title: The SH3 domain of Caskin1 binds to lysophosphatidic acid suggesting a direct role for the lipid in intracellular signaling.
abstract: Src homology 3 or SH3 domains constitute one of the most common protein domains in signal transduction, generally characterized by their binding to proline-rich sequences on interacting signaling proteins. Caskin1, a scaffold protein regulating cortical actin filaments, enriched in neural synapses in mammals, has an atypical SH3 domain. Key aromatic residues necessary for ligand binding that are present in canonical SH3 domains are missing from Caskin1 SH3. In concordance, proline-rich interacting partner could not be identified yet. Based on previous reports that several SH3 domains are able to bind phospholipids, we sought for lipid interacting partners of the SH3 domain of human Caskin1. We investigated the signaling-born lysophospholipid mediators, such as lysophosphatidic acid (LPA) and sphingosine-1-phosphate (S1P) as potential binding partners for this SH3 domain. These lipid mediators as first messengers activate G protein-coupled receptors. They also exert several G protein-coupled receptor-independent functions but their intracellular target proteins are mostly unknown. Here we provide evidence that the SH3 domain of human Caskin1 selectively binds to LPA in vitro. The binding strength and stoichiometry depend on the association-state of the lipid, with nanomolar affinity to LPA-containing membraneous surfaces. The amino acids involved in the interaction are located in a β-strand structure and are distinct from those corresponding to the canonical proline-rich ligand-binding groove in the SH3 domain of Src kinase. Our results suggest that the SH3 domain of human Caskin1 is a lipid-binding domain rather than a proline-rich motif interacting domain.
authors.affiliation: Institute of Enzymology, Research Centre for Natural Sciences, Hungarian Academy of Sciences, Magyar Tudósok krt 2, Budapest, H-1117, Hungary. Electronic address: koprivanacz.kitti@ttk.mta.hu.
authors.forename: Kitti
authors.initials: K
authors.lastname: Koprivanacz
authors.affiliation: Institute of Organic Chemistry, Research Centre for Natural Sciences, Hungarian Academy of Sciences, Magyar Tudósok krt 2, Budapest, H-1117, Hungary. Electronic address: toke.orsolya@ttk.mta.hu.
authors.forename: Orsolya
authors.initials: O
authors.lastname: Tőke
authors.affiliation: Institute of Enzymology, Research Centre for Natural Sciences, Hungarian Academy of Sciences, Magyar Tudósok krt 2, Budapest, H-1117, Hungary. Electronic address: besztercei.balazs@ttk.mta.hu.
authors.forename: Balázs
authors.initials: B
authors.lastname: Besztercei
authors.affiliation: Institute of Enzymology, Research Centre for Natural Sciences, Hungarian Academy of Sciences, Magyar Tudósok krt 2, Budapest, H-1117, Hungary. Electronic address: juhasz.tunde@ttk.mta.hu.
authors.forename: Tünde
authors.initials: T
authors.lastname: Juhász
authors.affiliation: Institute of Enzymology, Research Centre for Natural Sciences, Hungarian Academy of Sciences, Magyar Tudósok krt 2, Budapest, H-1117, Hungary. Electronic address: radnai.laszlo@ttk.mta.hu.
authors.forename: László
authors.initials: L
authors.lastname: Radnai
authors.affiliation: Institute of Enzymology, Research Centre for Natural Sciences, Hungarian Academy of Sciences, Magyar Tudósok krt 2, Budapest, H-1117, Hungary. Electronic address: mero.balazs@ttk.mta.hu.
authors.forename: Balázs
authors.initials: B
authors.lastname: Merő
authors.affiliation: Institute of Materials and Environmental Chemistry, Research Centre for Natural Sciences, Hungarian Academy of Sciences, Magyar Tudósok krt 2, Budapest, H-1117, Hungary. Electronic address: mihaly.judith@ttk.mta.hu.
authors.forename: Judith
authors.initials: J
authors.lastname: Mihály
authors.affiliation: Institute of Biochemistry, Biological Research Centre, Hungarian Academy of Sciences, Temesvári krt. 62, Szeged, H-6726, Hungary. Electronic address: peter.maria@brc.mta.hu.
authors.forename: Mária
authors.initials: M
authors.lastname: Péter
authors.affiliation: Institute of Biochemistry, Biological Research Centre, Hungarian Academy of Sciences, Temesvári krt. 62, Szeged, H-6726, Hungary. Electronic address: balogh.gabor@brc.mta.hu.
authors.forename: Gábor
authors.initials: G
authors.lastname: Balogh
authors.affiliation: Institute of Biochemistry, Biological Research Centre, Hungarian Academy of Sciences, Temesvári krt. 62, Szeged, H-6726, Hungary. Electronic address: vigh.laszlo@brc.mta.hu.
authors.forename: László
authors.initials: L
authors.lastname: Vígh
authors.affiliation: Institute of Enzymology, Research Centre for Natural Sciences, Hungarian Academy of Sciences, Magyar Tudósok krt 2, Budapest, H-1117, Hungary; Department of Medical Chemistry, Semmelweis University Medical School, Tűzoltó u 37-47, Budapest, H-1094, Hungary. Electronic address: buday.laszlo@ttk.mta.hu.
authors.forename: László
authors.initials: L
authors.lastname: Buday
authors.affiliation: Institute of Enzymology, Research Centre for Natural Sciences, Hungarian Academy of Sciences, Magyar Tudósok krt 2, Budapest, H-1117, Hungary; Department of Biophysics and Radiation Biology, Semmelweis University Medical School, Tűzoltó u 37-47, Budapest, H-1094, Hungary. Electronic address: liliom.karoly@ttk.mta.hu.
authors.forename: Károly
authors.initials: K
authors.lastname: Liliom
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000737:chemistry* / Q000378:metabolism*; D006801:Humans; D042541:Intracellular Space / Q000378:metabolism*; D008024:Ligands; D008055:Lipids / Q000737:chemistry*; D008246:Lysophospholipids / Q000378:metabolism*; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D009419:Nerve Tissue Proteins / Q000737:chemistry* / Q000378:metabolism*; D011392:Proline / Q000378:metabolism; D011485:Protein Binding; D015398:Signal Transduction; D017550:Spectroscopy, Fourier Transform Infrared; D013329:Structure-Activity Relationship; D018909:src Homology Domains
chemical_list: D048868:Adaptor Proteins, Signal Transducing; C473247:CASKIN1 protein, human; D008024:Ligands; D008055:Lipids; D008246:Lysophospholipids; D009419:Nerve Tissue Proteins; D011392:Proline; C032881:lysophosphatidic acid
keywords: Caskin1; SH3 domain; lipid signaling; lysophosphatidic acid; proline-rich motif; protein-lipid interaction