Vertebrate and invertebrate carotenoid-binding proteins

Abstract

In invertebrates and vertebrates, carotenoids are ubiquitous colorants, antioxidants, and provitamin A compounds that must be absorbed from dietary sources and transported to target tissues where they are taken up and stabilized to perform their physiological functions. These processes occur in a specific and regulated manner mediated by high-affinity carotenoid-binding proteins. In this mini-review, we examine the published literature on carotenoid-binding proteins in vertebrate and invertebrate systems, and we report our initial purification and characterization of a novel lutein-binding protein isolated from liver of Japanese quail (Coturnix japonica).

Figures

Fig. 1

Absorption spectrum of endogenous lutein bound to purified qlLBP. The top figure is the photodiode array chromatogram at the final step of purification on a gel filtration column. In the bottom figure, the absorption spectrum of purified qlLBP at 13 minutes retention time is compared to lutein and zeaxanthin dissolved in elution buffer containing CHAPS detergent.

Fig. 2

A. SDS-PAGE of qlLBP purified from quail liver. 10 μg of purified qlLBP was dissolved in 20 ml of TRIS buffer and loaded on to a 4–20% SDS-polyacrylamide gel for electrophoresis. Later, the gel was stained using Sypro Ruby from Bio-Rad to visualize the protein bands. B. Isoelectric focusing and gel electrophoresis. An aliquot of purified qlLBP was subjected to isoelectric focusing (IEF, pH 3–10) and SDS-PAGE analysis on a 4–20 % gel. Following the run, protein spots were stained with fluorescent Sypro Ruby protein stain. Gels were then visualized using a UV light source.

Fig 3

Binding study of partially purified qlLBP with lutein (n=3). Ten μl of concentrated (3R, 3′R, 6′R)-lutein dissolved in THF were added to 490 μl of 50 mM Tris-CHAPS (8 mM) buffer containing 1 μg of protein. After brief mixing, the mixtures were incubated overnight (16 h) at 4 °C. Unbound carotenoids were removed by four cycles of extraction with 200 μl of hexane (Kd=0.52 μM).