Phosphatidylinositol polyphosphate binding to the mammalian septin H5 is modulated by GTP.
BACKGROUND
Septins are members of a conserved family of GTPases found in organisms as diverse as budding yeast and mammals. In budding yeast, septins form hetero-oligomeric filaments that lie adjacent to the membrane at the mother-bud neck, whereas in mammals, they concentrate at the cleavage furrow of mitotic cells; in both cases, septins provide a required function for cytokinesis. What directs the location and determines the stability of septin filaments, however, remains unknown.


RESULTS
Here we show that the mammalian septin H5 is associated with the plasma membrane and specifically binds the phospholipids phosphatidylinositol 4, 5-bisphosphate (PtdIns(4,5)P(2)) and phosphatidylinositol 3,4, 5-trisphosphate (PtdIns(3,4,5)P(3)). Deletion analysis revealed that this binding occurs at a site rich in basic residues that is conserved in most septins and is located adjacent to the GTP-binding motif. Phosphoinositide binding was inhibited by mutations within this motif and was also blocked by agents known to associate with PtdInsP(2) or by a peptide corresponding to the predicted PtdInsP(2)-binding sequence of H5. GTP binding and hydrolysis by H5 significantly reduced its PtdInsP(2)-binding capability. Treatment of cells with agents that occluded, dephosphorylated or degraded PtdInsP(2) altered the appearance and localization of H5.


CONCLUSIONS
These results indicate that the interaction of septins with PtdInsP(2) might be an important cellular mechanism for the spatial and temporal control of septin accumulation.
Zhang
J
J
Program in Cell Biology, Department of Biochemistry, Hospital for Sick Children, University of Toronto, Toronto, M5G 1X8, Canada.
Kong
C
C
Xie
H
H
McPherson
P S
PS
Grinstein
S
S
Trimble
W S
WS
D016475:3T3 Cells; D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites / Q000235:genetics; D003598:Cytoskeletal Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D020558:GTP Phosphohydrolases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D006160:Guanosine Triphosphate / Q000378:metabolism*; D015759:Ionomycin / Q000494:pharmacology; D051379:Mice; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009355:Neomycin / Q000494:pharmacology; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000378:metabolism; D019269:Phosphatidylinositol 4,5-Diphosphate / Q000378:metabolism*; D018129:Phosphatidylinositol Phosphates / Q000378:metabolism*; D010744:Phosphoric Monoester Hydrolases / Q000235:genetics / Q000378:metabolism; D011485:Protein Binding; D058112:Septins; D017386:Sequence Homology, Amino Acid
D003598:Cytoskeletal Proteins; D009419:Nerve Tissue Proteins; D019269:Phosphatidylinositol 4,5-Diphosphate; D018129:Phosphatidylinositol Phosphates; C060974:phosphatidylinositol 3,4,5-triphosphate; D015759:Ionomycin; D006160:Guanosine Triphosphate; C097702:synaptojanin; D010744:Phosphoric Monoester Hydrolases; D020558:GTP Phosphohydrolases; C115474:Sept4 protein, mouse; D058112:Septins; D009355:Neomycin