Metrics of rhamnogalacturonan I with β-(1→4)-linked galactan side chains and structural basis for its self-aggregation.

Within the family of plant cell wall polysaccharides rhamnogalacturonans I are the most diverse and structurally complex members. In present study we characterize the 3-dimensional structures and dynamic features of the constituents of RG-I along MD trajectories. It is demonstrated that extended threefold helical structure of the rhamnogalacturonan linear backbone is the most energetically favorable motif. Branching helps to stabilize a conformer of the backbone twisted along 1→2 glycosidic linkage triggering the orientation of long side chains without altering the extended overall backbone chain conformation. Formation of anti-parallel pairing of the β-galactan side chains allows us to suggest a novel mode of non-covalent cross-linking in pectins. Studied structural elements are organized to report the first attempt to characterize 3D structure of RG-I focusing on the special case of flax tertiary cell wall and elucidate the structural basis underlying the formation of RG-I self-associates and functional role of RG-I in planta.