X. Feng et al., Determination of a molecular torsional angle in the metarhodopsin-I photointermediate of rhodopsin by double-quantum solid-state NMR, J BIOM NMR, 16(1), 2000, pp. 1-8
We present a solid-state NMR study of metarhodopsin-I, the pre-discharge in
termediate of the photochemical signal transduction cascade of rhodopsin, w
hich is the 41 kDa integral membrane protein that triggers phototransductio
n in vertebrate rod cells. The H-C10-C11-H torsional angles of the retinyli
dene chromophore in bovine rhodopsin and metarhodopsin-I were determined si
multaneously in the photo-activated membrane-bound state, using double-quan
tum heteronuclear local field spectroscopy. The torsional angles were estim
ated to be |phi| = 160 +/- 10 degrees for rhodopsin and phi= 180 +/- 25 deg
rees for metarhodopsin-I. The result is consistent with current models of t
he photo-induced conformational transitions in the chromophore, in which th
e 11-Z retinal ground state is twisted, while the later photointermediates
have a planar all-E conformation.