Poster Presentation Royal Australian Chemical Institute National Congress 2026

Macrocyclic binding motifs for anionic phospholipid recognition (#531)

Paris Walters 1 2 , Katrina A Jolliffe 1 2
  1. School of Chemistry, The University of Sydney, Sydney, NSW, Australia
  2. ARC Centre of Excellence for Innovations in Protein and Peptide Chemistry, Sydney, NSW, Australia

Phospholipids are the most abundant type of lipid in eukaryotic cell membranes and play major roles in various biochemical processes.1 Anionic phospholipids are of particular research interest for their implications in several diseases.2 However, due to their structural similarities, selective discrimination between different phospholipid species remains challenging.

 

Phosphatidylserine (PS) is the most abundant anionic phospholipid and a well-known molecular marker for dead and dying cells.1 Previous work has been successful targeting PS with a Zn(II) complexed dipicolylamine (Zn(II)-DPA) moiety.3 However, DPA has a relatively low binding affinity for metal cations, leading to concerns about demetallation and associated cytotoxicity. Therefore, this work presents two alternative aza-macrocyclic ligands with higher binding affinities for transition metal cations: 1,4,7-triazacyclononane (TACN) and cyclen.

 

The suitability of Zn(II) and Ni(II) complexes of TACN and cyclen for phospholipid sensing was investigated with two different fluorescence response mechanisms; intramolecular indicator displacement (IID) and solvatochromism. The selectivity and fluorescence response of these sensors was tested in liposomes containing different anionic phospholipids. These sensors displayed less intrinsic selectivity than their DPA analogues. The Zn-cyclen motif was the most promising lead, showing moderate selectivity for phosphatidic acid (PA), particularly when incorporated into a solvatochromic sensor containing PRODAN. This was then pursued in a second series of sensors containing PRODAN and two metal-complexed cyclen or TACN ligands. The addition of the second Zn-cyclen motif greatly improved the sensor’s selectivity towards PA. Further study was conducted with this sensor against a range of phosphoinositides (PIPs), towards which it showed an even greater selective response. PA and PIPs are low-abundance anionic phospholipids with emerging roles in cell signalling and metabolic processes. A selective sensor for these phospholipids would be a powerful tool for further elucidation of their roles in cells. Finally, cell imaging by confocal fluorescence microscopy revealed the cell permeability of the sensor and MTT assays confirmed its low cytotoxicity compared to comparable DPA-containing sensors. Further work will be needed to investigate the binding mode and strength between the Zn(II)-cyclen units.

  1. Harayama, T.; Riezman, H. Nat. Rev. Mol. Cell Biol. 2018, 19 (5), 281–296.
  2. Buckland, A. G.; Wilton, D. C. Biochim. Biophys. Acta BBA - Mol. Cell Biol. Lipids 2000, 1483 (2), 199–216.
  3. Zwicker, V. E.; Oliveira, B. L.; Yeo, J. H.; Fraser, S. T.; Bernardes, G. J. L.; New, E. J.; Jolliffe, K. A. Angew. Chem. Int. Ed. 2019, 58 (10), 3087–3091.