Rhamnogalacturonan backbone

Arabinofuranosides were removed from PVa, which resulted in an increase in the activity this was in contrast to the findings of Kiyohara et al. [35] who foimd no change in activity after removal of similar units from A. acutiloba pectin. For this polymer it was suggested that the minimum requirement for complement activation via the classical pathway was j6-l,6-linked galactan attached to the rhamnogalacturonan backbone, which also appears to be an important part of the backbone for PVa. 

The length of the arabinan side chains present in subunit II may vary between 30 and 50 arabinose residues and several of these chains might be connected to the rhamnogalacturonan backbone which consists of only 8-10 sugar residues (ratio of rhamnose to galacturonic acid is 0.2 to 0.4). The arabinans might be connected directly to a rhamnose residue in the backbone or via one or more galactose residues [41]. 

We believe that single molecule imaging can contribute to a more thorough understanding of the role of pectin in the cell wall. Our future efforts will be focused on pectin gels formed in the presence of calcium. Eventually, it should be possible to visualize side chains on pectin and determine how rhamnose residues in the rhamnogalacturonan backbone of tobacco pectin disrupt the formation of helical regions. 

Figure 5. Model of the pectins of types A-E. Horizontal lines rhamnogalacturonan backbone of the pectin molecule. Black areas blocks of neutral sugar side chains. (Reproduced with permission from reference 2. Copyright 1982 Carbohydrate Polymer).

These data confirm what is known already for certain other pectins, e.g. from apples (20) and cherry fruits (17), that the neutral sugar side chains attached to the rhamnogalacturonan backbone occur in blocks, the so-called "hairy fragments", leaving large parts of the main chain unsubstituted ("smooth fragments"). 

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