Spatial structures of rhamnogalacturonan I in gel and colloidal solution identified by 1D and 2D-FTIR spectroscopy

Rhamnogalacturonan I (RG-I), a polysaccharide found in different types of plant cell walls, fulfills specific functions, the structural basis of which remains unclear. Generalized 2D correlation FTIR spectroscopy with dehydration was employed to reveal the structure and interactions in flax RG-I solution and microwave treated gel. Varying water content allowed emphasizing a role of solvent in maintaining different structures. In the gel, 2D correlation maps prove the existence of a conformationally uniform highly hydrated structure. Such a structure is supposed to correspond to non-associated galactan helices stabilized by rare junctions. In colloidal solution the side chains of RG-I associate heterogeneously due to constrains imposed by stiff backbone. Galactan-enriched fraction of RG-I with enzymatically cleaved backbone revealed the tendency of galactan chains to strongly associate in solution. The obtained results shed light on the possible role of backbone and side chains in RG-I spatial organization and confirm the sensitivity and potential of 2D correlation FTIR spectroscopy to probe local ordered structures in non-crystalline polysaccharides.