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The Eph Receptor Family,
by Elena Pasquale from the Burnham Institute.
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The Eph receptors are divided into two groups,
the EphA receptors and the EphB receptors.
These receptors bind ligands which are called
Ephrins and which are also membrane-associated.
The EphA receptors preferentially bind
the ephrin-A ligands which are GPI-linked molecules.
The EphB receptors preferentially bind
the ephrin-B ligands which are transmembrane molecules.
With regard to the domain structure,
the Eph receptors contain tyrosine kinase domain in their cytoplasmic region.
This domain is linked to the membrane by juxtamembrane region and is followed on
the carboxy-terminal side by SAM domain and
the PDZ domain-binding site at the extreme carboxy-terminus.
On the extracellular side,
there are two fibronectin type three repeats,
a cysteine-rich region and the ephrin-binding domain at the extreme amino-terminus.
The extracellular domain on the ephrins is almost
entirely occupied by the Eph receptor-binding domain.
The ephrin-B ligands also have a short carboxy-terminal tail
with a PDZ domain-binding site at the extreme carboxy-terminus.
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There are 10 EphA receptors,
six EphB receptors, six ephrin-A ligands and three ephrin-B ligands.
However, the EphA9 receptor,
the EphB5 receptor and the ephrin-A6 ligand have
been identified in the chicken and they are not present in the mouse and human genomes.
Also, residues that are thought to be important for kinase activity are not
conserved in the EphA10 receptor and EphB6 receptor.
In fact, EphB6 is
an inactive receptor and EphA10 has not yet been tested for kinase activity.
This slide shows phylogenetic trees for the Eph receptors and the ephrins.
