A hierarchic approach to the design of hexameric helical barrels

Giovanna Ghirlanda, James D. Lear, Nancy L. Ogihara, David Eisenberg, William F. DeGrado

Research output: Contribution to journalArticlepeer-review

33 Scopus citations


The design of large macromolecular assemblies is an endeavor with implications for protein engineering as well as nanotechnology. A hierarchic approach was used to design an antiparallel hexameric, tubular assembly of helices. In previous studies, a domain-swapped, dimeric three-helix bundle was designed from first principles. In the crystal lattice, three dimers associate around a 3-fold rotational axis to form a hexameric assembly. Although this hexameric assembly was not observed in solution, it was possible to stabilize its formation by changing three polar residues per monomer to hydrophobic (two Phe and one Trp) residues. Molecular models based on the crystallographic coordinates of DSD (PDB accession code 1G6U) show that these side-chains pack in the central cavity (the "supercore") of the hexameric bundle. Analytical ultracentrifugation, fluorescence spectroscopy, CD spectroscopy, and guanidine-HCl denaturation were used to determine the assembly of the hexamer. To probe the requirements for stabilizing the hexamer, we systematically varied the polarity and steric bulk of one of the Phe residues in the supercore of the hexamer. Depending on the nature of this side-chain, it is possible to modulate the stability of the hexamer in a predictable manner. This family of hexameric proteins may provide a useful framework for the construction of proteins that change their oligomeric states in response to binding of small molecules.

Original languageEnglish (US)
Pages (from-to)243-253
Number of pages11
JournalJournal of molecular biology
Issue number1
StatePublished - 2002
Externally publishedYes


  • Coiled-coils
  • Domain-swapped dimer
  • Helical barrels
  • Protein design
  • Supramolecular assembly

ASJC Scopus subject areas

  • Biophysics
  • Structural Biology
  • Molecular Biology


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