title: Magnesium requirements for guanosine 5'-O-(3-thiotriphosphate) induced assembly of microtubule protein and tubulin.
abstract: Two conflicting interpretations on the role of guanosine 5'-O-(3-thiotriphosphate) (GTP gamma S) in microtubule protein and tubulin assembly have been previously reported. One study finds that GTP gamma S promotes assembly while another study reports that GTP gamma S is a potent inhibitor of microtubule assembly. We have examined the potential role of Mg2+ to learn if the conflicting interpretations are due to a metal effect. Turbidity, electron microscopy, and nucleotide binding and hydrolysis were used to analyze the effect of the Mg2+ concentration on GTP gamma S-induced assembly of microtubule protein (tubulin + microtubule-associated proteins) in the presence of buffer +/- 30% glycerol and in buffer with GTP added before or after GTP gamma S. GTP gamma S substantially lowers the Mg2+ concentration required to induce cross-linked or clustered rings of tubulin. These cross-linked rings do not assemble well into microtubules, and GTP only partially restores microtubule assembly. However, taxol will promote GTP gamma S-induced cross-linked rings of microtubule protein to assemble into microtubules. The effect of GTP gamma S on microtubule protein assembly in the presence of Zn2+ with and without added Mg2+ suggests that GTP gamma S also effects the formation of Zn2+-induced sheet aggregates. Purified tubulin was used in assembly experiments with Mg2+, Zn2+, and taxol to better understand GTP gamma S interactions with tubulin. The optimal Mg2+ concentration for assembly of tubulin is lower with GTP gamma S than with GTP.(ABSTRACT TRUNCATED AT 250 WORDS)
mesh_terms: D000818:Animals; D001921:Brain / Q000378:metabolism; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D006160:Guanosine Triphosphate / Q000031:analogs & derivatives* / Q000494:pharmacology; D007700:Kinetics; D046911:Macromolecular Substances; D008274:Magnesium / Q000494:pharmacology*; D008854:Microscopy, Electron; D008870:Microtubules / Q000378:metabolism* / Q000648:ultrastructure*; D013552:Swine; D013873:Thionucleotides / Q000494:pharmacology*; D014404:Tubulin / Q000378:metabolism*; D015032:Zinc / Q000494:pharmacology
chemical_list: D046911:Macromolecular Substances; D013873:Thionucleotides; D014404:Tubulin; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D006160:Guanosine Triphosphate; D008274:Magnesium; D015032:Zinc