Dehydration of main-chain amides in the final folding step of single-chain monellin revealed by time-resolved infrared spectroscopy

Tetsunari Kimura, Akio Maeda, Shingo Nishiguchi, Koichiro Ishimori, Isao Morishima, Takashi Konno, Yuji Goto, Satoshi Takahashi

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34 Citations (Scopus)


Kinetic IR spectroscopy was used to reveal β-sheet formation and water expulsion in the folding of single-chain monellin (SMN) composed of a five-stranded β-sheet and an α-helix. The time-resolved IR spectra between 100 μs and 10 s were analyzed based on two consecutive intermediates, I1 and I2, appearing within 100 μs and with a time constant of ≈100 ms, respectively. The initial unfolded state showed broad amide I′ corresponded to a fluctuating conformation. In contrast, I 1 possessed a feature at 1,636 cm-1 for solvated helix and weak features assignable to turns, demonstrating the rapid formation of helix and turns. I2 possessed a line for solvated helix at 1,637 cm -1 and major and minor lines for β-sheet at 1,625 and 1,680 cm-1, respectively. The splitting of the major and minor lines is smaller than that of the native state, implying an incomplete formation of the β-sheet. Furthermore, both major and minor lines demonstrated a low-frequency shift compared to those of the native state, which was interpreted to be caused by hydration of the C=O group in the β-sheet. Together with the identification of solvated helix, the core domain of I2 was interpreted as being hydrated. Finally, slow conversion of the water-penetrated core of I2 to the dehydrated core of the native state was observed. We propose that both the expulsion of water, hydrogen-bonded to main-chain amides, and the completion of the secondary structure formation contribute to the energetic barrier of the rate-limiting step in SMN folding.

Original languageEnglish
Pages (from-to)13391-13396
Number of pages6
JournalProceedings of the National Academy of Sciences of the United States of America
Issue number36
Publication statusPublished - 2008 Sep 9
Externally publishedYes


  • Protein folding dynamics
  • β-sheet

ASJC Scopus subject areas

  • General


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