Astins are cyclic peptides isolated from the roots of the plant Aster tataricus. Root extracts show antibacterial activity; besides, astin derivatives possess also a high anti-tumor potential. Only very low amounts of astins can be isolated from plants and they are difficult to synthesize chemically without negative impacts on the environment. The MESIAB project with research groups from Finland, France, Germany and The Netherlands aims at enhancing the production of astins using molecular genetic tools. Thus, the genes required for astin biosynthesis shall be detected and cloned. From the structure of astins it can be concluded that they are produced via nonribosomal peptide synthesis (NRPS) including proline dehydrogenation and chlorination steps.
Besides the production of astins by Aster tataricus, it was discovered that Penicillium islandicum produces cyclochlorotines, which are highly similar in structure to astins. Therefore, the genome of P. islandicum was sequenced and genes detected which are involved in the synthesis of cyclochlorotines. As working with fungi P. islandicum should be faster and easier than working with the plant A. tataricus, these fungal genes are being investigated for the production of astins.
The project in Wageningen concentrates on the identification of proline dehydrogenases (PRODHs). Astins/cycloclorotinees contain a dichlorinated proline residue, which synthesis requires the action of flavin-dependent dehydrogenases and halogenases. Three potential PRODH genes from P. islandicum have been identified. After cloning of the genes, the enzymes will be isolated and characterized and their role in the synthesis of cyclochlorotines and the potential synthesis of astins will be investigated. In addition, the biochemical properties of PRODHs from the hyperthermophilic archea Thermus thermophilus (White, et al.,2007) will be investigated for their possible application in astin synthesis.