A wide variety of
ligand coated beads,
from small molecules
to large proteins
The protein mixture is applied to the
column, with all but the protein with a
specific interaction for the ligand being
washed away in the ‘flow through’.
Specifically bound proteins
are then eluted using a
competing ligand to dislodge
the affinity interaction.
Ion-exchange chromatography
Increasing salt concentrations are used
to compete for the ionic interactions
between the proteins and the beads. The
proteins are then eluted from the column
e.g. Cation exchange
CM carboxy-methyl
Anion exchange
DEAE diethylaminoethyl
SDS-PAGE
Acrylamide gel concentration has a sieving effect,
and protein migration through the gel in the presence
of SDS is proportional to molecular mass.
2D gels
1st dimension isoelectric
focussing separates by charge
2nd dimension SDS-PAGE
separates based on size
2-D gels are like a
‘fingerprint’ of the
original protein sample
Used in proteomics
Western blotting
The gel is electrophoretically
transferred to a membrane.
Membrane incubated with specific antibody
against component of mixture.
The ‘primary’ antibody is detected
with a ‘secondary’ antibody with an
enzyme linked to it.
Western blot ‘developed’ using chemicals that the
linked enzyme converts to colour or light.
Reaction revealed directly as coloured spots or using a camera.
Once the position of a protein spot of interest is
identified, it can be cut out of the gel and subjected
to further analysis by mass spectrometry.
This can be used to determine the
identity of unknown spots, or to identify
post-translational modification of
proteins
Mass spectrometry
DNA binding proteins recognise specific DNA sequences
DNA Footprinting
Mapping of specific protein-DNA binding
sites to identify, for example regulatory
regions, such as promoters.
Also to test the regulation of
known DNA-binding proteins by
other factors, such as
phosphorylation or the binding of an
enhancer protein etc.
Gel mobility shift assays -
identifying DNA binding proteins