The recent development of bioorthogonal crosslinking techniques – so-called “click reactions“– offers new possibilities to study the function of compounds in cellular processes [1]. They allow for an easy conjugation of the molecules of interest with probes and, thus, make them visible by suitable imaging techniques. However, the biorthogonal reactions require functional groups not found in nature, so they need to be introduced synthetically, which can be a challenging task for natural products.
Our molecules of interest – the cyclic heptapeptides microcystins – belong to the best-studied natural products from cyanobacteria, but their physiological role within the host remains unclear [2]. Some findings suggest that they play a crucial role in the adaptation of the cyanobacteria to high light conditions [3]. However, still little is known about the underlying mechanisms, the localization of microcystins in the producing cell, or their interaction partners.
Making microcystins amenable for bioorthogonal chemistry might result in new insights into their biological function and the physiology of cyanobacteria. After labelling with a probe, the microcystins can be localized by microscopic means, or their interaction partners can be identified by proteomics-based approaches. Thus, we present a rapid and feasible technique to introduce azide- and alkyne groups into microcystins: precursor directed biosynthesis. Azide and alkyne functionalized tyrosine derivatives were added to a microcystin-YR producing Microcystis sp. strain and successfully incorporated into this congener. This allowed for the conjugation of the “clickable” microcystin with e.g. a fluorescent dye and shed a new light on their role in our subsequent physiological studies, of which first results are presented.
[1] Patterson DM, Nazarova LA, Prescher JA. ACS Chem Biol 2014; 9: 592–605
[2] Kaplan A, Harel M, Kaplan-Levy RN, Hadas O, Sukenik A, Dittmann E. Front Microbiol 2012; 3: 138
[3] Meissner S, Steinhauser D, Dittmann, E. Environ Microbiol 2015; 17(5): 1497–1509