The effect of many drugs is based on influencing the metabolism of cells by specifically inhibiting the activity of certain proteins. The active substance molecule must bind to the respective target protein, whereby the active substance usually settles in the often pocket-like deepened functional areas of proteins. For some drugs, binding to the target protein also alters the structure of the protein surface. Such a so-called conformational change opens up new surface areas and binding pockets to which an active ingredient can be further adapted. This often leads to better selectivity of active ingredients and thus to fewer side effects.
"The influence of an active substance on the structure of a target protein has so far been investigated using very time-consuming and material-intensive methods that provide very detailed spatial information but only produce results after weeks or months," explains Dr. Jörn Güldenhaupt from the Ruhr University Bochum. The method developed by the Bochum researchers provides information on structural changes within minutes and can even narrow down the types of structural change.
The sensor is based on a crystal that transmits infrared light. The target protein is bound on its surface. The infrared spectra are recorded through the crystal, while solutions with or without active ingredient are rinsed over the surface at the same time. The sensor detects changes in the structure-sensitive spectral range of the protein, the so-called amide region, which is characteristic of the structure of a protein. If there are changes here, it is clear that the active ingredient has changed the protein form.
The reliability of the method was demonstrated by the team in cooperation with Merck by investigating the influence of two different groups of active substances on the heat shock protein HSP90. It is a folding aid that helps the newly produced proteins of the cell to form the correct three-dimensional structure. Tumor cells need it particularly urgently due to their very active metabolism. HSP90 inhibitors are an approach to drugs that inhibit tumor growth.
The speed at which an active substance molecule is released from the target protein corresponds to the time it takes for the drug to take effect in the body. Active ingredients with a long complex lifetime remain bound to the target protein for a long time and therefore often have a long effect. For example, tablets containing such active ingredients only have to be taken once a day and often have fewer side effects.
"Because our sensor works as a flow system, after binding we can rinse the active substances from the target protein again and thus also measure the temporal course of effectiveness," sums up researcher Dr. Klaus Gerwert from the Ruhr University.