APR January/February 2022 - 37

long run, as secondary purification steps can be avoided. This is of particular interest in
high-throughput screening, or where proteins are expressed at low levels, for example
while expression conditions are being optimized.
There are several formats for chromatography media to capture recombinant proteins.
The most common are cross-linked agarose conjugates of antibodies to specific protein
tags, which can be used in batch column or multiwell plate format. Of late, magnetic
agarose beads ( " magnetic beads " ), which contain a magnetic core surrounded by
cross-linked agarose, are increasingly being used to purify recombinant proteins because
of their time-saving qualities and speed when used with a suitable magnet to capture
the beads.
If the biotherapeutic is an antibody there is a more elegant purification strategy available
than tagging. Here, the long-standing procedures center around using Protein A, Protein
G, and Protein L as affinity ligands to capture the therapeutic antibodies. These proteins
have an inherent native affinity for immunoglobulins, so there is no need to use specific
antibodies for capture.
Removing the tag
In some instances, the protein tag must be removed after purification of the target
protein. Various proteases exist to remove such tags. The enzymes are specific to given
sequences where the tag is attached, allowing them to selectively cleave the tag.
While there are scientists that come up with novel tags for niche uses, most are generally
reluctant to give up the well-established tags they have been using. This is because a
new protein tag means having to use new cloning and expression vectors to express
the protein with the tag, along with a new suitable chromatography resin to capture the
protein with its novel tag. However, if a combination of tag and chromatography resin is
well-tried and promises greater purity, it should be worth considering.
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Germany and/or its affi liates.
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APR January/February 2022

Table of Contents for the Digital Edition of APR January/February 2022

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