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. 2023 Jan 4;21(1):42.
doi: 10.3390/md21010042.

The Polysaccharidic Nature of the Skeleton of Marennine as Determined by NMR Spectroscopy

Ilhem Zebiri  1 , Boris Jacquette  2 , Nellie Francezon  1   2 , Mickaël Herbaut  1   2 , Amina Latigui  2 , Sullivan Bricaud  2 , Réjean Tremblay  3 , Pamela Pasetto  2 , Jean-Luc Mouget  1 , Jens Dittmer  2
Affiliations

The Polysaccharidic Nature of the Skeleton of Marennine as Determined by NMR Spectroscopy

Ilhem Zebiri et al. Mar Drugs. .

Abstract

The water-soluble blue-green pigment marennine, produced and partly excreted by the diatom Haslea ostrearia, and known for a long time for its role in the greening of oysters, was isolated from the culture medium, purified, and analyzed by Nuclear Magnetic Resonance (NMR) in order to gain insight into its chemical structure. The spectra show mainly carbohydrates of a complex composition, apparently highly branched, and with a mass in the order of 10 kDa. There are, in addition, some signals of aliphatic and, much weaker, aromatic groups that present aglycons. The latter might be responsible for the color. These carbohydrates are always associated with the blue-green color and cannot be separated from it by most treatments; they are interpreted as constituting the frame of the pigment. NMR after hydrolysis identifies the most abundant monosaccharides in marennine as galactose, xylose, mannose, rhamnose, and fucose.

Keywords: Haslea ostrearia; biomolecular NMR; blue pigment; diatoms; marennine; microalgae; polysaccharides.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
(a) Diatom Haslea ostrearia with a concentration of marennine in the apices. (b) Solution of extracellular marennine (EMn) after initial purification by precipitation and re-solubilization in formic acid.
Figure 2
Figure 2
(a) 1H DOSY and (b) single pulse 1H spectrum of extracellular marennine (EMn) in D2O. The aromatic part is scaled up by a factor of 20 in (b). (c) 1H spectrum of intracellular marennine (IMn) and (d) hydrolyzed EMn.
Figure 3
Figure 3
COSY spectra of native (dark blue/blue) and hydrolyzed (dark red/red) external marennine EMn. The spectrum of hydrolyzed EMn is shifted by +0.12 ppm in both dimensions. Some assignments are indicated: blue: native, red: hydrolyzed and black: general regions.
Figure 4
Figure 4
(a) 1H and (b) 13C chemical shifts of two spin systems of hydrolyzed extracellular marennine EMn (red) compared with the literature values of α- and β-galactose taken from [34] (ref. 1, blue) and [30] (ref. 2, green). (c) J-couplings between neighboring hydrogens as estimated from the COSY peak patterns and hydrogen orientation (axial up, down, or equatorial) derived from them.
Figure 5
Figure 5
Anomeric region of a 13C DEPT spectrum of hydrolyzed extracellular marennine EMn. (n.a.: not assigned).
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