X-ray fiber diffraction studies of a variant of xanthan gum in which the sidechain terminal mannose unit is absent

Abstract

A variant of xanthan gum produced by a genetically engineered mutant of Xanthomonas campestris, in which the sidechain terminal mannose unit is absent, has been trapped in an ordered conformation in oriented fibers. X-ray diffraction patterns from these fibers show that the variant polymer has a molecular repeat of 47·5 Å and five-fold helix symmetry, almost identical to that of xanthan. They also suggest that the effective molecular diameter is approximately 3 Å less than that of xanthan. These results indicate that the conformation of the variant polymer is similar to that of xanthan, and show that removal of the sidechain terminal mannose unit does not critically affect the stability of the xanthan ordered structure.