GSTP1-mediated zeaxanthin deposition underlies the skin pigmentation improvement induced by dietary corn gluten meal in yellow catfish

Abnormal pigmentation compromises the commercial value of aquatic products. However, the mechanism of pigment deposition in fish remains elusive. This study employs corn gluten meal (CGM) as a natural source to elucidate the deposition mechanism of key pigment(s) in yellow catfish. We demonstrated that inclusion of 20% CGM with 0.6% lysine in feed significantly improved the yellow-blue axis and chroma values in the dorsal and abdominal skin (P < 0.05). Metabolic analysis showed that CGM significantly increased the zeaxanthin and lutein deposition in yellow catfish skin (P < 0.05), with zeaxanthin/zeaxanthin palmitate exhibited the highest increase (P < 0.001). Using pure carotenoids as pigment sources, we illustrated that zeaxanthin deposition was sufficient to improve the yellow-blue axis and chroma values in the dorsal and abdominal skin of yellow catfish (P < 0.05). Combining RNA-seq data, we discovered that CGM significantly increased skin apolipoprotein E (ApoE) and glutathione S-transferase Pi 1 (GSTP1) protein levels (27% rise, P < 0.05). The affinity assays further revealed zeaxanthin was transported by ApoE to binding GSTP1, as reflected by a 1.11 °C increase in the protein denaturation temperature of GSTP1. We therefore elucidate the mechanism for pigment deposition in the skin of yellow catfish and provide the accurate target for improving the appearance quality of aquatic products.