title: Centriolar CPAP/SAS-4 Imparts Slow Processive Microtubule Growth.
abstract: Centrioles are fundamental and evolutionarily conserved microtubule-based organelles whose assembly is characterized by microtubule growth rates that are orders of magnitude slower than those of cytoplasmic microtubules. Several centriolar proteins can interact with tubulin or microtubules, but how they ensure the exceptionally slow growth of centriolar microtubules has remained mysterious. Here, we bring together crystallographic, biophysical, and reconstitution assays to demonstrate that the human centriolar protein CPAP (SAS-4 in worms and flies) binds and "caps" microtubule plus ends by associating with a site of β-tubulin engaged in longitudinal tubulin-tubulin interactions. Strikingly, we uncover that CPAP activity dampens microtubule growth and stabilizes microtubules by inhibiting catastrophes and promoting rescues. We further establish that the capping function of CPAP is important to limit growth of centriolar microtubules in cells. Our results suggest that CPAP acts as a molecular lid that ensures slow assembly of centriolar microtubules and, thereby, contributes to organelle length control.
authors.affiliation: Laboratory of Biomolecular Research, Department of Biology and Chemistry, Paul Scherrer Institut, 5232 Villigen PSI, Switzerland.
authors.forename: Ashwani
authors.initials: A
authors.lastname: Sharma
authors.affiliation: Cell Biology, Faculty of Science, Utrecht University, 3584 CH Utrecht, The Netherlands.
authors.forename: Amol
authors.initials: A
authors.lastname: Aher
authors.affiliation: Swiss Institute for Experimental Cancer Research (ISREC), School of Life Sciences, Swiss Federal Institute of Technology (EPFL), 1015 Lausanne, Switzerland.
authors.forename: Nicola J
authors.initials: NJ
authors.lastname: Dynes
authors.affiliation: Laboratory of Biomolecular Research, Department of Biology and Chemistry, Paul Scherrer Institut, 5232 Villigen PSI, Switzerland.
authors.forename: Daniel
authors.initials: D
authors.lastname: Frey
authors.affiliation: Cell Biology, Faculty of Science, Utrecht University, 3584 CH Utrecht, The Netherlands.
authors.forename: Eugene A
authors.initials: EA
authors.lastname: Katrukha
authors.affiliation: Laboratory of Biomolecular Research, Department of Biology and Chemistry, Paul Scherrer Institut, 5232 Villigen PSI, Switzerland.
authors.forename: Rolf
authors.initials: R
authors.lastname: Jaussi
authors.affiliation: Cell Biology, Faculty of Science, Utrecht University, 3584 CH Utrecht, The Netherlands.
authors.forename: Ilya
authors.initials: I
authors.lastname: Grigoriev
authors.affiliation: Bio-EM Facility, School of Life Sciences, Swiss Federal Institute of Technology (EPFL), 1015 Lausanne, Switzerland.
authors.forename: Marie
authors.initials: M
authors.lastname: Croisier
authors.affiliation: Laboratory of Biomolecular Research, Department of Biology and Chemistry, Paul Scherrer Institut, 5232 Villigen PSI, Switzerland.
authors.forename: Richard A
authors.initials: RA
authors.lastname: Kammerer
authors.affiliation: Cell Biology, Faculty of Science, Utrecht University, 3584 CH Utrecht, The Netherlands. Electronic address: a.akhmanova@uu.nl.
authors.forename: Anna
authors.initials: A
authors.lastname: Akhmanova
authors.affiliation: Swiss Institute for Experimental Cancer Research (ISREC), School of Life Sciences, Swiss Federal Institute of Technology (EPFL), 1015 Lausanne, Switzerland. Electronic address: pierre.gonczy@epfl.ch.
authors.forename: Pierre
authors.initials: P
authors.lastname: Gönczy
authors.affiliation: Laboratory of Biomolecular Research, Department of Biology and Chemistry, Paul Scherrer Institut, 5232 Villigen PSI, Switzerland. Electronic address: michel.steinmetz@psi.ch.
authors.forename: Michel O
authors.initials: MO
authors.lastname: Steinmetz
mesh_terms: D000595:Amino Acid Sequence; D045744:Cell Line, Tumor; D002502:Centrioles / Q000378:metabolism* / Q000648:ultrastructure; D018360:Crystallography, X-Ray; D006801:Humans; D008869:Microtubule-Associated Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008870:Microtubules / Q000378:metabolism* / Q000648:ultrastructure; D008958:Models, Molecular; D011485:Protein Binding; D000072417:Protein Domains; D013329:Structure-Activity Relationship; D014404:Tubulin / Q000737:chemistry / Q000378:metabolism
chemical_list: C414735:CENPJ protein, human; D008869:Microtubule-Associated Proteins; D014404:Tubulin
keywords: CPAP/SAS-4; Centrioles; X-ray crystallography; human cells; in vitro reconstitutions; microtubules