title: Astaxanthin binding and structural stability of the apple snail carotenoprotein ovorubin.
abstract: Ovorubin (OR) is the major perivitellin of the eggs of Pomacea canaliculata. The astaxanthin (ASX) binding and structural stability of OR were investigated by fluorescence spectroscopy and circular dichroism (CD). The apo-OR (without astaxanthin) shows a single, high affinity binding site for ASX (K(D)=0.5 microM). The quenching of tryptophan fluorescence by ASX indicates that about 22% are near the carotenoid-binding site in a non-polar environment, as indicated by tryptophan resonance energy transfer to the ligand. Secondary structure (alpha+beta) was virtually not affected by cofactor removal. Holo-OR shows unusually high thermal stability. The removal of ASX does not affect the thermal or chemical stability of the quaternary structure. In conclusion, although subtle changes were observed, ASX is not essential for OR stability, unlike most invertebrate carotenoproteins. This supports the idea that OR plays an important physiological role in the storage, transport and protection of carotenoids during snail embryogenesis.
authors.affiliation: Instituto de Investigaciones Bioquímicas de La Plata (INIBIOLP), CONICET-UNLP, La Plata, Argentina.
authors.forename: Marcos S
authors.initials: MS
authors.lastname: Dreon
authors.forename: Marcelo
authors.initials: M
authors.lastname: Ceolín
authors.forename: Horacio
authors.initials: H
authors.lastname: Heras
mesh_terms: D000818:Animals; D001059:Apoproteins / Q000737:chemistry / Q000378:metabolism; D001665:Binding Sites; D002942:Circular Dichroism; D004527:Egg Proteins / Q000737:chemistry* / Q000378:metabolism*; D011489:Protein Denaturation; D017433:Protein Structure, Secondary; D012908:Snails / Q000502:physiology; D013050:Spectrometry, Fluorescence; D013696:Temperature; D024341:Xanthophylls / Q000378:metabolism
chemical_list: D001059:Apoproteins; D004527:Egg Proteins; D024341:Xanthophylls; C002008:ovorubin; C005948:astaxanthine