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Comparative characterization of two GDP-mannose dehydrogenase genes from Saccharina japonica (Laminariales, Phaeophyceae).

ABSTRACT: Saccharina japonica is an important commercial brown seaweed, its main product is alginate, which is used in food, textile and by the cosmetic and pharmaceutical industries. GDP-mannose dehydrogenase (GMD) is the key enzyme involved in the synthesis of alginate. However, little is known about GMD in S. japonica. Here we report comparative biochemical analysis of two GMD genes in S. japonica.Two GMD genes from S. japonica (Sjgmd1, Sjgmd2) were cloned. The open reading frame lengths of Sjgmd1, Sjgmd2 are 963 bp and 948 bp, respectively. Alignment analysis showed that the two SjGMD sequences shared 79.38 % identity. Both proteins possess the GGxCLPKDV and GxGxVG sequence motifs characteristic of the short-chain dehydrogenase/reductase superfamily. The optimum temperatures for SjGMDs were 30 °C (SjGMD1) and 20 °C (SjGMD2), and the optimum pH values were 8.0 (SjGMD1) and 8.25 (SjGMD2). Kinetic analysis demonstrated the Km values for the substrate GDP-mannose were 289 ?M (SjGMD1) and 177 ?M (SjGMD2), and the Km values for the cofactor NAD(+) were 139 ?M (SjGMD1) and 195 ?M (SjGMD2). The metal iron Zn(2+) is a potent inhibitor of SjGMD1 and SjGMD2. Real-time PCR analysis showed that heat and desiccation treatments resulted in a significant increase in Sjgmd1 and Sjgmd2 transcript abundance, suggesting that the SjGMDs are directly involved in the acclimitisation of S. japonica to abiotic stresses.Our work identified two novel genes encoding GMD in S. japonica, comparatively characterized their structural characteristics and enzyme kinetics, and revealed the function of GMD in the stress adaptability of S. japonica. The knowledge obtained here enriched our understanding of the alginate synthesis mechanism in S. japonica, and may promote further research on functional differences between GMD genes.

SUBMITTER: Zhang P

PROVIDER: S-EPMC4782291 | biostudies-literature | 2016 Mar

REPOSITORIES: biostudies-literature

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Comparative characterization of two GDP-mannose dehydrogenase genes from Saccharina japonica (Laminariales, Phaeophyceae).

Zhang Pengyan P Shao Zhanru Z Jin Weihua W Duan Delin D

BMC plant biology 20160308

<h4>Background</h4>Saccharina japonica is an important commercial brown seaweed, its main product is alginate, which is used in food, textile and by the cosmetic and pharmaceutical industries. GDP-mannose dehydrogenase (GMD) is the key enzyme involved in the synthesis of alginate. However, little is known about GMD in S. japonica. Here we report comparative biochemical analysis of two GMD genes in S. japonica.<h4>Results</h4>Two GMD genes from S. japonica (Sjgmd1, Sjgmd2) were cloned. The open r ...[more]

PMID: 26956020

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Project description:BackgroundBrown macroalgae dominate temperate coastal ecosystems, and their productivity is typically limited by nitrate availability. As an economically important kelp, Saccharina japonica is the most productive farmed seaweed and needs to be supplemented with sufficient nitrate throughout the cultivation process. However, molecular characterization of genes involved in nitrogen assimilation has not been conducted in brown macroalgae.ResultsHere, we described the identification of the nitrate reductase (NR) gene from S. japonica (SjNR). Using two different cloning methods for SjNR, i.e. rapid amplification of cDNA ends (RACE) and cDNA cloning alone, a single fragment was obtained respectively. According to results of sequence analysis between these two fragments, the tentative coding sequence in two clones, SjNR-L and SjNR-S, were suggested to represent two transcripts of the single copy SjNR, and the ATG of SjNR-S was located inside the third exon of SjNR-L. In the 5' upstream sequence of each transcript, promoter core elements, response elements, especially multiple N response elements which occurred in microalgal NR, were all predicted. Further sequence analysis revealed that both transcripts encoded all five domains conserved in eukaryotic plant NRs. RT-qPCR results showed that the transcription level of SjNR in juvenile sporophytes could be significantly induced by nitrate and inhibited by ammonium, which was in line with plant NRs. The recombinant SjNR-L and SjNR-S were all proved to have NR activity, suggesting that the single-copy gene SjNR might be regulated on transcription level based on alternative promoters and multiple transcriptional start sites. Moreover, both NADH and NADPH were found to be able to act as electron donors for SjNR alone, which is the first confirmation that brown algal NR has a NAD(P)H-bispecific form.ConclusionThese results will provide a scientific basis for understanding the N demand of kelp in various stages of cultivation and evaluating the environmental remediation potential of kelp in eutrophic sea areas.

Dataset Information

Comparative characterization of two GDP-mannose dehydrogenase genes from Saccharina japonica (Laminariales, Phaeophyceae).

Publications

Comparative characterization of two GDP-mannose dehydrogenase genes from Saccharina japonica (Laminariales, Phaeophyceae).

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