Human ocular carotenoid-binding proteins.

Area of Science:

• Ophthalmology
• Biochemistry
• Nutritional Science

Background:

• Lutein and zeaxanthin are dietary carotenoids concentrated in the human macula.
• Selective tissue uptake suggests the involvement of specific binding proteins.

Purpose of the Study:

• To review the identification and characterization of carotenoid-binding proteins in the human retina.
• To propose a pathway for macular pigment carotenoid delivery involving these proteins.

Main Methods:

• Purification and characterization of carotenoid-binding proteins from human retina.
• Identification of glutathione S-transferase pi 1 (GSTP1) as a zeaxanthin-binding protein.
• Identification of a steroidogenic acute regulatory (StARD) domain protein as a lutein-binding protein.
• Characterization of tubulin as a high-capacity carotenoid-binding site.

Main Results:

• Several carotenoid-binding proteins have been identified in the human retina.
• Glutathione S-transferase pi 1 (GSTP1) specifically binds zeaxanthin.
• A steroidogenic acute regulatory (StARD) domain protein binds lutein.
• Tubulin serves as a non-specific, high-capacity carotenoid-binding protein.

Conclusions:

• Specific proteins, including GSTP1, StARD proteins, and tubulin, are involved in the selective uptake and deposition of lutein and zeaxanthin in the macula.
• A proposed pathway integrates serum lipoproteins and scavenger receptors for carotenoid delivery to the retina.