Detection of threonine structural changes upon formation of the M-intermediate of bacteriorhodopsin: Evidence for assignment to Thr-89

Xiaomei Liu, Min Joo Lee, Matthew A Coleman, Parshuram Rath, Anders Nilsson, Wolfgang B. Fischer, Marina Bizounok, Judith Herzfeld, Willem F. Jan Karstens, Jan Raap, Johan Lugtenburg, Kenneth J. Rothschild

Research output: Contribution to journalArticle

7 Scopus citations

Abstract

The behavior of threonine residues in the bacteriorhodopsin (bR) photocycle has been investigated by Fourier transform infrared difference spectroscopy. l-Threonine labeled at the hydroxyl group with 18O (l-[3-18O]threonine) was incorporated into bR and the bR→M FTIR difference spectra measured. Bands are assigned to threonine vibrational modes on the basis of 18O induced isotope frequency shifts and normal mode calculations. In the 3500 cm-1 region, a negative band is assigned to the OH stretch of threonine. In the 1125 cm-1 region, a negative band is assigned to a mixed CH3 rock/CO stretch mode. The frequency of both these bands indicates the presence of at least one hydrogen bonded threonine hydroxyl group in light adapted bR which undergoes a change in structure by formation of the M intermediate. Spectral changes induced by the substitution Thr-89→Asn but not Thr-46→Asn or Asp-96→Asn are consistent with the assignment of these bands to Thr-89. These results along with another related study on the mutant Thr-89→Asn indicate that the active site of bR includes Thr-89 and that its interaction with the retinylidene Schiff base and Asp-85 may play an important role in regulating the color of bacteriorhodopsin and the transfer of a proton to the Schiff base. Copyright (C) 1998 Elsevier Science B.V.

Original languageEnglish (US)
Pages (from-to)363-372
Number of pages10
JournalBiochimica et Biophysica Acta - Bioenergetics
Volume1365
Issue number3
DOIs
StatePublished - Jul 20 1998
Externally publishedYes

Keywords

  • Bacteriorhodopsin
  • Fourier transform infrared
  • Isotope labeling
  • Proton transport
  • Site directed mutagenesis
  • Threonine

ASJC Scopus subject areas

  • Biophysics

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  • Cite this

    Liu, X., Lee, M. J., Coleman, M. A., Rath, P., Nilsson, A., Fischer, W. B., Bizounok, M., Herzfeld, J., Jan Karstens, W. F., Raap, J., Lugtenburg, J., & Rothschild, K. J. (1998). Detection of threonine structural changes upon formation of the M-intermediate of bacteriorhodopsin: Evidence for assignment to Thr-89. Biochimica et Biophysica Acta - Bioenergetics, 1365(3), 363-372. https://doi.org/10.1016/S0005-2728(98)00088-7