Spectral changes of the B800–850 antenna complex from Ectothiorhodospira sp. induced by detergent and salt treatment

Abstract

We have studied the effects of the detergent lauryl dimethylamine N-oxide and NaCl in the near infrared absorption spectra of the B800-850 antenna complex from Ectothiorhodospira sp. Strong spectral changes were induced on the BChl850 band by the lauryl dimethylamine N-oxide consisting of a blue shift, from 857 to 839-837 nm, and a hypochromism. No significant effects were detected on the BChl800 band in the same conditions. The changes were reversible after removing most of the detergent from the sample. Depending upon the detergent concentration in the solution, NaCl was also able to reverse the blueshift and increase the intensity of the 850 nm band close to the native values. Moreover, we have been able to separate both phenomena. Addition of 0.350 M NaCl after sample incubation with 0.15% (v/v) lauryl dimethylamine N-oxide for 30 min allowed a 9-10 nm redshift with no significant hyperchromism of the lowest energy band. We explained the overall effect of the detergent assuming that the lauryl dimethylamine N-oxide bound to the hydrophobic moiety of the complex and caused some protein conformational changes which affected the BChl850 domain without affecting that of the BChl800. The NaCl was able to circumvent these effects, most probably by acting directly on the BChl850 molecules or on the protein structure surrounding them.

Gene sequencing and characterization of the light-harvesting complex 2 from thermophilic purple sulfur bacterium Thermochromatium tepidum

“…Similar behavior was reported on the LH2 complexes from purple sulfur bacterium Ectothiorhodospira sp. (de Zarate and Picorel 1994) and purple nonsulfur bacterium Rhodovulum sulfidophilum (formerly Rhodobacter sulfidophilus) (Tadros et al 1995), where the blue shifts were observed only for the B850 band in LDAO solution, and NaCl was able to restore the spectra. Interaction between detergents and LH2 polypeptides can be confirmed from the crystal structures.…”

Wavelength Shifts Correlation between Near Infrared and Ultraviolet Regions of the LHII Bacteriochlorophyll Spectrum from Ectothiorhodospira sp.

“…As m entioned in the Introduction both LDAO (Ortiz de Zarate and Picorel, 1994) and alkaline pH (Buche and Picorel, 1998) induce a reversible blue shift of LHIIB850 from Ectothiorhodospira sp. Both treatm ents affect poorly the spectral properties of the complex in a wavelength range from the Soret band to B800.…”

“…B850 were reported (Ortiz de Zarate and Picorel, 1994;Buche and Picorel, 1998;Buche et al, 2000;Buche, 2000). The detergent LDAO generates a 19 nm blue shift of this band which was attributed to the loss of one or two H links (Ortiz de Zarate and Picorel, 1995).…”

“…was grown photosynthetically as de scribed by Lefebvre et al (1984). Preparations of the LHII antenna were obtained as described pre viously (Ortiz de Zarate and Picorel, 1994) with some modifications (Buche and Picorel, 1998). Several LHII preparations were then concentrated to obtain an optical density corresponding to an absorbance of 75 at 800 nm and under 1 cm path length.…”

“…B850 were recently described. The de tergent lauryldimethylamine N-oxide (LDAO) was reported as inducing a specific blue shift of B850 from 857 to 839-837 nm, and a hypochromism (Ortiz de Zarate and Picorel, 1994). This ef fect was correlated with a loss of one or two H links between BChl and polypeptides (Ortiz de Zarate, 1995).…”