title: EB1 accelerates two conformational transitions important for microtubule maturation and dynamics.
abstract: BACKGROUND
  The dynamic properties of microtubules depend on complex nanoscale structural rearrangements in their end regions. Members of the EB1 and XMAP215 protein families interact autonomously with microtubule ends. EB1 recruits several other proteins to growing microtubule ends and has seemingly antagonistic effects on microtubule dynamics: it induces catastrophes, and it increases growth velocity, as does the polymerase XMAP215.
  
  
  RESULTS
  Using a combination of in vitro reconstitution, time-lapse fluorescence microscopy, and subpixel-precision image analysis and convolved model fitting, we have studied the effects of EB1 on conformational transitions in growing microtubule ends and on the time course of catastrophes. EB1 density distributions at growing microtubule ends reveal two consecutive conformational transitions in the microtubule end region, which have growth-velocity-independent kinetics. EB1 binds to the microtubule after the first and before the second conformational transition has occurred, positioning it several tens of nanometers behind XMAP215, which binds to the extreme microtubule end. EB1 binding accelerates conformational maturation in the microtubule, most likely by promoting lateral protofilament interactions and by accelerating reactions of the guanosine triphosphate (GTP) hydrolysis cycle. The microtubule maturation time is directly linked to the duration of a growth pause just before microtubule depolymerization, indicating an important role of the maturation time for the control of dynamic instability.
  
  
  CONCLUSIONS
  These activities establish EB1 as a microtubule maturation factor and provide a mechanistic explanation for its effects on microtubule growth and catastrophe frequency, which cause microtubules to be more dynamic.
authors: London Research Institute, Cancer Research UK, 44 Lincoln's Inn Fields, London WC2A 3LY, UK.
authors: Sebastian P
authors: SP
authors: Maurer
authors: London Research Institute, Cancer Research UK, 44 Lincoln's Inn Fields, London WC2A 3LY, UK.
authors: Nicholas I
authors: NI
authors: Cade
authors: London Research Institute, Cancer Research UK, 44 Lincoln's Inn Fields, London WC2A 3LY, UK.
authors: Gergő
authors: G
authors: Bohner
authors: London Research Institute, Cancer Research UK, 44 Lincoln's Inn Fields, London WC2A 3LY, UK.
authors: Nils
authors: N
authors: Gustafsson
authors: London Research Institute, Cancer Research UK, 44 Lincoln's Inn Fields, London WC2A 3LY, UK.
authors: Emmanuel
authors: E
authors: Boutant
authors: London Research Institute, Cancer Research UK, 44 Lincoln's Inn Fields, London WC2A 3LY, UK. Electronic address: thomas.surrey@cancer.org.uk.
authors: Thomas
authors: T
authors: Surrey
mesh_terms: D008869:Microtubule-Associated Proteins / Q000737:chemistry / Q000378:metabolism*; D008870:Microtubules / Q000737:chemistry / Q000378:metabolism*; D011485:Protein Binding; D011487:Protein Conformation
chemical_list: D008869:Microtubule-Associated Proteins