All Three Human Scavenger Receptor Class B Proteins Can Bind and Transport all Three Macular Xanthophyll Carotenoids

Rajalekshmy S, et al. , , Arch Biochem Biophys., 2017

Plant carotenoids are important antioxidant molecules required in the human diet for multiple physiological functions and health benefits. The goal of this study was to identify the role of Scavenger Receptor Class B proteins (SRBs) in the uptake into circulation, and the transport and accumulation of xanthophyll carotenoids into retinal tissue. Using purified human proteins, a Pall Fortebio Pioneer was used to determine binding kinetics of three xanthophyll carotenoids (lutein, zeaxanthin, and mesozeaxanthin) to three SRBs (SR-B1, SR-B2, and CD36). All three SRBs were immobilized onto biosensors and were capable of binding the carotenoids at low micromolar affinities characteristic of transport proteins. Cell-based assays were then performed to examine the uptake of carotenoids by SRBs using a cell line overexpression system in SRB null cells (HEK-293T) compared to retinal cells endogenously expressing SRBs (ARPE19). Additionally, immunohistochemistry of human donor retinal tissue identified areas of carotenoid accumulation in different zones of retinal tissue.

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