Structural Basis for LigandReceptor 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
Nucleous
Covalently linked
Plasmamembrane
Barrier
Single Transmembrane-Spanning Receptors
Ligand
Receptor
Extracellular
Intracellular
Mechanisms of Signal Transduction
Conformational Change
Extracellular
Intracellular
GTP
GDP
a


Receptor Dimerization
Extracellular
Y
Y
Y
Y
Y
Y
Intracellular
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
MAPK
Sos
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)