Analysis of the function of Spire in actin assembly and its synergy with formin and profilin.
The Spire protein, together with the formin Cappuccino and profilin, plays an important role in actin-based processes that establish oocyte polarity. Spire contains a cluster of four actin-binding WH2 domains. It has been shown to nucleate actin filaments and was proposed to remain bound to their pointed ends. Here we show that the multifunctional character of the WH2 domains allows Spire to sequester four G-actin subunits binding cooperatively in a tight SA(4) complex and to nucleate, sever, and cap filaments at their barbed ends. Binding of Spire to barbed ends does not affect the thermodynamics of actin assembly at barbed ends but blocks barbed end growth from profilin-actin. The resulting Spire-induced increase in profilin-actin concentration enhances processive filament assembly by formin. The synergy between Spire and formin is reconstituted in an in vitro motility assay, which provides a functional basis for the genetic interplay between Spire, formin, and profilin in oogenesis.
Cytoskeleton Dynamics and Motility Group, Laboratoire d'Enzymologie et Biochimie Structurales, CNRS, 91198 Gif-sur-Yvette, France.
Montserrat
M
Bosch
Kim Ho Diep
KH
Le
Beata
B
Bugyi
John J
JJ
Correia
Louis
L
Renault
Marie-France
MF
Carlier
D008841:Actin Cytoskeleton / Q000378:metabolism; D000199:Actins / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D001667:Binding, Competitive / Q000187:drug effects; D001681:Biological Assay; D002850:Chromatography, Gel; D005326:Fetal Proteins / Q000378:metabolism*; D005453:Fluorescence; D000080865:Formins; D006801:Humans; D006868:Hydrolysis / Q000187:drug effects; D008840:Microfilament Proteins / Q000737:chemistry / Q000378:metabolism*; D009687:Nuclear Proteins / Q000378:metabolism*; D051304:Profilins / Q000378:metabolism*; D011485:Protein Binding / Q000187:drug effects; D011817:Rabbits; D013947:Thymosin / Q000378:metabolism; D014461:Ultracentrifugation; D000099201:Thymosin beta(4)
D000199:Actins; D000255:Adenosine Triphosphate; D005326:Fetal Proteins; D000080865:Formins; D008840:Microfilament Proteins; D009687:Nuclear Proteins; D051304:Profilins; D013947:Thymosin; D000099201:Thymosin beta(4); C000592292:SPIRE1 protein, human