Selective removal of α- d-galactose side chains from Rhizobium capsular polysaccharide by guar α- d-galactosidase: effect on conformational stability and gelation

Abstract

α- d-Galactosidase, isolated from germinating seeds of guar, removed up to 48% of the (1 → 2)-linked α- d-galactose side chains of Rhizobium capsular polysaccharide (CPS), with no loss of the disaccharide side chains (1 → 6)-linked to the same backbone residues in the hexasaccharide repeating units. Results from differential scanning calorimetry (DSC) and measurements of gel rigidity ( G′) indicate that removal of α- d-galactose side chains facilitates adoption of the “pseudo double-helical” structure proposed from X-ray fibre diffraction analysis (increase in T m and reduction in DSC peak width for conformational ordering on cooling), but progressively eliminates the helix-helix aggregation necessary for gel formation (reduction in thermal hysteresis and in G′).