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

Kimura, Tetsunari and Maeda, Akio and Nishiguchi, Shingo and Ishimori, Koichiro and Morishima, Isao and Konno, Takashi and Goto, Yuji and Takashi, Satoshi (2008) Dehydration of main-chain amides in the final folding step of single-chain monellin revealed by time-resolved infrared spectroscopy. Proceedings of the National Academy of Sciences of the United States of America, 105 (36). pp. 13391-13396. ISSN 0027-8424. PMCID PMC2533200. doi:10.1073/pnas.0801316105.

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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.

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Additional Information:© 2008 by The National Academy of Sciences of the USA. Edited by Robert L. Baldwin, Stanford University Medical Center, Stanford, CA, and approved July 10, 2008 (received for review February 10, 2008). Published online before print August 29, 2008, doi: 10.1073/pnas.0801316105. We thank Prof. Hajime Torii (Shizuoka University, Shizuoka, Japan) for numerous discussions. This study was supported by Grants-in-Aid for Scientific Research (to S.T., K.I., and I.M.) from the Ministry of Education, Culture, Sports, Science and Technology. T. Kimura was supported by a fellowship of the Japan Society for the Promotion of Science to Young Scientists. 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. The authors declare no conflict of interest. This article is a PNAS Direct Submission. This article contains supporting information online at
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Ministry of Education, Culture, Sports, Science and Technology (MEXT)UNSPECIFIED
Japan Society for the Promotion of Science (JSPS)UNSPECIFIED
Subject Keywords:protein folding dynamics; β-sheet
Issue or Number:36
PubMed Central ID:PMC2533200
Record Number:CaltechAUTHORS:KIMpnas08
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:11596
Deposited By: Archive Administrator
Deposited On:09 Sep 2008 05:48
Last Modified:08 Nov 2021 22:01

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