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2D IR spectroscopy of histidine: probing side-chain structure and dynamics via backbone amide vibrations.

Ghosh A, Tucker MJ, Gai F - J Phys Chem B (2014)

Bottom Line: It is well known that histidine is involved in many biological functions due to the structural versatility of its side chain.However, probing the conformational transitions of histidine in proteins, especially those occurring on an ultrafast time scale, is difficult.Because of the intrinsic ultrafast time resolution of 2D IR spectroscopy, we believe that the current approach, when combined with the isotope editing techniques, will be useful in revealing the structural dynamics of key histidine residues in proteins that are important for function.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemistry, University of Pennsylvania , Philadelphia, Pennsylvania 19104-6323, United States.

ABSTRACT
It is well known that histidine is involved in many biological functions due to the structural versatility of its side chain. However, probing the conformational transitions of histidine in proteins, especially those occurring on an ultrafast time scale, is difficult. Herein we show, using a histidine dipeptide as a model, that it is possible to probe the tautomer and protonation status of a histidine residue by measuring the two-dimensional infrared (2D IR) spectrum of its amide I vibrational transition. Specifically, for the histidine dipeptide studied, the amide unit of the histidine gives rise to three spectrally resolvable amide I features at approximately 1630, 1644, and 1656 cm(-1), respectively, which, based on measurements at different pH values and frequency calculations, are assigned to a τ tautomer (1630 cm(-1) component) and a π tautomer with a hydrated (1644 cm(-1) component) or dehydrated (1656 cm(-1) component) amide. Because of the intrinsic ultrafast time resolution of 2D IR spectroscopy, we believe that the current approach, when combined with the isotope editing techniques, will be useful in revealing the structural dynamics of key histidine residues in proteins that are important for function.

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Related in: MedlinePlus

2D IR spectra of the histidine amide I′ vibratorin theHis dipeptide measured at different pH values and waiting times, asindicated. The dashed line in each case indicates the peak positionat zero waiting time.
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fig2: 2D IR spectra of the histidine amide I′ vibratorin theHis dipeptide measured at different pH values and waiting times, asindicated. The dashed line in each case indicates the peak positionat zero waiting time.

Mentions: As shown (Figure 2), the 2D IR spectra ofthe His amide obtained at different pH values and two waiting times,0 and 3 ps, all show distinct transitions that are not resolved inthe corresponding FTIR spectra. Specifically, it is clear that besidesthe expected strong transition at ∼1644 cm–1, two weaker bands at ωτ of ∼1630 and1656 cm–1 exist. The presence of these bands, whichare denoted as A (1630 cm–1), B (1644 cm–1), and C (1656 cm–1), becomes even more evidentin the diagonal traces of the 2D spectra at zero waiting time (Figure 3). The diagonal traces are obtained by taking aslice of the 2D IR spectra parallel to the diagonal line that runsthrough the positive peak. As expected, these bands, either theirintensity, frequency, or both, show a measurable dependence on pH.The frequencies of all bands blue-shift by ∼2 cm–1 as the pH is lowered from 6.5 to 2, which indicates that the amideI vibrational frequency of His is sensitive to protonation/deprotonationof the imidazole ring. This result is consistent with recent workby Reppert et al.,44 which shows that theamide I vibration of a series of dipeptides depends on the protonationstates of the N- and C-termini of the peptide. As shown (Figure 3), the diagonal traces also reveal, when the pHis decreased from 10 to 6.5, that the intensity of band A shows anappreciable decrease, whereas that of band C is virtually unchangedbut shows a significant increase when the pH is further lowered to2. Taken together, these results provide further evidence that theamide I vibration of His could be used to report on the structureand protonation state of its imidazole side chain, as explained inthe following section.


2D IR spectroscopy of histidine: probing side-chain structure and dynamics via backbone amide vibrations.

Ghosh A, Tucker MJ, Gai F - J Phys Chem B (2014)

2D IR spectra of the histidine amide I′ vibratorin theHis dipeptide measured at different pH values and waiting times, asindicated. The dashed line in each case indicates the peak positionat zero waiting time.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4317052&req=5

fig2: 2D IR spectra of the histidine amide I′ vibratorin theHis dipeptide measured at different pH values and waiting times, asindicated. The dashed line in each case indicates the peak positionat zero waiting time.
Mentions: As shown (Figure 2), the 2D IR spectra ofthe His amide obtained at different pH values and two waiting times,0 and 3 ps, all show distinct transitions that are not resolved inthe corresponding FTIR spectra. Specifically, it is clear that besidesthe expected strong transition at ∼1644 cm–1, two weaker bands at ωτ of ∼1630 and1656 cm–1 exist. The presence of these bands, whichare denoted as A (1630 cm–1), B (1644 cm–1), and C (1656 cm–1), becomes even more evidentin the diagonal traces of the 2D spectra at zero waiting time (Figure 3). The diagonal traces are obtained by taking aslice of the 2D IR spectra parallel to the diagonal line that runsthrough the positive peak. As expected, these bands, either theirintensity, frequency, or both, show a measurable dependence on pH.The frequencies of all bands blue-shift by ∼2 cm–1 as the pH is lowered from 6.5 to 2, which indicates that the amideI vibrational frequency of His is sensitive to protonation/deprotonationof the imidazole ring. This result is consistent with recent workby Reppert et al.,44 which shows that theamide I vibration of a series of dipeptides depends on the protonationstates of the N- and C-termini of the peptide. As shown (Figure 3), the diagonal traces also reveal, when the pHis decreased from 10 to 6.5, that the intensity of band A shows anappreciable decrease, whereas that of band C is virtually unchangedbut shows a significant increase when the pH is further lowered to2. Taken together, these results provide further evidence that theamide I vibration of His could be used to report on the structureand protonation state of its imidazole side chain, as explained inthe following section.

Bottom Line: It is well known that histidine is involved in many biological functions due to the structural versatility of its side chain.However, probing the conformational transitions of histidine in proteins, especially those occurring on an ultrafast time scale, is difficult.Because of the intrinsic ultrafast time resolution of 2D IR spectroscopy, we believe that the current approach, when combined with the isotope editing techniques, will be useful in revealing the structural dynamics of key histidine residues in proteins that are important for function.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemistry, University of Pennsylvania , Philadelphia, Pennsylvania 19104-6323, United States.

ABSTRACT
It is well known that histidine is involved in many biological functions due to the structural versatility of its side chain. However, probing the conformational transitions of histidine in proteins, especially those occurring on an ultrafast time scale, is difficult. Herein we show, using a histidine dipeptide as a model, that it is possible to probe the tautomer and protonation status of a histidine residue by measuring the two-dimensional infrared (2D IR) spectrum of its amide I vibrational transition. Specifically, for the histidine dipeptide studied, the amide unit of the histidine gives rise to three spectrally resolvable amide I features at approximately 1630, 1644, and 1656 cm(-1), respectively, which, based on measurements at different pH values and frequency calculations, are assigned to a τ tautomer (1630 cm(-1) component) and a π tautomer with a hydrated (1644 cm(-1) component) or dehydrated (1656 cm(-1) component) amide. Because of the intrinsic ultrafast time resolution of 2D IR spectroscopy, we believe that the current approach, when combined with the isotope editing techniques, will be useful in revealing the structural dynamics of key histidine residues in proteins that are important for function.

Show MeSH
Related in: MedlinePlus