PNAS Profile of NAS member Angelika Amon, winner of the 2019 Vilcek Prize in Biomedical Science
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Edited by Robert L. Baldwin, Stanford University Medical Center, Stanford, CA, and approved July 10, 2008 (received for review February 10, 2008)
Abstract
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, I1 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.
Footnotes
- **To whom correspondence should be addressed. E-mail: st{at}protein.osaka-u.ac.jp
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Author contributions: T. Kimura, K.I., I.M., Y.G., and S.T. designed research; T. Kimura, A.M., and K.I. performed research; S.N. and T. Konno contributed new reagents/analytic tools; T. Kimura and S.T. analyzed data; and T. Kimura and S.T. wrote the paper.
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↵‡Present address: Beckman Institute, California Institute of Technology, Pasadena, CA 91125.
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↵§Present address: Division of Chemistry, Graduate School of Science, Hokkaido University, Sapporo 060-0810, Japan.
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The authors declare no conflict of interest.
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This article is a PNAS Direct Submission.
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This article contains supporting information online at www.pnas.org/cgi/content/full/0801316105/DCSupplemental.
- © 2008 by The National Academy of Sciences of the USA
Dehydration of main-chain amides in the final folding step of single-chain monellin revealed by time-resolved infrared spectroscopy
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