Molecular dynamics of stability and structures in phytochelatin complexes with Zn, Cu, Fe, Mg, and Ca: Implications for metal detoxification
- 236 Downloads
Phytochelatins, or (γ-glutamyl-cysteine)n-glycine, are specialized peptides produced by plants and algae to mitigate toxic metal exposure, for instance in response to high levels of metals such as Cu, Cd, and Zn. Stability constants and structural characterization of metal–phytochelatin complexes are lacking. This information is required to gain mechanistic insights on the metal selectivity of phytochelatins. Here, we studied structural coordination and thermodynamic stability by performing molecular dynamics simulations of a fully hydrated phytochelatin molecule complexed with Ca2+, Mg2+, Fe2+, Zn2+, and Cu2+. Our results predict the following decreasing order for the thermodynamic stability of the phytochelatin complexes: Zn2+ ≥ Cu2+ ≥ Fe2+ > Mg2+ > Ca2+. The favorable binding energies with Zn2+ and Cu2+ over the other metal cations can be explained by shorter binding distances and greater coordination from carboxylate and keto O atoms. Conformational rearrangement of phytochelatin following metal chelation was captured by monitoring changes in the solvent-accessible volume. Accessibility of solvent molecules to the phytochelatin structure was inversely proportional to the distance between the coordinated ligands and the chelated metal. These new findings demonstrate the influence of the metal–phytochelatin structure on the metal-binding thermodynamics and the phytochelatin conformation, both of which are important to evaluate the intracellular role of phytochelatin in mediating algal response to toxic heavy metal exposure.
KeywordsPhytochelatin Heavy metal Metal toxicity Metal binding
We thank Thalia Aoki and David Flannelly for technical assistance and Beth Ahner for insightful discussions during the early stages of this work. A.L.P. acknowledges a Cornell University Graduate School Fellowship.
- Accelrys Software Inc (2013) Materials studio modeling environment, Release 7.0. Accelrys Software Inc., San DiegoGoogle Scholar
- Adams MS, Dillon CT, Vogt S, Lai B, Stauber J, Jolley DF (2016) Copper uptake, intracellular localization, and speciation in marine microalgae measured by synchrotron radiation X-ray fluorescence and absorption microspectroscopy. Environ Sci Technol 50:8827–8839. doi:10.1021/acs.est.6b00861 CrossRefGoogle Scholar
- Harris DC (2009) Exploring chemical analysis, 4th edn. W. H. Freeman and Company, BasingstokeGoogle Scholar
- Mendoza-Cózatl DG, Zhai Z, Jobe TO, Akmakjian GZ, Song W-Y, Limbo O, Russell MR, Kozlovskyy VI, Martinoia E, Vatamaniuk OK, Russell P, Schroeder JI (2010) Tonoplast–localized Abc2 transporter mediates phytochelatin accumulation in vacuoles and confers cadmium tolerance. J Biol Chem 285:40416–40426. doi:10.1074/jbc.M110.155408 CrossRefGoogle Scholar
- Pickering IJ, Prince RC, George GN, Rauser WE, Wickramasinghe WA, Watson AA, Dameron CT, Dance IG, Fairlie DP, Salt DE (1999) X-ray absorption spectroscopy of cadmium phytochelatin and model systems. Biochem Biophys Acta 1429:351–364Google Scholar