TAILIEUCHUNG - Báo cáo khoa học: Interconversions among four M-intermediates in the bacteriorhodopsin photocycle

Halobacterium salinarumdisplays four distinct kinetic forms of M-intermediate in its bacteriorhodopsin photocycle. In wild-type, there are mainly two species with time constants near 2 and 5 ms. Under various kinds of stress, two other species arise with time constants near 10 and 70 ms. We show that these four species are interconvertible. Increases in membrane hydrophobicity convert the slower to faster forms. Perturbations caused by Triton X-100 or mutations convert faster to slower forms. | Eur. J. Biochem. 270 3518-3524 2003 FEBS 2003 doi Interconversions among four M-intermediates in the bacteriorhodopsin photocycle Richard W. Hendler and Salil Bose Laboratory of Cell Biology National Heart Lung and Blood Institute National Institutes of Health Bethesda MD USA Halobacterium salinarum displays four distinct kinetic forms of M-intermediate in its bacteriorhodopsin photocycle. In wild-type there are mainly two species with time constants near 2 and 5 ms. Under various kinds of stress two other species arise with time constants near 10 and 70 ms. We show that these four species are interconvertible. Increases in membrane hydrophobicity convert the slower to faster forms. Perturbations caused by Triton X-100 or mutations convert faster to slower forms. The fastest form requires a hydrophobic membrane environment near a ring of four charged aspartate residues in the trimer namely Asp36 Asp38 Asp102 and Asp104 in the cytoplasmic loop regions. Interconversions of the 2-ms and 5-ms species of the wildtype are accomplished by pH-changes. The potential significance of these findings is discussed. Keywords enzyme control lipid-protein interactions membrane proteins proton pumps. Bacteriorhodopsin BR is a light-driven energy-transducing proton pump located in the cell membrane of Halobacteria for a review of its characteristics and history see 1 . It is generally agreed that there are five basic thermal intermediates in the BR photocycle namely K L M N and O. Previous work from this laboratory has led to the hypothesis that different kinetic and perhaps functional forms of the M-intermediate of the BR photocycle depend on local membrane lipid environments surrounding BR molecules reviewed in 2 . Only a brief summary of relevant details will be provided here. The basic findings are a Triton X-100 removes the fast M-intermediate Mf s w 2 ms decreases the amount of the slow M-intermediate Ms s w 5 ms and forms two new much .

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