Assessing molecular interactions with biophysical methods using the validation cross

There are numerous methods for studying molecular interactions. However, each method gives rise to false negative- or false positive binding results, stemming from artifacts of the scientific equipment or from shortcomings of the experimental format. To validate an initial positive binding result, additional methods need to be applied to cover the short-comings of the primary experiment. The aim of such a validation procedure is to exclude as many artifacts as possible to confirm that there is a true molecular interaction that meets the standards for publishing or is worth investing considerable resources for follow-up activities in a drug discovery project. To simplify this validation process, a graphical scheme - the validation cross - can be used. This simple graphic is a powerful tool for identifying blind spots of a binding hypothesis, for selecting the most informative combination of methods to reveal artifacts and, in general, for understanding more thoroughly the nature of a validation process. The concept of the validation cross was originally introduced for the validation of protein-ligand interactions by NMR in drug discovery. Here, an attempt is made to expand the concept to further biophysical methods and to generalize it for binary molecular interactions.