Mode of action of redox-active, sulfur-containing secondary metabolites from plants and their applicationCopyright: © Martin Gruhlke
Phytoanticipins are defense molecules of plants which are present prior to an attach or injury of plant tissue and can be rapidly released or produced without demand of energy after attack by a pathogen. We are mainly interested, how allicin, a defense molecule from garlic Allium sativum, acts as a toxin in bacteria, fungi, plants and animal cells on a physiological level. Furthermore, our aim is to find out how cells are able to resist to allicin. Allicin is the first and quantitatively most important defense compound upon damage of garlic tissue and is responsible for garlic's typical smell and taste. It reacts with free thiol groups, which are present in many proteins (due to the amino acid cysteine) and the important redox buffer glutathione. Allicin oxidized thiols and we were able to show that a shift of the oxidation state is in important aspect to understand allicin's toxicity. Since garlic is used as a spice and also in medicine since ancient times, there is a interest to understand the physiological basis of allicins activity in the cell. We were able to contribute some new findings to answer the question. The oxidative activitiy of allicin, for instance, leads to a programmed cell death (apoptosis). Using the model system baker's yeast we were able to show allicin's apoptosis-inducing activity for the first time in fungi. Beyond this, also redox-sensitive transcription factors are activitated in yeast and also human cells by allicin.
In different organisms we were able to find out, which proteins are modified by allicin using an LC-MS approach. A big aim of our group is to figure out which of the oxidized proteins are relevant for the physiological consequences. Using a highly allicin-resistant bacterium, which we isolated from garlic cloves, we found evolutionary aspects leading to resistance. Beyond this redox-aspects, allicin is also membrane active and this contributes also to the toxicity of the molecule.