Unfolded BPTI variants with a single disulfide bond have diminished non-native structure distant from the crosslink

Elisar Barbar, George Barany, Clare Woodward

Research output: Contribution to journalArticlepeer-review

20 Scopus citations


Background: NMR studies of denatured states, both fully unfolded and partially folded, give insight into the conformations and interactions favored in initial stages of folding, and in early intermediates formed during folding. We have characterized non-random structures favored in unfolded, reduced BPTI [1], and in partially folded BPTI [2]. Here, we report NMR-detected structure of two analogs of unfolded BPTI with one native 14-38 disulfide bond. Results: Analogs Y21A[14-38]Abu and Y23A[14-38]Abu, obtained by chemical synthesis of [14-38]Abu with Y21 or Y23 replaced by alanine, are models for unfolded BPTI with 14-38 the only disulfide. Compared to unfolded BPTI with all three disulfides broken, the unfolded 14-38 BPTI analogs have numerous differences, including loss of non-native, turn-like conformations for β2 residues, diminished non-native aromatic-aliphatic NOEs, and increased intermediate chemical exchange of residues that have native-like conformations in partially folded BPTI. Although the Y21A and Y23A analogs have similar CD and NMR properties, specific differences in NOE patterns and in exchange broadening are observed. Conclusions: Changes in unfolded BPTI associated with formation of the 14-38 disulfide bond are consistent with less non-native structure, and more native-like structure, in residues composing the stable core of antiparallel β-sheet in pactially folded BPTI. Specific differences between Y21A[14-38]Abu and Y23A[14-38]Abu indicate that replacement of Y23 results in less ordered structure than replacement of Y21.

Original languageEnglish (US)
Pages (from-to)65-76
Number of pages12
JournalFolding and Design
Issue number1
StatePublished - 1996

Bibliographical note

Funding Information:
This work was supported by NIH grants GM 26242 (C.W.), and GM 51628 (G.B. and C.W.)


  • BPTI
  • Denatured states
  • Disulfide bonds
  • NMR
  • Protein folding


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