Structural features conserved in subclass of type II arabinogalactan

Area of Science:

• Plant Biology
• Biochemistry
• Glycobiology

Background:

• Arabinogalactan-proteins (AGPs) are key extracellular proteoglycans in plants.
• AGPs regulate cell shape and contribute to plant mechanical properties.
• They consist of a hydroxyproline-rich core and type II arabinogalactan (AG) sugar chains.

Purpose of the Study:

• To investigate the structural similarities of type II AGs in the AGP-subclass from herbaceous plants.
• To compare the structure of type II AGs from vegetables with those from woody plants (gum arabic-subclass).

Main Methods:

• Enzymatic hydrolysis of type II AGs from spinach, broccoli, bok choy, komatsuna, and cucumber.
• Analysis of released galactose and β-1,6-galactooligosaccharides.
• Calculation of the substitution ratio of the β-1,3-galactan backbone.

Main Results:

• The substitution ratio of the β-1,3-galactan backbone in vegetables ranged from 46-58%.
• This ratio is consistently lower than that observed in gum arabic and larch AG.
• While mostly short, some long β-1,6-galactohexaose side chains were detected.

Conclusions:

• A conserved β-1,3;1,6-galactan structure exists in the AGP-subclass from vegetables.
• This structure differentiates the AGP-subclass from the gum arabic-subclass found in woody plants.