title: Crystal structure of Lamellipodin implicates diverse functions in actin polymerization and Ras signaling.
abstract: The adapter protein Lamellipodin (Lpd) plays an important role in cell migration. In particular, Lpd mediates lamellipodia formation by regulating actin dynamics via interacting with Ena/VASP proteins. Its RA-PH tandem domain configuration suggests that like its paralog RIAM, Lpd may also mediate particular Ras GTPase signaling. We determined the crystal structures of the Lpd RA-PH domains alone and with an N-terminal coiled-coil region (cc-RA-PH). These structures reveal that apart from the anticipated coiled-coil interaction, Lpd may also oligomerize through a second intermolecular contact site. We then validated both oligomerization interfaces in solution by mutagenesis. A fluorescence-polarization study demonstrated that Lpd binds phosphoinositol with low affinity. Based on our crystallographic and biochemical data, we propose that Lpd and RIAM serve diverse functions: Lpd plays a predominant role in regulating actin polymerization, and its function in mediating Ras GTPase signaling is largely suppressed compared to RIAM.
authors.affiliation: Department of Developmental Therapeutics, Fox Chase Cancer Center, 333 Cottman Avenue, Philadelphia, PA 19111, USA.
authors.forename: Yu-Chung
authors.initials: YC
authors.lastname: Chang
authors.forename: Hao
authors.initials: H
authors.lastname: Zhang
authors.forename: Mark L
authors.initials: ML
authors.lastname: Brennan
authors.forename: Jinhua
authors.initials: J
authors.lastname: Wu
mesh_terms: D000199:Actins / Q000378:metabolism*; D000595:Amino Acid Sequence; D001665:Binding Sites; D002352:Carrier Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D018360:Crystallography, X-Ray; D006801:Humans; D008565:Membrane Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D016296:Mutagenesis; D010716:Phosphatidylinositols / Q000378:metabolism; D058105:Polymerization; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000737:chemistry / Q000235:genetics; D015398:Signal Transduction; D018631:ras Proteins / Q000378:metabolism*
chemical_list: D000199:Actins; D002352:Carrier Proteins; D008565:Membrane Proteins; D010716:Phosphatidylinositols; C493339:RAPH1 protein, human; D011994:Recombinant Proteins; D018631:ras Proteins