On The Interactions Of Detergent And Lipids With LH2 Complexes Of Rhodobacter Azotoformans

LH2 complex is one of functional elements of the photosynthesis and is responsible for harvest and transmission of light energy, in the intracytoplasmic membrane (photosynthetic membranes) of photosynthetic bacteria, containing membrane protein, Bacteriochlorophyll and carotenoids. Surfactant as solvent widely used in purification, reconstruction and crystallization of LH2.It is very important to reveal the effect of Surfactant on structure and function of LH2.Membrane lipid is an important component of photosynthetic membranes for LH2 function to provide the basic framework, the study of the interaction between membrane lipids and LH2 for research of photosynthetic membrane structure and function and understanding of the nature of photosynthesis is important.In this paper, LH2 complexes of Rhodobacter azotoformans as the research object, using spectroscopic methods, combined with liposomes reconstruction and atomic force microscopy to study effect of the surfactant on the structure and function of LH2 and LH2 liposomes reconstruction and 2D observed crystal structure of LH2.Include the following results:1.Lauryl dimethylamine N-oxide(LDAO) detergent plays a vital role in purification,crystallization and biochemical properties of peripheral light-harvesting antenna(LH2) from purple bacteria. It is very important to reveal the effect of LDAO on structure and function of LH2.In the present paper,the effects of LDAO on the release behavior of bacteriochlorophyll (BChl) molecules and the conformation of the LH2 complexes from Rhodobacter azotoformans 134K20 were investigated in detailed by using spectroscopy. The results indicated that:(1)the conformation change of LH2 induced by LDAO at pH 8.0 result in the of content ofα-helix and the blue shift of absorption peak of Tyr and BChl-B850 molecules (B850) under room temperature,Moreover,energy transfer efficiency of LH2 was enhanced.(2) At 60℃,the BChl-B800 and-B850 molecules were released and transformed into free BChl at pH 8.0. More important, at high temperature,LDAO has capacity to stabilize LH2,slow down and change the release behavior of the B800 and B850. (3) In strong acid or strong alkalic solution,LDAO can accelerate the release speed of B800 and B850 from LH2 and improve transformation of B800 and B850 into bacteriopheophytin(BPhe) and free BChl,respectively. But their release behaviors are different, particularly in strong acid solution without LDAO,the B850 was released firstly and then self-assembled.2.The release behaviors of bacteriochlorophyll (BChl) of LH2 from Rhodobacter azotoformans induced by sodium dodecyl sulfate (SDS)were investigated using absorption spectroscopy. The results indicated that BChl-B800 (B800) are released from their binding sites and transformed into free BChl by incubating LH2 sample in 10 mmol·L-1 Tris-HCl (pH 8.0) buffer containing SDS of low concentration at room temperature. However, the BChl-B850 (B850) are not affected. The dynamics of B800 release and free BChl formation induced by 0.08%(w/v) SDS can be well fitted by the monoexponential model.The rate constant of B800 release is nearly equal to that of free BChl formation. The release of both B800 and B850 of LH2 can be induced by high concentration SDS,simultaneously.B800 can be completely transformed into free BChl,but not for B850.Although both of their release processes show monoexponential models in 1% SDS solution, the release rate constant of B850 is remarkably lower than that of B800 and close to that of free BChl formation.3.the 2D crystal structure of LH2 complex of Rhodobacter azotoformans were studied Using liposomes reconstruction and atomic force microscopy. The results showed that:by ultrasonic method and cyclic freezing and thawing method can be prepared by homogeneous particle size of about 100nm layer of soybean lecithin liposomes using dialysis liposomes can be realized with the LH2 complex reconstruction, reconstructed,B850 in the absorption and fluorescence spectra of the peaks are the blue shift. The tapping mode AFM can be used to observe good liposomes LH2 complex, Rhodobacter azotoformans LH2 was hollow cylinder, a diameter of about 4nm; by cholesterol and phosphatidylethanolamine(1:10,w/w) mixture, and hydration medium containing glucose and sucrose, after ultrasound PE liposomes were prepared4.Aggregation behaviors of photosynthetic pigments in aqueous solution were investigated by using absorption spectroscopy. The results show that in aqueous solution under room temperature, BChl of photosynthetic pigments form two different aggregation states, showing a significant red shift of BChl Qy band and into two peaks. Lower temperature helps to keep the two aggregation states,higher temperatures lead to the aggregation state of the two together transform into another aggregation state. Reduce the water content or adding surfactant can disaggregation of BChl aggregate state transform into BChl monomer.