Protein dynamics of a light-driven Na⁺ pump rhodopsin probed using a tryptophan residue near the retinal chromophore

Abstract

Elucidation of protein conformational changes associated with ion transport in ion pumps is important for understanding the mechanism of their functions. We demonstrate the protein dynamics occurring during Na + transport in the light-driven Na + pump KR2 using time-resolved ultraviolet resonance Raman spectroscopy. The environment around Trp215 in the vicinity of the retinal chromophore becomes less hydrophobic during ion uptake and then returns to its original hydrophobic environment to prevent the backflow of Na + . These findings are consistent with the alternating-access model of ion pumps, indicating that our method is a powerful tool for elucidating ion transport mechanisms in ion pumps.

Impact of protein–chromophore interaction on the retinal excited state and photocycle of Gloeobacter rhodopsin: role of conserved tryptophan residues

“…Atomic contacts between the bulky side chain of Trp215 and the C 20 methyl group of the retinal chromophore promote relaxation of the RPSB from the 13-cis to the all-trans form in the light-driven outward Na + pump Krokinobacter rhodopsin 2 (KR2). 16 Timeresolved UVRR spectroscopy revealed that the environment around Trp215 becomes less hydrophobic at 1 ms aer photoirradiation, and recovers to the unphotolyzed state with a time constant of about 10 ms. 17 Recently, time-resolved absorption as well as Raman spectroscopic studies were employed to investigate the effect of ultrafast electric eld change on the photocycle of BR. The change in the aromatic residues induced by the high dipole moment of the retinal chromophore in BR was also observed in recent deep-UV femtosecond stimulated Raman spectroscopy.…”