A Dynamic Interaction of Coomassie Dye with the Glycine Transporters N-termini.

Coomassie Brilliant Blue interacts with proteins and even though the interactions exhibit variation due to the amino acid content, reported dye interactions with individual proteins appear to be relatively stable. Here we report an atypical dynamic interaction of glycine transporters 1 and 2 N-termini with Coomassie dye, resulting in intramolecular interference with their Bradford assay. These proteins exhibit classic protein-Coomassie G-250 complex with absorption maximum at 595 nm, which within minutes starts to decrease and parallel increase of absorbance shoulders above 300 and 700 nm is observed. Interestingly, these effects are eliminated upon fusion of glycine transporters N-termini with glutathione S-transferase protein or by the presence of glutathione S-transferase or bovine serum albumin in the same solution. Circular dichroism data revealed largely unstructured character of glycine transporters N-termini, which suggests that dynamic properties of these protein- Coomassie complexes might be a signature of high flexibility and protein disorder. The assay might potentially reveal similar domains in other proteins and help to associate them with particular functions.