Abstract
Methylation of one hydroxyl group of monosaccharides occurs in some bacteria, fungi, worms, molluscs, and also in plants. Although knowledge on the exact functions of this process is missing, methylation is an option to modulate glycan structures thereby leading to new biological activities. In plants, methylated monosaccharides are often present in minor amounts and, therefore, overseen in analytical investigations. A special difficulty is the distinction between 3-O-methyl- and 4-O-methyl-hexoses, due to similar fragmentation patterns of methylated alditol acetates in gas-chromatography with mass spectrometric detection and, in the case of galactose, identical retention times due to symmetry. We, therefore, developed and validated an easy method for the quantitative distinction between 3-O-methyl- and 4-O-methyl-hexoses and showed its functionality by quantification of 3-O-methyl galactose in a high molecular weight polysaccharide mixture from the charophyte Spirogyra. A systematic search for methylated monosaccharides in different plant lineages may offer new insights in plant cell wall evolution.
Highlights
Methyl decoration of hydroxyl groups of monosaccharides is a rare modification of different carbohydrates, being described from different phyla of organisms, except mammals
Wohlschlager et al [2] proposed an endogenous function in the innate immune system in different vertebrates and invertebrates, while Lechner et al [3] showed a role of transient methylated hexoses in the biosynthesis of sulfated glycoproteins in Halobacterium halobium
(4-OMe-Gal) is present for example in the agar fraction of the red alga Gelidium amansii [4], which represents the first description of this sugar modification in nature, and in a sulfated polysaccharide from the red alga Aeodes ulvoidea [5]
Summary
Methyl decoration of hydroxyl groups of monosaccharides is a rare modification of different carbohydrates, being described from different phyla of organisms, except mammals. 4-O-methyl-galactose (4-OMe-Gal) is present for example in the agar fraction of the red alga Gelidium amansii [4], which represents the first description of this sugar modification in nature, and in a sulfated polysaccharide from the red alga Aeodes ulvoidea [5]. 3-OMe-Gal has been reported previously in a neutral polysaccharide of the green alga Chlorella vulgaris [7,8], it has not been found in any other genera of the Chlorophyta. In land plants, it was detected in sweet chestnut leaves [9], in pectic. The upper two panels show 3-OMe-galactose, while the lower two show 4-OMegalactose
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