Chromophore-Anion Interactions in Halorhodopsin from Natronobacterium pharaonis Probed by Time-Resolved Resonance Raman Spectroscopy

详细信息    查看全文

• 作者：Sandra Gerscher ; Muthusamy Mylrajan ; Peter Hildebrandt ; Marie-Hé ; l&egrave ; ne Baron ; Renate Mü ; ller ; and Martin Engelhard
• 刊名：Biochemistry
• 出版年：1997
• 出版时间：September 9, 1997
• 年：1997
• 卷：36
• 期：36
• 页码：11012 - 11020
• 全文大小：208K
• 年卷期：v.36,no.36(September 9, 1997)
• ISSN：1520-4995

文摘

Halorhodopsin of Natronobacterium pharaoniswhich acts as a light-driven chloride pump isstudied by time-resolved resonance Raman spectroscopy. Insingle-beam experiments, resonance Ramanspectra were obtained of the parent state HR₅₇₈ and thefirst thermal intermediate HR₅₂₀. The parentstateis structural heterogeneous including ca. 80% all-trans and20% 13-cis isomers. The resonanceRamanspectra indicate that the all-trans conformer exhibitsessentially the same chromophoric structure as inthe parent states of bacteriorhodopsin or halorhodopsin fromHalobacterium salinarium. Specialemphasisof the resonance Raman spectroscopic analysis was laid on the C=C andC=N stretching region in orderto probe the interactions between the protonated Schiff base andvarious bound anions (chloride, bromide,iodide). These investigations were paralleled by spectroscopicstudies of retinal Schiff base modelcomplexes in different solvents in an attempt to determine the variousparameters which control the C=Cand C=N stretching frequencies. From these data, it wasconcluded that in the parent state the anion isnot involved in hydrogen bonding interactions with the Schiff baseproton but is presumably bound to anearby (positively charged) amino acid residue. On the other hand,the anion still exerts an appreciableeffect on the chromophore structure which is, for instance, reflectedby the variation of the isomercomposition in the presence of different anions and in theanion-depleted form. In contrast to the parentstate, the intermediate HR₅₂₀ reveals frequency shifts ofthe C=N stretching in the presence of differentanions. These findings indicate a closer proximity of the boundanion to the Schiff base proton which issufficient for hydrogen bonding interactions. These changes of theanion-chromophore interaction upontransition from HR₅₇₈ to HR₅₂₀ may be relatedto the coupling of the chromophore movement with theanion translocation.