Helical and reverse turn changes in the BR->N transition of bacteriorhodopsin.
Fourier transform infrared deconvoluted spectra of bacteriorhodopsin and the N intermediate were compared with the N/BR infrared difference spectrum. In the amide I, clear changes in the bands at 1666 cm-1, assigned to alpha II helices, 1659 cm-1, assigned to alpha I and alpha II helices, and 1652 cm-1, assigned to both alpha I helices and unordered structures, were found. These changes could arise from conversion of some alpha II and alpha I helices. Variations in the bands at 1692 and 1683 cm-1, corresponding to reverse turns, were also detected. The side chains of Tyr (band at 1517 cm-1) and Phe (band at 1498 cm-1) were found to change in going from BR to N. In the carboxylate region, no band was detected at 1737 cm-1 in the deconvoluted spectra that could correspond to the peak observed in the difference spectrum. It is argued that resolution-enhancement methods used along with difference spectra provide more detailed insights into the conformational changes occurring between photocycle intermediates.
Lazarova
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Departament de Bioquímica i de Biologia Molecular, Facultat de Medicina, Universitat Autònoma de Barcelona, Spain.
Padrós
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D000577:Amides / Q000737:chemistry; D001436:Bacteriorhodopsins / Q000737:chemistry* / Q000528:radiation effects; D006217:Halobacterium / Q000737:chemistry; D008027:Light; D017433:Protein Structure, Secondary / Q000528:radiation effects*; D017550:Spectroscopy, Fourier Transform Infrared
D000577:Amides; D001436:Bacteriorhodopsins