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Biophysical Journal 43: 81-89 (1983)
© 1983 the Biophysical Society

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Peptide-chain secondary structure of bacteriorhodopsin.

B K Jap, M F Maestre, S B Hayward and R M Glaeser

ABSTRACT

Ultraviolet circular dichroism spectroscopy in the interval from 190 to 240 nm and infrared spectroscopy in the region of the amide I band (1,600 cm-1 to 1,700 cm-1) has been used to estimate the alpha-helix content and the beta-sheet content of bacteriorhodopsin. Circular dichroism spectroscopy strongly suggests that the alpha-helix content is sufficient for only five helices, if each helix is composed of 20 or more residues. It also suggests that there is substantial beta-sheet conformation in bacteriorhodopsin. The presence of beta-sheet secondary structure is further suggested by the presence of a 1,639 cm-1 shoulder on the amide I band in the infrared spectrum. Although a structural model consisting of seven alpha-helical rods has been generally accepted up to this point, the spectroscopic data are more consistent with a model consisting of five alpha-helices and four strands of beta-sheet. We note that the primary amino acid sequence can be assigned to segments of alpha-helix and beta-sheet in a way that does not require burying more than two charged groups in the hydrophobic membrane interior, contrary to the situation for any seven-helix model.




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E. Goormaghtigh, J.-M. Ruysschaert, and V. Raussens
Evaluation of the Information Content in Infrared Spectra for Protein Secondary Structure Determination
Biophys. J., April 15, 2006; 90(8): 2946 - 2957.
[Abstract] [Full Text] [PDF]


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