STRUCTURAL-CHANGES AT MICROTUBULE ENDS ACCOMPANYING GTP HYDROLYSIS - INFORMATION FROM A SLOWLY HYDROLYZABLE ANALOG OF GTP, GUANYLYL (ALPHA,BETA)METHYLENEDIPHOSPHONATE

Microtubules are dynamic polymers that interconvert between periods of slow growth and fast shrinkage, The energy driving this nonequilibriu m behavior comes from the hydrolysis of GTP, which is required to dest abilize the microtubule lattice, To understand the mechanisnn of this destabilization, cryo-electron microscopy was used to compare the stru cture of the ends of shrinking microtubules assembled in the presence of either GTP or the slowly hydrolyzable analogue guanylyl (alpha,beta ) methylenediphosphonate (GMPCPP), Depolymerization was induced by col d or addition of calcium, With either nucleotide, we have observed cur led oligomers at the ends of shrinking microtubules. However, GDP olig omers were consistently more curved than GMPCPP oligomers, This differ ence in curvature between depolymerizing GDP and GMPCPP protofilaments suggests that GTP hydrolysis is accompanied by an increase in curvatu re of the protofilaments, thereby destabilizing the lateral interactio ns between tubulin subunits in the microtubule lattice.