RESUMO
The Notch pathway is a core cell-cell signaling system in metazoan organisms with key roles in cell-fate determination, stem cell maintenance, immune system activation, and angiogenesis. Signals are initiated by extracellular interactions of the Notch receptor with Delta/Serrate/Lag-2 (DSL) ligands, whose structure is highly conserved throughout evolution. To date, no structure or activity has been associated with the extreme N termini of the ligands, even though numerous mutations in this region of Jagged-1 ligand lead to human disease. Here, we demonstrate that the N terminus of human Jagged-1 is a C2 phospholipid recognition domain that binds phospholipid bilayers in a calcium-dependent fashion. Furthermore, we show that this activity is shared by a member of the other class of Notch ligands, human Delta-like-1, and the evolutionary distant Drosophila Serrate. Targeted mutagenesis of Jagged-1 C2 domain residues implicated in calcium-dependent phospholipid binding leaves Notch interactions intact but can reduce Notch activation. These results reveal an important and previously unsuspected role for phospholipid recognition in control of this key signaling system.
Assuntos
Proteínas de Ligação ao Cálcio/metabolismo , Proteínas de Ligação a Ácido Graxo/metabolismo , Peptídeos e Proteínas de Sinalização Intercelular/metabolismo , Proteínas de Membrana/metabolismo , Sequência de Aminoácidos , Cálcio/química , Proteínas de Ligação ao Cálcio/genética , Proteínas de Ligação ao Cálcio/ultraestrutura , Diferenciação Celular/genética , Linhagem Celular , Cristalografia por Raios X , Proteínas de Drosophila , Ativação Enzimática/genética , Proteínas de Ligação a Ácido Graxo/ultraestrutura , Células HEK293 , Humanos , Peptídeos e Proteínas de Sinalização Intercelular/genética , Proteína Jagged-1 , Proteínas de Membrana/genética , Proteínas de Membrana/ultraestrutura , Dados de Sequência Molecular , Fosfolipídeos/metabolismo , Estrutura Terciária de Proteína , Receptores Notch/metabolismo , Alinhamento de Sequência , Proteínas Serrate-Jagged , Transdução de Sinais/genéticaRESUMO
The Notch receptor is part of a core signalling pathway which is highly conserved in all metazoan species. It is required for various cell fate decisions at multiple stages of development and in the adult organism, with dysregulation of the pathway associated with genetic and acquired diseases including cancer. Although cellular and in vivo studies have provided considerable insight into the downstream consequences of Notch signalling, relatively little is known about the molecular basis of the receptor/ligand interaction and initial stages of activation. Recent advances in structure determination of the extracellular regions of human Notch-1 and one of its ligands Jagged-1 have given new insights into docking events occurring at the cell surface which may facilitate the development of new highly specific therapies. We review the structural data available for receptor and ligands and identify the challenges ahead.
Assuntos
Receptores Notch/química , Motivos de Aminoácidos , Animais , Sítios de Ligação , Proteínas de Ligação ao Cálcio/química , Proteínas de Ligação ao Cálcio/genética , Comunicação Celular , Humanos , Peptídeos e Proteínas de Sinalização Intercelular/química , Peptídeos e Proteínas de Sinalização Intercelular/genética , Proteína Jagged-1 , Proteínas de Membrana/química , Proteínas de Membrana/genética , Mutação , Ligação Proteica , Estrutura Terciária de Proteína , Receptores Notch/genética , Proteínas Serrate-Jagged , Transdução de SinaisRESUMO
Vitronectin is a multi-functional protein found predominantly as a monomer in blood and as an oligomer in the extracellular matrix. We have dissected the minimal regions of vitronectin protein needed for effective integrin dependent cell adhesion and spreading. A fragment of vitronectin containing the RGD integrin binding site showed similar binding affinity as that of full vitronectin protein to purified integrin alphavbeta3 but had diminished cell adhesion and spreading function in vivo. We demonstrate that the oligomeric state of the protein is responsible for this effect. We provide compelling evidence for the involvement of the heparin binding domain of vitronectin in the oligomerization process and show that such oligomerization reinforces the activity of vitronectin in cell adhesion and spreading.
