Pectin structure

Abstract

Pectin is a highly complex polysaccharide made of three main domains that are covalently linked one to another, homogalacturonan, rhamnogalacturonan I and rhamnogalacturonan II. The dominant feature of pectin consists of a linear chain of α-(1,4)-linked d-galacturonic acid units known as homogalacturonan domain or pectin smooth region. The second fundamental feature of pectin structure is the recurrent presence of rhamnosyl residues. α-(1,4)-Linked d-galacturonopyranosyl units can be interrupted by the insertion of α-(1,2)-linked l-rhamnopyranosyl units giving a type I rhamnogalacturonan to which arabinose-and galactose-containing side-chains are generally attached. Finally, rhamnogalacturonan II consisting of a highly branched homogalacturonan oligosaccharide, is a minor though crucial element of pectin. Although, as illustrated in this chapter, much is known about the structure of the different pectin domains, understanding the intra-and inter-molecular heterogeneity of pectin macromolecules and the way pectin domains are attached to each other is still challenging.