TY - JOUR
T1 - X-ray crystal structures of diacetates of 6-s-cis and 6-s-trans astaxanthin and of 7,8-didehydroastaxanthin and 7,8,7′,8′- tetradehydroastaxanthin: Comparison with free and protein-bound asta-xanthins
AU - Bartalucci, Giuditta
AU - Fisher, Stuart
AU - Helliwell, John R.
AU - Helliwell, Madeleine
AU - Liaaen-Jensen, Synnve
AU - Warren, John E.
AU - Wilkinson, James
PY - 2009
Y1 - 2009
N2 - The crystal structures of the 6-s-cis [s-cis-(1)] and 6-s-trans [s-trans-(1)] conformers of the diacetates of astaxanthin (AXT) and those of (3S,3′S)-7,8-didehydroastaxanthin [(3S,3′S)-3,3′-dihydroxy-7, 8-didehydro-Β,Β-carotene-4,4′-dione (2)] and (3S,3′S)-7,8,7′,8′-tetradehydroastaxanthin [(3S,3′S)-3,3′-dihydroxy-7,8,7′,8′-tetradehydro-Β, Β-carotene-4, 4′-dione (3)] are reported. The conformations of these four molecules vary in particular with the angle of twist of the end rings out of the plane of the polyene chain; for s-cis-(1), the end rings are twisted out of the plane of the polyene chain by an angle of -49.0 (5)°, and the conformation is therefore similar to that found for unesterified AXT as well as for the carotenoids, canthaxanthin and Β,Β-carotene. For s-trans-(1), the end rings are coplanar with the polyene chain and its conformation is much more similar to that of the protein-bound AXT in the blue protein, crustacyanin, which is found in the shell of lobsters, although s-trans-(1) shows much less bowing of the polyene chain. In (2) and (3) the end rings are also almost coplanar with the polyene chain with the end rings in (2) in the s-cis conformation, and in (3) in the s-trans conformation. Thus, an extensive ensemble of the possible Β end-ring conformations has been determined. These structures are compared with one another as well as unbound, unesterified AXT and protein-bound AXT. Also, the effect of the end-ring conformations on the colour and UV-vis spectra of the crystals was established. © 2009 International Union of Crystallography.
AB - The crystal structures of the 6-s-cis [s-cis-(1)] and 6-s-trans [s-trans-(1)] conformers of the diacetates of astaxanthin (AXT) and those of (3S,3′S)-7,8-didehydroastaxanthin [(3S,3′S)-3,3′-dihydroxy-7, 8-didehydro-Β,Β-carotene-4,4′-dione (2)] and (3S,3′S)-7,8,7′,8′-tetradehydroastaxanthin [(3S,3′S)-3,3′-dihydroxy-7,8,7′,8′-tetradehydro-Β, Β-carotene-4, 4′-dione (3)] are reported. The conformations of these four molecules vary in particular with the angle of twist of the end rings out of the plane of the polyene chain; for s-cis-(1), the end rings are twisted out of the plane of the polyene chain by an angle of -49.0 (5)°, and the conformation is therefore similar to that found for unesterified AXT as well as for the carotenoids, canthaxanthin and Β,Β-carotene. For s-trans-(1), the end rings are coplanar with the polyene chain and its conformation is much more similar to that of the protein-bound AXT in the blue protein, crustacyanin, which is found in the shell of lobsters, although s-trans-(1) shows much less bowing of the polyene chain. In (2) and (3) the end rings are also almost coplanar with the polyene chain with the end rings in (2) in the s-cis conformation, and in (3) in the s-trans conformation. Thus, an extensive ensemble of the possible Β end-ring conformations has been determined. These structures are compared with one another as well as unbound, unesterified AXT and protein-bound AXT. Also, the effect of the end-ring conformations on the colour and UV-vis spectra of the crystals was established. © 2009 International Union of Crystallography.
KW - Astaxanthins (free and protein-bound)
KW - Bathochromic shift
KW - Carotenoids
KW - Conformation
KW - UV-vis spectroscopy
U2 - 10.1107/S0108768109004649
DO - 10.1107/S0108768109004649
M3 - Article
SN - 0108-7681
VL - 65
SP - 238
EP - 247
JO - Acta Crystallographica Section B: Structural Science
JF - Acta Crystallographica Section B: Structural Science
IS - 2
ER -