Binding of the PH and polybasic C-terminal domains of ARNO to phosphoinositides and to acidic lipids.
The activity on ARF of the guanine nucleotide exchange factor ARNO depends on its membrane recruitment, induced by binding of its PH domain to phosphoinositides. A polycationic C-terminal extension to the PH domain might also contribute to its specific binding to phosphatidylinositol 4,5-bisphosphate [(4,5)PIP2] and to phosphatidylinositol 3,4,5-trisphosphate [(3,4,5)PIP3], and to ionic binding to other acidic lipids. We have analyzed in vitro the relative contributions to phospholipid binding of the PH domain and C-terminal extension by cosedimentation of "PH+C domain" and "nominal PH domain" protein constructs including or not including the polycationic C-terminus, with sucrose-loaded unilamellar vesicles made of equal proportions of the neutral lipids phosphatidylcholine and phosphatidylethanolamine, and supplemented or not with 30% acidic phosphatidylserine (PS) and 2% of various phosphoinositides. Binding was measured as a function of the vesicle concentration and of the medium ionic strength. Both proteins bound with higher affinity to (3,4,5)PIP3 than to (4,5)PIP2, the selectivity for (3,4,5)PIP3 being highest for the nominal PH domain. We observed also a clear selectivity of (3,4,5)PIP3 over (4,5)PIP2 for stimulating the activity of ARNO on ARF with vesicles containing 10% PS and 1% PIP2 or PIP3. Our data suggest that the PH domain provides the specific phosphoinositide binding site and some unspecific ionic interaction with acidic PS, whereas the polybasic C domain contributes to binding mainly by unspecific ionic interactions vith PS. Phosphorylation by protein kinase C of a serine in the C domain reduces the ionic affinity of the PH+C domain for PS, but does not affect the phosphoinositide specificity.
Macia
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CNRS, Institut de Pharmacologie Moléculaire et Cellulaire, 660 route des Lucioles, Sophia Antipolis, F-06560 Valbonne, France.
Paris
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Chabre
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D020727:ADP-Ribosylation Factors / Q000737:chemistry; D000595:Amino Acid Sequence; D001792:Blood Platelets / Q000737:chemistry; D001798:Blood Proteins / Q000737:chemistry / Q000378:metabolism*; D002850:Chromatography, Gel; D020690:GTPase-Activating Proteins / Q000737:chemistry / Q000378:metabolism*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008051:Lipid Bilayers / Q000737:chemistry / Q000378:metabolism; D008274:Magnesium / Q000737:chemistry; D008969:Molecular Sequence Data; D019269:Phosphatidylinositol 4,5-Diphosphate / Q000737:chemistry; D018129:Phosphatidylinositol Phosphates / Q000737:chemistry; D010716:Phosphatidylinositols / Q000737:chemistry / Q000378:metabolism*; D010718:Phosphatidylserines / Q000737:chemistry; D010743:Phospholipids / Q000032:analysis / Q000737:chemistry / Q000378:metabolism*; D010750:Phosphoproteins / Q000737:chemistry / Q000378:metabolism*; D010766:Phosphorylation; D011485:Protein Binding; D011493:Protein Kinase C / Q000378:metabolism; D017434:Protein Structure, Tertiary; D017386:Sequence Homology, Amino Acid; D012694:Serine / Q000378:metabolism; D012965:Sodium Chloride / Q000378:metabolism; D014461:Ultracentrifugation
D001798:Blood Proteins; D020690:GTPase-Activating Proteins; D008051:Lipid Bilayers; D019269:Phosphatidylinositol 4,5-Diphosphate; D018129:Phosphatidylinositol Phosphates; D010716:Phosphatidylinositols; D010718:Phosphatidylserines; D010743:Phospholipids; D010750:Phosphoproteins; C102474:cytohesin-2; C060974:phosphatidylinositol 3,4,5-triphosphate; C039077:platelet protein P47; D012965:Sodium Chloride; D012694:Serine; D011493:Protein Kinase C; D020727:ADP-Ribosylation Factors; D008274:Magnesium