April 5 : A collaborative study has for the first time determined how plant hormone, auxin, interacts with its receptor TIR1.

The study, conducted by scientist from the University of Washington School of Medicine, Indiana University Bloomington and the University of Cambridge, may have important implications for the treatment of cancers that afflict human beings, as TIR1 is similar to human enzymes that are known to be involved in cancer.

“Learning that auxin regulates TIR1 is a huge advance for plant biology that will probably have important implications for agriculture in the future,” Nature magazine quoted IU Bloomington plant biologist, Mark Estelle, as saying.

“It’s a bonus for us that TIR1 is related to proteins in other organisms, including humans. Some of TIR1’s human relatives play a role in different human cancers, and it is possible that our work on plants will eventually lead to new cancer drugs,” he added.

During the study, the scientists extracted and purified TIR1 from the common plant model Arabidopsis. By x-raying crystals of the protein, they determined the enzyme’s three-dimensional structure, a first for plant hormone receptors.

Thereafter, the crystals were soaked in a solution containing auxin, and the x-ray treatment was repeated to determine where the auxin had bound. Finally, the scientists added a peptide that TIR1 is known to bind and modify.

The scientists noted that auxin is a sort of “molecular glue” that improves the ability of TIR1, also known as ubiquitin ligases, to bind its peptide target, and that in the absence of auxin, TIR1 does not bind its target as tightly.

“A number of human disorders including Parkinson’s disease, and colon and breast cancers, are caused by defective interactions between ubiquitin ligases and their substrate polypeptides. What the plant hormone tells us is that it might be possible to rescue these interactions using small molecules,” said University of Washington School of Medicine pharmacologist Ning Zheng, who led the research. (ANI)