Spectroscopic Properties of LH2 from Thermochromatium tepidum in Liposome and Detergent Micelles†

doi:10.7503/cjcu20160277

Abstract

Abstract:

By the use of dynamic light scattering(DLS), transmission electron microscopy(TEM), UV-Vis and resonance Raman spectroscopy, the properties of LH2 from Thermochromatium(Tch.) tepidum in two detergent micelles and in liposome were studied, respectively. The results show that in LH2-liposome the conformation of spirilloxanthin, an incorporated longer chain carotenoid, is obviously different from that in detergent micelles. The charge state of the terminal groups of detergents or lipids is the key factor affecting the B850 absorption. Generally, the calcium ions cause red-shift of the B850 absorption and hyperchromicity, while the proton has the opposite effect. Based on the amino acid sequence analysis, several amino acid residues on the C-terminus of α apo-protein were proposed to constitute the potential binding site for the calcium ion and proton. Such Ca²⁺- and H⁺-regulated changes of B850 absorption might be an adaptive mechanism to the living environment for this species.

Key words: Thermochromatium tepidum, Peripheral antenna complex LH2, Detergent, Liposome

CLC Number:

O641

TrendMD:

HUO Yilin, SHI Ying, WANG Qinyue, LI Luoyuan, YU Longjiang, WANG Peng, ZHANG Jianping, WANG Zhengyu. Spectroscopic Properties of LH2 from Thermochromatium tepidum in Liposome and Detergent Micelles^†[J]. Chem. J. Chinese Universities, 2016, 37(9): 1678.

Figures/Tables 7

Fig.1 Absorption of LH2 from Tch. tepidum in various environments at pH=8 a. in DMM; b. in LDAO; c. in liposome. The arrow shows the absorption of spirilloxanthin.

Fig.2 TEM images of LH2 from Tch. tepidum in liposome(A), DDM(B) and LDAO(C) The samples were negatively stained with 1% uranium acetate.

Fig.3 DLS data of the LH2 from Tch. tepidum in various detergents micelles or liposome systems a. in DMM(106 nm/565 nm); b. in LDAO(14 nm/257 nm); c. in liposome(73 nm). The data in the corresponding parentheses are the Rh of the vesicles for each system.

Fig.4 Resonance Raman spectra of LH2 from Tch. tepidum in various environments under the excitation at 532 nm a. in DDM; b. in LDAO; c. in liposome.

Fig.5 Qy absorption comparison of LH2 from Tch. tepidum in 0.05% DDM(a), 0.1% LDAO(b) and PC(c) liposome, under pH=8(A, C) and 3(B, D), and without Ca2+(A, B) or with 200 mmol/L Ca2+(C, D)(all the spectra are normalized at 797 nm), respectively Arrows in (A) show the splitting peaks position of B800.

Table 1 Qy absorption characteristics of LH2 from Tch. tepidum under various conditionsa

System	Without Ca²⁺				With 200 mmol/L Ca²⁺
	pH=8		pH=3		pH=8		pH=3
	λ_{max, B850}/nm	OD_B850/OD_B800	λ_{max, B850}/nm	OD_B850/OD_B800	λ_{max, B850}/nm	OD_B850/OD_B800	λ_{max, B850}/nm	OD_B850/OD_B800
In DDM	855	1.41	854	1.28	857	1.53	855	1.35
In LDAO	845	0.96	845	0.90	854	1.32	843	1.02
In liposome	850	1.05	848	1.01	854	1.33	846	1.26
In chromatophore^b	854	1.41	852	1.18	858	1.38	857	1.32

Fig.6 Molecular structure and components of detergents(A, B) or lipid(C), molecular structure and components of lipids of chromatophore from Tch. Tepidum(D) and the amino acid sequence of α-apoproteins of LH2 from Tch. Tepidum[4](E) R1—R4 are the aliphatic chain with various length and degree of unsaturation. The gray broken line indicates the B850 bacteriochlorophyll binding histidine, and the red broken line indicates the possible binding points for calcium ion or proton.

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