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The mechanism exploration of the non‐colonic toxicity and obesity inhibition of food‐grade κ‐carrageenan by transcriptome

ABSTRACT: Abstract Previous study has suggested the colonic nontoxicity and obesity inhibition of food‐grade κ‐carrageenan in obese mice. Further study using transcriptome is important to provide further understanding on the gene expressions of inflammation and obesity. Here, the obese mice without any treatment (HFD) or with 5% food‐grade κ‐carrageenan diet intervention (H5%) were used to perform colonic transcriptome sequencing. The results showed that genes involved in the inflammatory pathways or tight junction protein encoding were not significantly dysregulated by 5% carrageenan. However, the expression of lipid metabolism genes meaningfully changed as evidenced by the decreased gene levels of adipocytokines, lipogenesis, lipid absorption and transport, and the increased adipolysis and oxidation. In addition, the carrageenan metabolism experiments by toluidine blue (TB) staining of colon and high‐performance size exclusion chromatography (HPSEC) of feces supernatant showed that the food‐grade κ‐carrageenan was not absorbed or significantly degraded in the digestive tract of obese mice. Hence, the fact that food‐grade κ‐carrageenan was not significantly metabolized by the organism and did not cause obvious dysregulation of colonic inflammatory genes provided evidences for its noncolonic toxicity in obese mice. An anti‐obesity potential of food‐grade κ‐carrageenan was probably mediated by the regulation of lipids metabolism‐related genes. In this study, we aimed to explore the mechanisms of carrageenan actions, and the obese mice with no treatment (HFD) or 5% food‐grade κ‐carrageenan intervention (H5%) were used to perform carrageenan metabolism experiments and colonic transcriptome sequencing. The toluidine blue (TB) staining of colon and high‐performance size exclusion chromatography (HPSEC) of feces supernatant showed that the food‐grade κ‐carrageenan was not absorbed or significantly degraded in the digestive tract of obese mice. The transcriptome sequencing showed that no genes involved in the inflammatory pathways or tight junction protein encoding were significantly dysregulated by 5% carrageenan. However, the expression of lipid metabolism genes meaningfully changed as evident by the decreased gene levels of adipocytokines, lipogenesis, along with absorption and transport, but increased adipolysis and oxidation.

SUBMITTER: Zhang H

PROVIDER: S-EPMC8565199 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Algal cell wall polysaccharides constitute a large fraction in the biomass of marine primary producers and are thus important in nutrient transfer between trophic levels in the marine ecosystem. In order for this transfer to take place, polysaccharides must be degraded into smaller mono- and disaccharide units, which are subsequently metabolized, and key components in this degradation are bacterial enzymes. The marine bacterium Colwellia echini A3T is a potent enzyme producer since it completely hydrolyzes agar and κ-carrageenan. Here, we report that the genome of C. echini A3T harbors two large gene clusters for the degradation of carrageenan and agar, respectively. Phylogenetical and functional studies combined with transcriptomics and in silico structural modeling revealed that the carrageenolytic cluster encodes furcellaranases, a new class of glycoside hydrolase family 16 (GH16) enzymes that are key enzymes for hydrolysis of furcellaran, a hybrid carrageenan containing both β- and κ-carrageenan motifs. We show that furcellaranases degrade furcellaran into neocarratetraose-43-O-monosulfate [DA-(α1,3)-G4S-(β1,4)-DA-(α1,3)-G], and we propose a molecular model of furcellaranases and compare the active site architectures of furcellaranases, κ-carrageenases, β-agarases, and β-porphyranases. Furthermore, C. echini A3T was shown to encode κ-carrageenases, ι-carrageenases, and members of a new class of enzymes, active only on hybrid β/κ-carrageenan tetrasaccharides. On the basis of our genomic, transcriptomic, and functional analyses of the carrageenolytic enzyme repertoire, we propose a new model for how C. echini A3T degrades complex sulfated marine polysaccharides such as furcellaran, κ-carrageenan, and ι-carrageenan.IMPORTANCE Here, we report that a recently described bacterium, Colwellia echini, harbors a large number of enzymes enabling the bacterium to grow on κ-carrageenan and agar. The genes are organized in two clusters that encode enzymes for the total degradation of κ-carrageenan and agar, respectively. As the first, we report on the structure/function relationship of a new class of enzymes that hydrolyze furcellaran, a partially sulfated β/κ-carrageenan. Using an in silico model, we hypothesize a molecular structure of furcellaranases and compare structural features and active site architectures of furcellaranases with those of other GH16 polysaccharide hydrolases, such as κ-carrageenases, β-agarases, and β-porphyranases. Furthermore, we describe a new class of enzymes distantly related to GH42 and GH160 β-galactosidases and show that this new class of enzymes is active only on hybrid β/κ-carrageenan oligosaccharides. Finally, we propose a new model for how the carrageenolytic enzyme repertoire enables C. echini to metabolize β/κ-, κ-, and ι-carrageenan.

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The mechanism exploration of the non‐colonic toxicity and obesity inhibition of food‐grade κ‐carrageenan by transcriptome

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