Structure of a prasinoxanthin-chlorophyll [formula omitted] light-harvesting complex of the green flagellate Pseudoscourfieldia marina (Micromonadophyceae)

Abstract

A light-harvesting complex was isolated from thylakoid membranes of the marine green flagellate Pseudoscourfieldia marina by sucrose density gradient centrifugation in the presence of the detergent n-dodecyl β- d-maltoside, followed by DEAE-cellulose ion-exchange chromatography. Absorption and fluorescence spectroscopy indicated that the complex was intact and capable of transferring energy from accessory pigments to chlorophyll a. The light-harvesting complex contained one major and two minor polypeptides with apparent molecular masses of 24 kDa, 26 kDa and 23 kDa, and the pigments chlorophyll a, chlorophyll b, prasinoxanthin, neoxanthin, magnesium 2,4-divinyl phaeoporphyrin a 5 monomethyl ester and one unknown carotenoid. Protein and pigment quantification indicated that one polypeptide is complexed with about 2.7 chlorophyll b, 1.8 chlorophyll a, 1.6 prasinoxanthin, 0.7 neoxanthin, 0.5 magnesium 2,4-divinyl phaeoporphyrin a 5 monomethyl ester and 0.2 unknown carotenoid. Immunoblot analysis demonstrated that the polypeptides of the light-harvesting complex of P. marina are structurally similar to those of Mantoniella gilva and other members of the Mamiellales, all of which possess the pigments prasinoxanthin and magnesium 2,4-divinyl phaeoporphyrin a 5 monomethyl ester.