Palmitoylation of Metazoan Carotenoid Oxygenases.

Sheetal Uppal,Eugenia Poliakov,Igor B Rogozin,T.Michael Redmond

doi:10.3390/molecules25081942

Abstract

Abundant in nature, carotenoids are a class of fat-soluble pigments with a polyene tetraterpenoid structure. They possess antioxidant properties and their consumption leads to certain health benefits in humans. Carotenoid cleavage oxygenases (CCOs) are a superfamily of enzymes which oxidatively cleave carotenoids and they are present in all kingdoms of life. Complexity of CCO evolution is high. For example, in this study we serendipitously found a new family of eukaryotic CCOs, the apocarotenoid oxygenase-like (ACOL) family. This family has several members in animal genomes and lacks the animal-specific amino acid motif PDPCK. This motif is likely to be associated with palmitoylation of some animal CCOs. We recently demonstrated that two mammalian members of the carotenoid oxygenase family retinal pigment epithelial-specific 65 kDa protein (RPE65) and beta-carotene oxygenase 2 (BCO2) are palmitoylated proteins. Here we used the acyl-resin-assisted capture (acyl-RAC) method to demonstrate protein palmitoylation and immunochemistry to localize mouse BCO2 (mBCO2) in COS7 cell line in the absence and presence of its substrate β-carotene. We demonstrate that mBCO2 palmitoylation depends on the evolutionarily conserved motif PDPCK and that metazoan family members lacking the motif (Lancelet beta-carotene oxygenase-like protein (BCOL) and Acropora ACOL) are not palmitoylated. Additionally, we observed that the palmitoylation status of mBCO2 and its membrane association depend on the presence of its substrate β-carotene. Based on our results we conclude that most metazoan carotenoid oxygenases retain the evolutionarily conserved palmitoylation PDPCK motif to target proteins to internal membranes depending on substrate status. Exceptions are in the secreted BCOL subfamily and the strictly cytosolic ancient ACOL subfamily of carotenoid oxygenases.

Highlights

Carotenoids are a class of naturally occurring pigments with antioxidant properties [1,2,3].β-Carotene and certain other carotenoids such as β-cryptoxanthin have provitamin A activity, and the hydroxylated carotenoid xanthophylls lutein and zeaxanthin have been shown to protect the retina of the eye against oxidative stress [4]
We demonstrate that PDPCK is a palmitoylation motif of beta-carotene oxygenase 2 (BCO2) and that, similar to retinal pigment epithelial-specific 65 kDa protein (RPE65), BCO2 palmitoylation depends on the presence of substrate
We describe a further example of S-palmitoylation post-translational modification (PTM) in the metazoan Carotenoid cleavage oxygenases (CCOs) family

Summary

Introduction

Carotenoids are a class of naturally occurring pigments with antioxidant properties [1,2,3].β-Carotene and certain other carotenoids such as β-cryptoxanthin have provitamin A activity, and the hydroxylated carotenoid xanthophylls lutein and zeaxanthin have been shown to protect the retina of the eye against oxidative stress [4]. Carotenoid oxygenases are present in all kingdoms of life and have only been rarely lost in animal genomes [12] They contain the same basic structural fold of a seven-bladed β-propeller and iron cofactor coordinated by four conserved histidines. RPE65 retinoid isomerase is an enzyme which plays a crucial role in the regeneration of 11-cis-retinal (visual chromophore of rhodopsin) in the visual cycle of the retina [18,20,21]. It is a divergent and atypical CCO in that it neither uses carotenoids as a substrate, nor is it an oxygenase. Mutation of C112 to any other residue leads to a complete loss of RPE65 activity [13,22,23]

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Conclusion