Trimming Down a Protein Structure to Its Bare Foldons SPATIAL ORGANIZATION OF THE COOPERATIVE UNIT

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Folding of the ribosomal protein S6 is a malleable process controlled by two competing, and partly overlapping, folding nuclei. Together, these nuclei extend over most of the S6 structure, except the edge strand beta 2, which is consistently missing in the folding transition states; despite being part of the S6 four-stranded sheet, beta 2 seems not to be part of the cooperative unit of the protein. The question is then whether beta 2 can be removed from the S6 structure without compromising folding cooperativity or native state integrity. To investigate this, we constructed a truncated variant of S6 lacking beta 2, reducing the size of the protein from 96 to 76 residues (S6(Delta beta 2)). The new S6 variant expresses well in Escherichia coli and has a well dispersed heteronuclear single quantum correlation spectrum and a perfectly wild-type-like crystal structure, but with a smaller three-stranded beta-sheet. Moreover, S6(Delta beta 2) displays an archetypical v-shaped chevron plot with decreased slope of the unfolding limb, as expected from a protein with maintained folding cooperativity and reduced size. The results support the notion that foldons, as defined by the structural distribution of the folding nuclei, represent a property-based level of hierarchy in the build-up of larger protein structures and suggest that the role of beta 2 in S6 is mainly in intermolecular binding, consistent with the position of this strand in the ribosomal assembly.


  • Ellinor Haglund
  • Jens Danielsson
  • Saraboji Kadhirvel
  • Magnus O. Lindberg
  • Derek Logan
  • Mikael Oliveberg
Research areas and keywords

Subject classification (UKÄ) – MANDATORY

  • Biological Sciences
Original languageEnglish
Pages (from-to)2731-2738
JournalJournal of Biological Chemistry
Issue number4
Publication statusPublished - 2012
Publication categoryResearch