Patellamides are cyclic pseudo-octapeptides originally extracted from the sea squirt Lissoclinum patella. They are produced by the squirt’s blue-green algae symbiont, Prochloron. Due to the high concentration of Cu^II in these blue-green algae, it was believed that patellamides form a dinuclear complex with Cu^II. The complex was widely studied in vitro, showing remarkable pH-dependent enzymatic activity as a phosphatase or carbonic anhydrase at pH 7–8, and as a glycosidase at pH 10–11. However, its role within the cellular environment had not been studied extensively.

Peter Comba, University of Heidelberg, Germany, and colleagues have synthesized model patellamides (H₄pat) and conjugated them to a fluorescent dye (Atto550). The team then used fluorescence spectroscopy and fluorescence lifetime measurements to look at the effect of Cu^II ion complexation on the photophysical properties of the H₄pat-Atto550 conjugates. The team found that Cu^II quenches the fluorescence of H₄pat-Atto550.

The researchers then showed with confocal fluorescence microscopy and flow cytometry that Prochloron cells take in H₄pat-Atto550. Incubating H₄pat-Atto550 with Cu^II lowers the fluorescence intensity inside the Prochloron cells. This indicates the presence of Cu^II-H₄pat-Atto550 complexes (example pictured) within the cells. They can be disrupted by a competitive Cu^II-chelator like cyclam.

This study is the first attempt into understanding the biological role of Cu^II-patellamides inside the Prochloron cells. It could serve as a start for further exploration of its cellular catalytic function.

• Is Cu^II Coordinated to Patellamides inside Prochloron Cells?,
  Peter Comba, Annika Eisenschmidt, Lawrence R. Gahan, Dirk-Peter Herten, Geoffrey Nette, Gerhard Schenk, Martin Seefeld,
  Chem. Eur. J. 2017.
  DOI: 10.1002/chem.201700895