*; D006160:Guanosine Triphosphate / Q000737:chemistry; D006801:Humans; D006868:Hydrolysis; D008870:Microtubules / Q000737:chemistry / Q000378:metabolism*; D009711:Nucleotides / Q000737:chemistry; D011108:Polymers / Q000737:chemistry*; D014404:Tubulin / Q000737:chemistry*; D050257:Tubulin Modulators / Q000737:chemistry
chemical_list: D009711:Nucleotides; D011108:Polymers; D014404:Tubulin; D050257:Tubulin Modulators; D006153:Guanosine Diphosphate; D006160:Guanosine Triphosphate