The 20S proteasome of T. acidophilum is interacting with the CDC48
homolog ATPase (Ta0840) (Barthelme and Sauer, 2012; Forouzan et al.,
2012). This interaction was demonstrated with recombinant proteins in
pull-down and biochemical assays. However, Ta0840 was not detected
in our pull-down assays using two distinct 20S proteasome specific
scFv antibodies. This might be due to the different compositions of
lysis buffer that was used in the above mentioned experiments. This
supports the observation that to isolate loosely associated complexes
in intact shape structure-preserving buffer compositions should be determined
experimentally for each complex, regardless of the protein
separation method used to isolate them (Sun et al., 2009).
Previous proteomics studies showed that Ta0152 possesses complex
forming ability suggesting a ~500 kDa molecular weight, which size was
in good agreement with its hexadecameric homologue of Aeropyrum
pernix (Mizohata et al., 2005). Our result might indicate that the antibody
purified Ta0152 ring was prevented from ordered aggregation which
was detected in earlier studies (R. Knispel, personal communication)
therefore this complex could not be visualized by EM (data not shown).
Our scFv-antibody based two-step chromatography separation method
allowed the isolation of intact complexes from native T. acidophilum
cell extract and on the example of two well-known complexes we
demonstrated the feasibility of scFv-based purification technique for
other high molecular weight complexes. These complexes can be subjected
to biochemical and/or EM analyses however care should be taken to
carry out the experiments with several specific scFvs to avoid enzyme inhibition.
We proved the power of this method by described experiments
however to avoid unnecessary cloning steps and to increase the bait
yield creating a His-tagged nanobody displaying phage library based
on camelid immunization would be a viable option