Defining the Structure of a Protein-Spherical Nucleic Acid Conjugate and Its Counterionic Cloud

Kurinji Krishnamoorthy, Kyle Hoffmann, Sumit Kewalramani, Jeffrey D. Brodin, Liane M. Moreau, Chad A. Mirkin, Monica Olvera De La Cruz, Michael J. Bedzyk*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

25 Scopus citations


Protein-spherical nucleic acid conjugates (Pro-SNAs) are an emerging class of bioconjugates that have properties defined by their protein cores and dense shell of oligonucleotides. They have been used as building blocks in DNA-driven crystal engineering strategies and show promise as agents that can cross cell membranes and affect both protein and DNA-mediated processes inside cells. However, ionic environments surrounding proteins can influence their activity and conformational stability, and functionalizing proteins with DNA substantively changes the surrounding ionic environment in a nonuniform manner. Techniques typically used to determine protein structure fail to capture such irregular ionic distributions. Here, we determine the counterion radial distribution profile surrounding Pro-SNAs dispersed in RbCl with 1 nm resolution through in situ anomalous small-angle X-ray scattering (ASAXS) and classical density functional theory (DFT). SAXS analysis also reveals the radial extension of the DNA and the linker used to covalently attach the DNA to the protein surface. At the experimental salt concentration of 50 mM RbCl, Rb+ cations compensate ∼90% of the negative charge due to the DNA and linker. Above 75 mM, DFT calculations predict overcompensation of the DNA charge by Rb+. This study suggests a method for exploring Pro-SNA structure and function in different environments through predictions of ionic cloud densities as a function of salt concentration, DNA grafting density, and length. Overall, our study demonstrates that solution X-ray scattering combined with DFT can discern counterionic distribution and submolecular features of highly charged, complex nanoparticle constructs such as Pro-SNAs and related nucleic acid conjugate materials.

Original languageEnglish (US)
Pages (from-to)378-386
Number of pages9
JournalACS Central Science
Issue number3
StatePublished - Mar 28 2018

ASJC Scopus subject areas

  • Chemical Engineering(all)
  • Chemistry(all)


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