Study of Xanthorhodopsin, the Retinal-Protein Proton Pump of Salinibacter ruber with Light-Harvesting Carotenoid Antenna
Abstract
The project produced initial characterization of xanthorhodopsin, a novel carotenoid/retinal protein complex from the extremely halophilic eubacterium Salinibacter ruber, which functions as a light-driven proton pump. Its unique feature is a light-harvesting antenna, not found in any other retinal-based pumps. Fluorescence studies showed that 45% of light quanta absorbed by the carotenoid salinixanthin is transferred to retinal and used for transmembrane proton transport to energize ATP synthesis in the cells. The energy transfer occurs from extremely short lived (64 femtosecond) excited state of the carotenoid S2 to the S1 state of the retinal. From spectroscopic and x-ray studies that produced a 1.9 Angstom resolution structure, important information was obtained on the location of the carotenoid in the protein and its interaction with the retinal. The structure also revealed a number of unexpected features in the arrangement of the proton conducting pathways, not seen in the archaeal pumps, bacteriorhodopsin and archaerhodopsin. Particularly significant is a strongly hydrogen bonded Asp-His pair as the counterion to the retinal Schiff base, and a large cleft that extends deep into the protein at the extracellular side. It is likely that these features are common to other bacterial pumps, the proteorhodopsins, which still lack crystallographic information.
Document Details
- Document Type
- Technical Report
- Publication Date
- Mar 19, 2009
- Accession Number
- ADA500608
Entities
People
- J. K. Lanyi
- S. P. Balashov
Organizations
- University of California, Irvine