Prebiotic Alternatives to Proteins: Structure and Function of Hyperbranched Polyesters

  • Irena Mamajanov
  • Michael P. Callahan
  • Jason P. Dworkin
  • George D. Cody


Proteins are responsible multiple biological functions, such as ligand binding, catalysis, and ion channeling. This functionality is enabled by proteins’ three-dimensional structures that require long polypeptides. Since plausibly prebiotic synthesis of functional polypeptides has proven challenging in the laboratory, we propose that these functions may have been initially performed by alternative macromolecular constructs, namely hyperbranched polymers (HBPs), during early stages of chemical evolution. HBPs can be straightforwardly synthesized in one-pot processes, possess globular structures determined by their architecture as opposed to folding in proteins, and have documented ligand binding and catalytic properties. Our initial study focuses on glycerol-citric acid HBPs synthesized via moderate heating in the dry state. The polymerization products consisted of a mixture of isomeric structures of varying molar mass as evidenced by NMR, mass spectrometry and size-exclusion chromatography. Addition of divalent cations during polymerization resulted in increased incorporation of citric acid into the HBPs and the possible formation of cation-oligomer complexes. The chelating properties of citric acid govern the makeup of the resulting polymer, turning the polymerization system into a rudimentary smart material.


Hyperbranched polymer Polyester Smart material Protein Size exclusion chromatography 



We thank Dr. Leslie Gelbaum for his help in the design of NMR experiments and Prof. Nicholas Hud for helpful discussions. This work is supported by Simons Foundation Collaboration on the Origin of Life Fellowship SCOL 292864 (I.M.) and Investigator Award SCOL 302497 (M.P.C., J.P.D.), as well as the NASA Astrobiology Institute award to the Carnegie Institution for Science (I.M., G.D.C.) and The Goddard Center for Astrobiology (M.P.C., J.P.D.).

Supplementary material

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Figure S1

1H NMR spectra of a) glycerol triacetate; b) glycerol diacetate, mixture of isomers, contains mono- and triacetate c) glycerol monoacetate, mixture of isomers, contains di- and triacetate. The samples were buffered by citric acid. (GIF 42 kb)

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Figure S2

ACD chemical shift prediction for a characteristic glycerol-citric acid polymer fragment. Predicted a) 1H and b) 13C chemical shifts. (GIF 51 kb)

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Figure S3

SEC analysis (UV trace) of glycerol-citric acid oligomers synthesized in neat and in the presence of 0.125, 0.25 and 0.5 eqivalents of MgCl2. Similar behavior is observed in the CaCl2, CoCl2, CuCl2, NiCl2 and ZnCl2 systems. (GIF 71 kb)

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High Resolution Image (TIFF 14409 kb)


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Copyright information

© Springer Science+Business Media Dordrecht 2015

Authors and Affiliations

  • Irena Mamajanov
    • 1
  • Michael P. Callahan
    • 2
  • Jason P. Dworkin
    • 2
  • George D. Cody
    • 1
  1. 1.Geophysical LaboratoryCarnegie Institution for ScienceWashingtonUSA
  2. 2.Solar System Exploration Division and The Goddard Center for AstrobiologyNational Aeronautics and Space Administration Goddard Space Flight CenterGreenbeltUSA

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