Structural Variety of Bacteriorhodopsin
Bacteriorhodopsin (bR), the only protein contained in the purple membrane of Halobacterium halobium, functions as a light-driven proton pump. Such function must result from a series of concerted changes in conformation, microenvironments, and deprotonation/protonation of both the visible chromophore (retinylidene Schiff base) and the protein (opsin) during a photocycle. The aim of our ultraviolet resonance Raman (UVRR) study on bR is to obtain information on the dynamic structure of opsin during the photocycle. UVRR spectroscopy is a powerful technique for examining the structure of proteins [1–3]. Aromatic sidechains and mainchains in proteins absorb deep ultraviolet light and their vibrational scattering can be selectively enhanced by choosing appropriate excitation wavelengths. It is applicable to bR films as well as aqueous suspensions and possible structural differences between them can be detected. This technique has recently been applied to bR suspensions, the reported spectra being partly controversial [4–6], In the present study (1) suspension UVRR spectra of bR from different batches were examined and two types of bR, containing and not containing a tyrosinate were identified; (2) film UVRR spectra were compared with those of the aqueous suspensions and structural differences in the mainchain and tyrosine and tryptophan sidechains were observed; and (3) a 240-nm spectrum of a photocycle intermediate K was obtained and a slight change from bR568 in the tryptophan scattering was noticed.
KeywordsAqueous Suspension Purple Membrane Hydrated Film Potassium Sulfate Concerted Change
Unable to display preview. Download preview PDF.
- 1.I. Harada and H. Takeuchi, in Spectroscopy of Biological Systems, ed. by R. J. H. Clark and R. E. Hester (Wiley, Chichester, 1986), Chap, 3.Google Scholar
- 5.A. V. Feofanov, R. G. Efremov, and I. R. Nabiev, in XII International Conference on Raman Spectroscopy, ed. by J. R. Durig and J. F. Sullivan (Wiley, Chichester, 1990), pp. 544–545.Google Scholar