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VIEWS: 8 PAGES: 63

									Structural Basis for Ligand-
 Receptor Recognition and
       Dimerization


    Moosa Mohammadi
    Dept. of Pharmacology
    Medical Science Building, 4th Floor,
    Rooms 425, 431
    mohammad@saturn.med.nyu.edu
In multicellular organisms, the decision a cell has to make whether to divide, to differentiate or to
  die is controlled by ligands (growth factors, hormones) that circulate outside of the cell. These
  ligands in order to transmit their signals must interact with cell surface receptors that possess
                         enzymatic activity known as protein kinase activity.




                                                                                       Ligands




                                                      kinase
                                Associated           Covalently linked         Plasmamembrane
                                                                                    Barrier


                                       Nucleous
         Single Transmembrane-Spanning Receptors

                                 Ligand

                Receptor




Extracellular




Intracellular
                Mechanisms of Signal Transduction
                        Conformational Change




Extracellular




Intracellular                 GDP
                              GTP   a    
                                         
                Receptor Dimerization




Extracellular


                       Y




                               Y
Intracellular
                           Y


                               Y
                       Y




                               Y
    Early experiments suggesting
       that receptors undergo
            dimerization

•Truncated receptors lacking the cytoplasmic domain
inhibit signaling.
•Antibodies against the cytoplasmic domain activate
the kinase domain.
•Transmembrane helices are interchangeable between
different receptors.
       Antibody-mediated activation




                Receptor




Extracellular




Intracellular
                           Fab



                Receptor




Extracellular




Intracellular
           Growth factor




Receptor                   Ras
              Grb2
                                 Raf
                                       MAPKK
                     Sos                             MAPK




            Shc

                                       Jun     Fos

                                        NUCLEUS
Phenotypes of patients with Apert syndrome
which results from point mutation in
FGF receptor
                 Ligand-Receptor Systems


•Growth Hormone (GH) Receptor

•Erythropoietin (EPO) Receptor


•Bone Morphogenic Protein (BMP) Receptor


•Vascular Endothelial Growth (VEGF) Receptor
•Nerve Growth Factor (NGF) Receptor



•Fibroblast Growth factor (FGF) Receptor
                  Cytokine Receptors



• Large family of single-pass transmembrane receptors.


• Receptors bind polypeptide ligands: mediators of cell
growth, differentiation and immune responses.


• Cytoplasmic domain does not contain intrinsic protein
tyrosine kinase activity - associated with Jak tyrosine
kinases.
Cytokine Receptors
  Activation Through Binding of a Monomeric
           Ligand – Growth Hormone


• GH stimulates the growth and metabolism of muscle, bone
and cartilage cells.


• GH is a member of the 4-helix bundle family.


• The active form of GH is a monomer. Stoichiometry of
binding is 1:2 GH-GHR.
Ribbon Diagram of Growth Hormone
Four-Helix-Bundle Structure
Four-Helix-Bundle is Stabilized by Hydrophobic
      Contacts Between the Four Helices
Ribbon Diagram of Extracellular Domain of
       Growth Hormone Receptor
Fibronectin Type III Domain is a Close Cousin of
    Immunoglobulin Superfamily Domains
Ribbon Diagram of the 1:2 Complex between GH
                  and GHR
                  GH-GHR Complex

GH-GHR contact II: 900 Å2




                                      GH-GHR contact I: 1230 Å2




                            GHR-GHR contact: 500 Å2
Details of GH-GHR Interactions
Ribbon Diagram of the 1:1 Complex Between GH
            and Prolactin Receptor
Hormone-Receptor Interactions Involving the
     Linker Region of the Receptor
Hormone-Receptor Interactions Involving the F-
 G Loop in the C-terminal Fibronectin Domain
  Activation Through Binding of a Monomeric
        Ligand – Erythropoietin (EPO)

• EPO is a haematopoietic cytokine required for
differentiation and proliferation of precursor cells into red
blood cells.


• Like GH, EPO is monomeric and belongs to the 4-helix
bundle family.


• EPO binds to its receptor (EPOR) with a stoichiometry of
1:2 EPO-EPOR.
Epo:EpoR Complex - Dependence on Receptor
              Orientation
RasMol Presentation of the Dimeric EPO-EPOR
                  Structure
Growth Hormone Paradigm
Activation of a Receptor Serine/Threonine Kinase
 – Bone Morphogenic Protein (BMP) Receptor


• Bone morphogenic proteins (BMPs) belong to the
Transforming Growth Factor  (TGF) superfamily of
ligands which includes TGF, activins/Inhibins and GDFs.
• BMPs regulate bone and cartilage formation in adults and
are also involved in central steps in early embryonic
development.
•BMPs are dimeric ligands and have the characteristic
“Cystine Knot “ motif found in other members of TGF
family.
• The receptors for TGF family of ligands are
transmembrane receptors with intrinsic serine/threonine
kinase activity.
                TGF Receptors




                         Cys-rich
Extracellular




Intracellular
                        Ser/Thr kinase
Activation via Dimeric Ligand: BMP-BMPR Structure
RasMol Presentation of the Dimeric BMP-BMPR
                  Structure
              Receptor Tyrosine Kinases



• Large family of single-pass transmembrane receptors.


• Receptors are predominantly for growth factors but also
for insulin.


• Cytoplasmic domain contains intrinsic protein tyrosine
kinase activity.
Receptor Tyrosine Kinase Family
Activation Through Binding of a Dimeric Ligand
     – Vascular Endothelial Growth Factor


• VEGF is a mitogen that is highly specific for endothelial
cells.


• VEGF is a potent angiogenic factor involved in the
development of the vascular system and also in tumor
angiogenesis.


• VEGF is a covalent (disulfide-linked) dimer.
VEGFR Family



        Ig-like
VEGF-Flt1 Dimer
          VEGF-Flt1 Dimer
                      VEGF

                             Flt1-D2


Flt1-D2

             VEGF
VEGF Interacting Residues


Ig domain 2
RasMol Presentation of the Dimeric VEGF-FLT1
                  Structure
Model for Flt1 Dimerization
Activation Through Binding of a Dimeric Ligand
         – Neurotrophic Growth Factor

• NGF is a member of a family of neurotrophins which also
includes brain-derived neurotrophic factor (BDNF), NT-3,
NT-4/5 and NT-6.


• NGF mediates neuronal differentiation and survival.


• These neurotrophins are non-covalent dimers, members of
the cystine knot family.
Trk (NGF Receptor) Family


      Leu-rich      Cys-rich




                 Ig-like
           NGF-Trk Dimer




Domain 5                   Domain 5
 Common and Specific Interaction Sites


      Specificity interface




Common interface
Common and Specific Interaction Sites




                          Specificity interface




Common interface
       Alignment of Neurotrophic Factors and Trk-D5

  Ligands


Common site
Specificity site




  Receptors
RasMol Presentation of the Dimeric NGF-TRK
                 Structure
Dimeric Ligands with “Cystine Knot” Motif




       (BMP-2)
Receptor Dimerization by Dimeric Ligands with
            “Cystine Knot” Motif
Growth Hormone Paradigm
Crystal Structure of Flt3 Ligand;
 Dimer of two 4-helix Bundels
RasMol Presentation of FLT3 Ligand;
   Dimer of two 4-helix Bundles
 Dimerization by Flt3L Versus VEGF


Flt3L-Flt3 (model)    VEGF-Flt1 (partial model)

								
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