The Caenorhabditis elegans septin complex is nonpolar.
Septins are conserved GTPases that form heteromultimeric complexes and assemble into filaments that play a critical role in cell division and polarity. Results from budding and fission yeast indicate that septin complexes form around a tetrameric core. However, the molecular structure of the core and its influence on the polarity of septin complexes and filaments is poorly defined. The septin complex of the nematode Caenorhabditis elegans is formed entirely by the core septins UNC-59 and UNC-61. We show that UNC-59 and UNC-61 form a dimer of coiled-coil-mediated heterodimers. By electron microscopy, this heterotetramer appears as a linear arrangement of four densities representing the four septin subunits. Fusion of GFP to the N termini of UNC-59 and UNC-61 and subsequent electron microscopic visualization suggests that the sequence of septin subunits is UNC-59/UNC-61/UNC-61/UNC-59. Visualization of GFP extensions fused to the extremity of the C-terminal coiled coils indicates that these extend laterally from the heterotetrameric core. Together, our study establishes that the septin core complex is symmetric, and suggests that septins form nonpolar filaments.
John
Corinne M
CM
Institute of Biochemistry, ETH Zürich, Zürich, Switzerland.
Hite
Richard K
RK
Weirich
Christine S
CS
Fitzgerald
Daniel J
DJ
Jawhari
Hatim
H
Faty
Mahamadou
M
Schläpfer
Dominik
D
Kroschewski
Ruth
R
Winkler
Fritz K
FK
Walz
Tom
T
Barral
Yves
Y
Steinmetz
Michel O
MO
D000818:Animals; D017173:Caenorhabditis elegans / Q000378:metabolism*; D029742:Caenorhabditis elegans Proteins / Q000737:chemistry* / Q000378:metabolism* / Q000648:ultrastructure; D018797:Cell Cycle Proteins / Q000737:chemistry / Q000378:metabolism; D002850:Chromatography, Gel; D019281:Dimerization; D019204:GTP-Binding Proteins / Q000737:chemistry / Q000378:metabolism; D057927:Hydrophobic and Hydrophilic Interactions; D007313:Insecta; D008954:Models, Biological; D046912:Multiprotein Complexes / Q000737:chemistry* / Q000378:metabolism* / Q000648:ultrastructure; D020836:Protein Structure, Quaternary; D017433:Protein Structure, Secondary; D021122:Protein Subunits / Q000737:chemistry / Q000378:metabolism; D021381:Protein Transport; D015003:Yeasts
D029742:Caenorhabditis elegans Proteins; D018797:Cell Cycle Proteins; D046912:Multiprotein Complexes; D021122:Protein Subunits; C418245:UNC-59 protein, C elegans; C418244:unc-61 protein, C elegans; D019204:GTP-Binding Proteins