Abstract
Rhamnogalacturonan II (RG-II) is a type of block copolymer of complex pectins that represents a quantitatively minor component of the primary cell walls of land (vascular) plants. The structural composition of RG-II is almost totally sequenced and appears to be remarkably conserved in all tracheophytes so far examined. The backbone of RG-II, released from complex (cell wall) pectins by endo-polygalacturonase (Endo-PG) treatment, has been found to contain up to 15 (1→4)-linked-α-D-GalpA units, some of which carry four well-defined side chains, often referred to as A-, B-, C-, and D-side chains. Nevertheless, the relative locations on the backbone of these four branches, especially the A chain, remain to be ascertained. A combination of different data suggests that neither the terminal nonreducing GalA nor the contiguous GalA unit is likely to be the branching point of the A chain, but probably the ninth GalA residue from the reducing end, assuming a minimum backbone length of 11 (1→4)-linked-α-d-GalpA. The latest reports on RG-II are here highlighted, with a provided update for the macrostructure and array of functionalities.
Highlights
The primary cell walls (PCWs) of plants encompass two independent and interacting polysaccharide networks, the first of which is a pectin network considered to be a matrix in which the second network is thought to be embedded [1, 2]
The pectin network is generally believed to be formed with three block copolymers, namely, homogalacturonan (HG), rhamnogalacturonan-I (RG-I), and the “substituted galacturonan (SG)” rhamnogalacturonan-II (RG-II) [3, 4], though other pectic polysaccharide types, namely, xylogalacturonan (XGA), apiogalacturonan (ApGA), galacturonogalacturonan (GaGA), galactogalacturonan (GGA), and arabinogalacturonan (ArGA), which are SGs, have been purified from plant cell wall materials [5,6,7,8]
The formation of dRG-II is required for the formation of the pectin network in muro that contributes to the mechanical strength and physical properties of the PCW and is essential to normal plant growth and development
Summary
The primary cell walls (PCWs) of plants encompass two independent and interacting polysaccharide networks, the first of which is a pectin network considered to be a matrix in which the second network (cellulose/hemicelluloses) is thought to be embedded [1, 2]. The pectin network is generally believed to be formed with three block copolymers, namely, homogalacturonan (HG), rhamnogalacturonan-I (RG-I), and the “substituted galacturonan (SG)” rhamnogalacturonan-II (RG-II) [3, 4], though other pectic polysaccharide types, namely, xylogalacturonan (XGA), apiogalacturonan (ApGA), galacturonogalacturonan (GaGA), galactogalacturonan (GGA), and arabinogalacturonan (ArGA), which are SGs, have been purified from plant cell wall materials [5,6,7,8]. The demonstration that RG-II exists in primary walls predominantly as a dimer (dRG-II) that is covalently cross-linked by a borate diester is a major advance in our understanding of the structure and function of this pectic polysaccharide type [9]. This paper aims at highlighting the latest findings on RG-II and updating the structural features and array of (bio)functionalities of this highly complex block copolymer of pectins from the PCWs of land plants
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
