Chemokines can be grouped
into four different family.
They are essentially
But that’s not the only thing they do, they don’t just act as
chemotactic factors, they have multiple other effects as well.
The four families are defined based upon the
arrangement of cysteine amino acids in their structure.
So the C family chemokines just have a
single cysteine that forms a disulphide bond.
And there are quite a few
members of this family.
One example is a chemokine called lymphotactin
or XCL1, to give it its alternative name.
The CC family of chemokines have two cysteine
residues that are next to each other.
So two adjacent cysteine residues.
And an example of a CC family
chemokine is RANTES or CCL5.
CXC family chemokines have two cysteines
that are separated by a single amino acid.
It really doesn’t matter
which amino acid that is.
It can be any amino acid, that’s what
the X represents here, that they have a
cysteine, then another amino acid, and
then a cysteine; CXC family chemokines.
An example of a CXC family
chemokine is interleukin-8.
Interluekin-8 is a member of the interleukin
cytokines that has chemotactic activity.
It can also be designated as CXCL8.
And then finally, the fourth member of
the chemokine family is the CX3C family.
And here, you probably guess by now,
they have a cysteine, then three
amino acids, can be any three amino
acids; and then another cysteine.
So two cysteines separated
by three amino acids.
An example of a CX3C family
chemokine is fractalkine or CX3CL1.
Chemokines form a
So they’ll be produced in
response to a stimulus.
And the place where they’re being produced,
they’ll be at their highest concentration.
And then further away from that location,
the concentration will decrease.
So the lymphocytes move on
the concentration gradient.
In order to do that, they need to
detect the presence of a chemokine.
So they have chemokine
receptors on their surface.
And the chemokine receptors are typically members of a
7-transmembrane receptor family that are linked to G-proteins.
So they have a rather convoluted transmembrane sequence
that passes through the cell surface membrane seven times.
And just underlying the cell membrane is a G-protein
consisting of three units - alpha (α), beta (β) and gamma (γ).
And when the chemokine binds to its
receptor, a signaling event is initiated
leading to cell activation and migration
of the cells up the chemokine gradient.