title: Identification and characterization of a Pi isoform of glutathione S-transferase (GSTP1) as a zeaxanthin-binding protein in the macula of the human eye.
abstract: Uptake, metabolism, and stabilization of xanthophyll carotenoids in the retina are thought to be mediated by specific xanthophyll-binding proteins (XBPs). A membrane-associated XBP was purified from human macula using ion-exchange chromatography followed by gel-exclusion chromatography. Two-dimensional gel electrophoresis showed a prominent spot of 23 kDa and an isoelectric point of 5.7. Using mass spectral sequencing methods and the public NCBI database, it was identified as a Pi isoform of human glutathione S-transferase (GSTP1). Dietary (3R,3'R)-zeaxanthin displayed the highest affinity with an apparent Kd of 0.33 microm, followed by (3R,3'S-meso)-zeaxanthin with an apparent Kd of 0.52 microm. (3R,3'R,6'R)-Lutein did not display any high-affinity binding to GSTP1. Other human recombinant glutathione S-transferase (GST) proteins, GSTA1 and GSTM1, exhibited only low affinity binding of xanthophylls. (3R,3'S-meso)-Zeaxanthin, an optically inactive nondietary xanthophyll carotenoid present in the human macula, exhibited a strong induced CD spectrum in association with human macular XBP that was nearly identical to the CD spectrum induced by GSTP1. Like-wise, dietary (3R,3'R)-zeaxanthin displayed alterations in its CD spectrum in association with GSTP1 and XBP. Other mammalian xanthophyll carrier proteins such as tubulin, high-density lipoprotein, low-density lipoprotein, albumin, and beta-lactoglobulin did not bind zeaxanthins with high affinity, and they failed to induce or alter xanthophyll CD spectra to any significant extent. Immunocytochemistry with an antibody to GSTP1 on human macula sections showed highest labeling in the outer and inner plexiform layers. These results indicate that GSTP1 is a specific XBP in human macula that interacts with (3R,3'S-meso)-zeaxanthin and dietary (3R,3'R)-zeaxanthin in contrast to apparently weaker interactions with (3R,3'R,6'R)-lutein.
authors.affiliation: Department of Ophthalmology and Visual Sciences, Moran Eye Center, University of Utah School of Medicine, Salt Lake City, Utah 84132, USA.
authors.forename: Prakash
authors.initials: P
authors.lastname: Bhosale
authors.forename: Alexander J
authors.initials: AJ
authors.lastname: Larson
authors.forename: Jeanne M
authors.initials: JM
authors.lastname: Frederick
authors.forename: Katie
authors.initials: K
authors.lastname: Southwick
authors.forename: Craig D
authors.initials: CD
authors.lastname: Thulin
authors.forename: Paul S
authors.initials: PS
authors.lastname: Bernstein
mesh_terms: D000328:Adult; D002338:Carotenoids / Q000737:chemistry; D002850:Chromatography, Gel; D002851:Chromatography, High Pressure Liquid; D002852:Chromatography, Ion Exchange; D002942:Circular Dichroism; D019992:Databases as Topic; D015180:Electrophoresis, Gel, Two-Dimensional; D051549:Glutathione S-Transferase pi; D005982:Glutathione Transferase / Q000737:chemistry* / Q000378:metabolism; D006801:Humans; D007150:Immunohistochemistry; D007525:Isoelectric Focusing; D007527:Isoenzymes / Q000737:chemistry* / Q000378:metabolism; D007700:Kinetics; D014975:Lutein / Q000737:chemistry*; D008266:Macula Lutea / Q000378:metabolism*; D013058:Mass Spectrometry; D008956:Models, Chemical; D011485:Protein Binding; D020033:Protein Isoforms; D011994:Recombinant Proteins / Q000737:chemistry; D013696:Temperature; D014461:Ultracentrifugation; D024341:Xanthophylls; D065146:Zeaxanthins; D019207:beta Carotene / Q000031:analogs & derivatives* / Q000737:chemistry*
chemical_list: D007527:Isoenzymes; D020033:Protein Isoforms; D011994:Recombinant Proteins; D024341:Xanthophylls; D065146:Zeaxanthins; D019207:beta Carotene; D002338:Carotenoids; C584722:meso-zeaxanthin; C496556:GSTP1 protein, human; D051549:Glutathione S-Transferase pi; D005982:Glutathione Transferase; D014975:Lutein