title: Non-canonical interaction of phosphoinositides with pleckstrin homology domains of Tiam1 and ArhGAP9.
abstract: Pleckstrin homology (PH) domains are phosphoinositide (PI)-binding modules that target proteins to membrane surfaces. Here we define a family of PH domain proteins, including Tiam1 and ArhGAP9, that demonstrates specificity for PI(4,5)P(2), as well as for PI(3,4,5)P(3) and PI(3,4)P(2), the products of PI 3-kinase. These PH domain family members utilize a non-canonical phosphoinositide binding pocket related to that employed by beta-spectrin. Crystal structures of the PH domain of ArhGAP9 in complex with the headgroups of Ins(1,3,4)P(3), Ins(1,4,5)P(3), and Ins(1,3,5)P(3) reveal how two adjacent phosphate positions in PI(3,4)P(2), PI(4,5)P(2), and PI(3,4,5)P(3) are accommodated through flipped conformations of the bound phospholipid. We validate the non-canonical site of phosphoinositide interaction by showing that binding pocket mutations, which disrupt phosphoinositide binding in vitro, also disrupt membrane localization of Tiam1 in cells. We posit that the diversity in PI interaction modes displayed by PH domains contributes to their versatility of use in biological systems.
authors.affiliation: Program in Systems Biology, Samuel Lunenfeld Research Institute, Mount Sinai Hospital, Toronto, Ontario M5G 1X5.
authors.forename: Derek F J
authors.initials: DF
authors.lastname: Ceccarelli
authors.forename: Ivan M
authors.initials: IM
authors.lastname: Blasutig
authors.forename: Marilyn
authors.initials: M
authors.lastname: Goudreault
authors.forename: Zhiqin
authors.initials: Z
authors.lastname: Li
authors.forename: Julie
authors.initials: J
authors.lastname: Ruston
authors.forename: Tony
authors.initials: T
authors.lastname: Pawson
authors.forename: Frank
authors.initials: F
authors.lastname: Sicheri
mesh_terms: D000818:Animals; D001665:Binding Sites / Q000235:genetics; D002462:Cell Membrane / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D018360:Crystallography, X-Ray; D020690:GTPase-Activating Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D020662:Guanine Nucleotide Exchange Factors / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D006801:Humans; D008565:Membrane Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D051379:Mice; D008958:Models, Molecular; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010716:Phosphatidylinositols / Q000737:chemistry* / Q000378:metabolism; D011485:Protein Binding / Q000235:genetics; D017434:Protein Structure, Tertiary / Q000235:genetics; D000075684:T-Lymphoma Invasion and Metastasis-inducing Protein 1
chemical_list: C431580:ARHGAP9 protein, human; D020690:GTPase-Activating Proteins; D020662:Guanine Nucleotide Exchange Factors; D008565:Membrane Proteins; D010716:Phosphatidylinositols; D000075684:T-Lymphoma Invasion and Metastasis-inducing Protein 1; C513260:Tiam1 protein, mouse; D019869:Phosphatidylinositol 3-Kinases