Retinal-salinixanthin interactions in xanthorhodopsin: [corrected] a circular dichroism (CD) spectroscopy study with artificial pigments.
Xanthorhodopsin (xR) is a recently discovered retinal protein that contains, in addition to the retinal chromophore, a carotenoid (salinixanthin) absorbing at 456, 486, and 520 nm, which functions as a light-harvesting antenna. We have studied the interactions between the two chromophores by monitoring the absorbance and circular dichroism (CD) spectroscopies of artificial pigments derived from synthetic retinal analogues characterized by shifted absorption maxima. In addition, we have followed the binding process of the synthetic chromophores to the apomembrane of xR. We have revealed that the CD spectrum of xR originated mainly from the carotenoid chromophore without a significant contribution of the retinal chromophore. Because the binding process rate of these analogues is slower compared to all-trans retinal, it was possible to detect and analyze the major alterations in the CD spectrum. It was revealed that the main changes occur as a result of binding site occupation by the retinal chromophore and not because of the formation of the retinal-protein covalent bond.
Smolensky
Elena
E
Department of Organic Chemistry, Weizmann Institute of Science, Rehovot 76100, Israel.
Sheves
Mordechai
M
D000042:Absorption; D001426:Bacterial Proteins / Q000378:metabolism*; D001665:Binding Sites; D032701:Biomimetics; D002338:Carotenoids / Q000737:chemistry / Q000378:metabolism*; D002942:Circular Dichroism; D006027:Glycosides / Q000737:chemistry / Q000378:metabolism*; D008968:Molecular Conformation; D011485:Protein Binding; D017494:Proton Pumps / Q000378:metabolism*; D012172:Retinaldehyde / Q000737:chemistry / Q000378:metabolism*; D045249:Sphingobacterium; D013237:Stereoisomerism
D001426:Bacterial Proteins; D006027:Glycosides; D017494:Proton Pumps; C470489:salinixanthin; D002338:Carotenoids; D012172:Retinaldehyde