Figure 1.

Rhamnogalacturonan II. (A) The glycosyl sequence of RG-II. The nominal mass for the RG-II monomer is 4,612, assuming a backbone of 7 GalA residues and fully decorated side chains. (B) Cartoon showing the cross-linking of two RG-II molecules. (C) The borate diester cross-link. When two apiosyl residues are linked by a borate diester, the boron atom is chiral, and two diastereoisomers (bis[3-C-(hydroxymethyl)-β-l threo-furanoside]-(R)-2,3:2′,3′ borate) and (bis[3-C-(hydroxymethyl)-β-l- threo-furanoside]-(S)-2,3:2′,3′ borate may form (O’Neill et al., 2004). It is not known if one or both diastereoisomers are formed when RG-II is cross-linked in the cell wall.