So you’re finally ready to start working with your precious protein sample when BAM!- massive disappointment- it has lost its functionality. Worse, you found out about this tragedy too late, let’s say at the end of an excruciating protein purification procedure or after detailed biophysical and structural characterization experiments had already been done.
This scenario leaves us questioning: How could I prevent this from happening again?– and if it happens anyway- How could I become aware of this problem soon enough?– that is, before going further with experimental analyses that require investing time and money.
The answer to the first question will often point towards improving sample handling and experimental technique issues in general. The answer to the second one points toward performing quality analyses on protein samples on a regular basis, meaning throughout the experimental life of a protein sample.
Quality analyses include performing functional assays that rely mainly on protein’s catalytic and binding properties. Really? On binding properties?
Proteins that lose their binding ability lose their functionality
The functions of all proteins depend on their ability to bind to other molecules or ligands. For example, antibodies bind to bacteria or viruses to tag them for destruction, tubulin molecules bind to each other to form microtubules that allow movements in eukaryotic cells and lysozyme kill bacteria by binding to their cell wall and breaking it down.
Thus, interactions detected on a system can serve as an initial test of functionality. The trick though is to find a quick yes/no binding check method that allows the analysis of a sample as many times as needed, without consuming too much of it.