Agenda
14/01/2015 - 12:00 - Auditori PRBB

The role of end binding proteins and their binding site in microtubule growth and stability


Scientific sessions, CRG Group Leader Seminars

Sebastian Maurer

Cytoskeleton Dependent RNA Distribution Mechanisms Group, Cell and Developmental Biology Programme, CRG



Short Biography

Sebastian Maurer studied Biology at the Phillips University in Marburg and received his PhD in Biochemistry at Jacobs University Bremen. After a Postdoc at EMBL Heidelberg and LRI London, Sebastian established his laboratory at CRG Barcelona in 2014. His current research focuses on understanding principles and function of RNA-cytoskeleton interactions. This includes cytoplasmic transport of coding and non-coding RNAs, coupling of RNA transport and translational regulation and functions of RNA binding proteins in microtubule cytoskeleton organisation.

Abstract

Growing microtubule ends serve as transient binding platforms for essential proteins that regulate microtubule dynamics and interactions with cellular substructures. End Binding proteins (EBs) recruit most of these factors. Using cryo-electron microscopy, subnanometer single particle reconstruction and fluorescence imaging, we present a pseudo-atomic model of how the calponin homology (CH) domain of the fission yeast EB Mal3 binds to the end region of growing microtubules. The Mal3 CH domain bridges protofilaments except at the microtubule seam. By binding close to the exchangeable GTP binding site, the CH domain is ideally positioned to sense the microtubule’s nucleotide state. Strikingly, the microtubule end region that is recognized by EBs is also a stabilizing structural cap protecting the microtubule from depolymerisation. Using a combination of in vitro reconstitution, time-lapse fluorescence microscopy, and sub-pixel-precision image analysis, 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. EB1 binding accelerates conformational maturation in the microtubule, most likely by promoting lateral protofilament interactions and by accelerating reactions of the GTP hydrolysis cycle. The microtubule maturation time is directly linked to the duration of a growth pause just before microtubule depolymerisation, indicating an important role of the maturation time for the control of dynamic instability. These results 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.