Heterologous Production of 2,2′-Dihydroxy Derivatives of Astaxanthin and Adonirubin in Escherichia coli and Evaluation of Their Antioxidant Activity

Astaxanthin is a prominent carotenoid with strong antioxidant activity due to its 13 conjugated double bonds and its 3,3'-hydroxy groups adjacent to its 4,4'-carbonyl groups. This red pigment is utilized as a food additive and nutritional supplement, and it also has applications in cosmetics. But the extremely low water solubility of astaxanthin limits its broader commercial application. In order to decrease the hydrophobic property of astaxanthin, we produced 2,2'-dihydroxy derivatives of astaxanthin and its intermediate adonirubin, (2<i>R</i>,3<i>S</i>,2'<i>R</i>,3'<i>S</i>)-2,2'-dihydroxyastaxanthin (<b>1</b>) and (2<i>R,3S,</i>2'<i>R</i>)<i>-</i>2,2'-dihydoxyadonirubin (<b>2</b>), in the cells of <i>Escherichia coli</i> as dominant carotenoids. This result was achieved by using the <i>crtG</i> gene that codes for zeaxanthin/canthaxanthin/astaxanthin 2,2'-hydroxylase, derived from <i>Brevundimonas</i> sp. strain SD212, in addition to astaxanthin biosynthesis genes that carry the <i>Haematococcus pluvialis IDI</i>, <i>Pantoea ananatis crtE</i>, <i>crtB</i>, <i>crtI</i>, <i>crtY</i>, <i>crtZ</i>, and <i>Paracoccus</i> sp. N81106 <i>crtW</i> genes. The singlet oxygen-quenching activities of <b>1</b> and <b>2</b> (IC₅₀ 4.3 μM and 8.3 μM, respectively) were examined and found to be comparable to that of astaxanthin (IC₅₀ 1.7 μM).