Salk scientists have developed a versatile platform that allows to detect low-affinity and transient protein-protein interactions in living cells in real time. This approach, published in Cell Reports, would dramatically accelerate the identification of many potential new drug targets and provide an immediate platform to screen for badly needed new drug candidates that disrupt abnormal protein interactions.

As known in the biomedical circle, the number of protein interactions that are currently targeted by drugs is incredibly small compared to the total number of protein interactions that could be targeted for therapeutic benefit. It will be of massive breakthrough that scientists can crack the nut of screening for drugs that disrupt cancer-relevant protein interactions, with implications for many diseases including cancer.

Scientists attempt to visualize these brief and transient interactions between proteins via using a molecule called luciferase, an enzyme that generates bioluminescence. They adapted an old method in which luciferase is split in half, and then attached each half to two proteins of interest. During the proteins associate, luciferase’s two halves are brought together and emit light.

ReBiL as a enhanced tool

The secret to the new method comes in the many tweaks and improvements, which is symbolized by the acronym applying to the method — ReBiL — which indicates “recombinase enhanced bi-molecular luciferase complementation.”

To test the approach, investigators applied it to the interaction between two proteins, Ube2t and FANCL, that had never been seen in living mammalian cells. These proteins involved in the cell’s ability to detect and repair DNA damage, a function that is often disrupted in diseases. The ability of ReBiL to reveal the stealthy FANCL-Ube2t reaction suggested the method could be a powerful technique for observing other similarly challenging interactions.

The Salk scientists then used ReBiL to study a promising target for cancer, the interaction between the proteins p53 and Mdm2. The function of p53 is affected in almost all cancers and, in many cancers, too much Mdm2 prevents p53 from functioning properly. Hence, a major goal of cancer scientists has been to develop drugs that prevent Mdm2 from binding to p53, and to thereby activate p53 to kill the tumor cell.

Additionally, the scientists used ReBiL to confirm that some drugs work as expected to prevent Mdm2 from binding to p53. On the other hand, when they applied this new method to a new class of promising drugs called stapled peptides, they found that the drugs had difficulty entering cells and had the unexpected and unintended ability to kill cells by punching holes in their protective membrane. ReBiL provides a fast and simple way to try to improve stapled peptides to enable them to get into the cell, bind to their targets and kill cells by the specific route they were designed to use.

Reference:

A Versatile Platform to Analyze Low-Affinity and Transient Protein-Protein Interactions in Living Cells in Real Time. Cell Reports, 2014