Bradavidin is a homotetrameric biotin-binding protein from Bradyrhizobium japonicum, a nitrogen fixing and root nodule-forming symbiotic bacterium of the soybean. Wild-type (wt) bradavidin has 138 amino acid residues, whereas the C-terminally truncated core-bradavidin has only 118 residues. We have solved the X-ray structure of wt bradavidin and found that the C-terminal amino acids of each subunit were uniquely bound to the biotin-binding pocket of an adjacent subunit. The biotin-binding pocket occupying peptide (SEKLSNTK) was named "Brad-tag" and it serves as an intrinsic stabilizing ligand in wt bradavidin. The binding of Brad-tag to core-bradavidin was analysed by isothermal titration calorimetry and a binding affinity of ~25 ?M was measured. In order to study the potential of Brad-tag, a green fluorescent protein tagged with Brad-tag was prepared and successfully concentrated from a bacterial cell lysate using core-bradavidin-functionalized Sepharose resin. ? 2012 Leppiniemi et al.
Leppiniemi, J., Grönroos, T., Määttä, J. A. E., Johnson, M. S., Kulomaa, M. S., Hytönen, V. P., & Airenne, T. T. (2012). Structure of Bradavidin - C-terminal residues act as intrinsic ligands. PLoS ONE, 7(5). https://doi.org/10.1371/journal.pone.0035962