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UID:1-196@lptms.universite-paris-saclay.fr
DTSTART:20140131T140000Z
DTEND:20140131T150000Z
DTSTAMP:20140118T183953Z
URL:http://www.lptms.universite-paris-saclay.fr/seminars/physics-biology-i
 nterface-seminar-aurelien-roux/
SUMMARY:Physics-Biology interface seminar: Aurélien Roux - Moyen Amphi\, B
 uilding 510\, Université Paris-Saclay Orsay - 31 Jan 14 14:00
DESCRIPTION:Role of membrane elasticity in clathrin-mediated endocytosis\nA
 urélien Roux (Université de Genève\, Suisse)\nIn Clathrin-mediated endo
 cytosis\, Clathrin assembles into a soccerball-like structure at the plasm
 a membrane that was proposed to deform the membrane by scaffolding. Howeve
 r\, controversies in the community have appeared on the exact role of Clat
 hrin: does its polymerization force is sufficient to curve the membrane\, 
 or deformation by other means (protein insertion) is required? We studied 
 the formation of Clathrin buds from Giant Unilamellar Vesicles\, and found
  that the pits can be flattened when membrane tension is increased. This s
 uggested that the Clathrin polymerization force could be counteracted by m
 embrane tension\, which we further proved by directly measuring Clathrin p
 olymerization force: by pulling a membrane tube out of a GUV aspirated in 
 a micropipette\, we can measure the force required to hold the tube throug
 h an optical tweezer system. When Clathrin is added\, it polymerizes onto 
 the GUV predominantly\, and the force drops. From these measurements\, we 
 can deduce that the polymerization strength of Clathrin is in the range of
  a few hundred micronewtons per meter. This value confirms that clathrin p
 olymerization can be counteracted efficiently by membrane tension. \nTo fi
 nalize endocytosis\, the clathrin-bud needs to be separated from the plasm
 a membrane. Membrane fission requires the constriction and breakage of a t
 ransient neck\, splitting one membrane compartment into two. The GTPase Dy
 namin forms a helical coat that constricts membrane necks of Clathrin-coat
 ed pits to promote their fission. Dynamin constriction is necessary but no
 t sufficient\, questioning the minimal requirements for fission. Here we s
 how that fission occurs at the edge of the Dynamin coat\, where it is conn
 ected to the uncoated membrane. At this location\, the specific shape of t
 he membrane increases locally its elastic energy\, facilitating fission by
  reducing its energy barrier. We predict that fission kinetics should depe
 nd on tension\, bending rigidity and the Dynamin constriction torque. We v
 erify that fission times depend on membrane tension in controlled conditio
 ns in vitro and in Clathrin-mediated endocytosis in vivo. By numerically e
 stimating the energy barrier from the increased elastic energy\, and measu
 ring the Dynamin torque\, we show that: 1- Dynamin torque\, ≈1nN.nm\, is
  huge but necessary to achieve constriction\, and 2- Dynamin work sufficie
 ntly reduces the energy barrier to promote spontaneous fission. \n
LOCATION:Moyen Amphi\, Building 510\, Université Paris-Saclay Orsay\, 15 R
 ue Georges Clemenceau\, orsay\, France
GEO:48.698187;2.181768
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  orsay\, France;X-APPLE-RADIUS=100;X-TITLE=Moyen Amphi\, Building 510\, Un
 iversité Paris-Saclay Orsay:geo:48.698187,2.181768
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