Fig. 4: Septin filaments bind lipid with the C-terminal face and pair on the N-terminal face.
From: The hierarchical assembly of septins revealed by high-speed AFM
a Wild-type septin filaments periodically recruit small lipid clusters on one side of individual septin filaments (white arrowhead), and on both outer faces of paired filaments (yellow arrowheads). Occasionally, these lipid clusters fused on the surface (center of the image). b Septin filaments with C-terminal deletion mutants Cdc11-ΔCTE, Cdc12-ΔCTE or Cdc3-ΔCTE septins: Only filaments containing Cdc11-ΔCTE recruit lipid clusters, but display slightly diminished pairing. c Distance distribution between lipid clusters recruited by wild-type septins (~32 nm), and Cdc11-ΔCTE (~20 nm). d Filament alignment (triangles) and pairing (circles) containing Cdc11-ΔCTE (black), Cdc12-ΔCTE (green) and Cdc3-ΔCTE (yellow), compared to wild-type filaments. Data are presented as mean ± s.d. from ≥ 3 different experiments. e Structural model of the yeast septin hetero-octamer rod generated by aligning of the crystal structure of Cdc11 (PDB: 5AR1), and models of Cdc12, Cdc3, and Cdc10 to the crystal structures of in the human hetero-hexamer rod septin-9 (PDB ID: 5CYP), septin-7 (PDB ID: 2QAG), and septin-3 (PDB ID: 4Z54). Boxes display N- and C-terminal sequences, respective (arrows indicate where C-termini protrude from α6 of the respective subunits). The bold numbers indicate the net charges of the surface exposed structurally unresolved termini. Bottom: Schematic of the charge distribution along a septin filament.
