Interrupted hydrogen/deuterium exchange reveals the stable core of the remarkably helical molten globule of a-ß parallel protein flavodoxin

S.M. Nabuurs, C.P.M. van Mierlo

Research output: Contribution to journalArticleAcademicpeer-review

19 Citations (Scopus)

Abstract

Kinetic intermediates that appear early during protein folding often resemble the relatively stable molten globule intermediates formed by several proteins under mildly denaturing conditions. Molten globules have a substantial amount of secondary structure but lack virtually all tertiary side-chain packing characteristics of natively folded proteins. Due to exposed hydrophobic groups, molten globules are prone to aggregation, which can have detrimental effects on organisms. The molten globule that is observed during folding of a-ß parallel flavodoxin from Azotobacter vinelandii is a remarkably non-native species. This folding intermediate is helical and contains no ß-sheet and is kinetically off-pathway to the native state. It can be trapped under native-like conditions by substituting residue Phe44 for Tyr44. To characterize this species at the residue level, in this study, use is made of interrupted hydrogen/deuterium exchange detected by NMR spectroscopy. In the molten globule of flavodoxin, the helical region comprising residues Leu110-Val125 is shown to be better protected against exchange than the other ordered parts of the folding intermediate. This helical region is better buried than the other helices, causing its context-dependent stabilization against unfolding. Residues Leu110–Val125 thus form the stable core of the helical molten globule of a-ß parallel flavodoxin, which is almost entirely structured. Non-native docking of helices in the molten globule of flavodoxin prevents formation of the parallel ß-sheet of native flavodoxin. Hence, to produce native a-ß parallel protein molecules, the off-pathway species needs to unfold
Original languageEnglish
Pages (from-to)4165-4172
JournalJournal of Biological Chemistry
Volume285
Issue number6
DOIs
Publication statusPublished - 2010

Keywords

  • azotobacter-vinelandii apoflavodoxin
  • folding intermediate
  • hydrogen-exchange
  • unfolded molecules
  • energy landscape
  • on-pathway
  • aggregation
  • equilibrium
  • lactalbumin
  • apomyoglobin

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