SPIN-LABELING ANALYSIS OF STRUCTURE AND DYNAMICS IN OCTOPUS RHODOPSIN

The location of cysteines accessible in octopus rhodopsin were charact erized by a spin-labeling technique. Two cysteines were found to bind a methanthiosulfonate spin label. One of the spin labels is attached t o helix V with the side chain located within the membrane, most probab ly close to the polar head group region. The second spin label was fou nd to be attached to cysteine 345 in the C terminus. Light-induced rev ersible electron paramagnetic resonance spectral changes were observed for the spin label attached at position 345. It is concluded that con formational changes occur during the rhodopsin to metarhodopsin transi tion in the vicinity of the C-terminus position 345.