TI - Dynamic interplay between nitration and phosphorylation of tubulin cofactor B in the control of microtubule dynamics . AB - Tubulin cofactor B ( TCoB ) plays an important role in microtubule dynamics by facilitating the dimerization of alpha- and beta- tubulin . Recent evidence suggests that p21-activated kinase 1 ( Pak1 ) , a major signaling nodule in eukaryotic cells , phosphorylates TCoB on Ser-65 and Ser-128 and plays an essential role in microtubule regrowth . However , to date , no upstream signaling molecules have been identified to antagonize the functions of TCoB , which might help in maintaining the equilibrium of microtubules . Here , we discovered that TCoB is efficiently nitrated , mainly on Tyr-64 and Tyr-98 , and nitrated-TCoB attenuates the synthesis of new microtubules . In addition , we found that nitration of TCoB antagonizes signaling -dependent phosphorylation of TCoB , whereas optimal nitration of TCoB requires the presence of functional Pak1 phosphorylation sites , thus providing a feedback mechanism to regulate phosphorylation -dependent MT regrowth . Together these findings identified TCoB as the third cytoskeleton protein to be nitrated and suggest a previously undescribed mechanism , whereby growth factor signaling may coordinately integrate nitric oxide signaling in the regulation of microtubule dynamics .