Is Cu^II coordinated to patellamides inside prochloron cells?

Dinuclear Cu^II–patellamide complexes (patellamides are naturally occurring cyclic pseudo‐octapeptides) are known to be efficient catalysts for hydrolysis reactions of biological importance, for example, those of phosphatase, carbonic anhydrase, and glycosidase. However, the biological role of patellamides is still unknown. Patellamides were originally extracted from the sea squirt Lissoclinum patella, but are now known to be ribosomally expressed by the blue‐green algae Prochloron that live in symbiosis with L. patella. In a further step to unravel the metabolic significance of the patellamide complexes, the question as to whether these are also formed inside Prochloron cells is addressed. In this study, a biocompatible patellamide–fluorescent dye conjugate has been introduced into living Prochloron cells and, by means of flow cytometry and confocal microscopy, it is shown that Cu^II ions are coordinated to patellamides in vivo.