Nonprocessive beta-mannosyltransferase that catalyzes the transfer of a mannose residue from GDP-mannose to glucuronic acid-beta-1,2-mannose-alpha-1,3-glucose-beta-1,4-glucose-PP-polyisoprenyl to form the lipid-linked pentasaccharide repeating unit of xanthan, Man-GlcA-Man-Glc(2)-PP-Pol. Is involved in the biosynthesis of the exopolysaccharide xanthan (By similarity). beta-D-GlcA-(1->2)-alpha-D-Man-(1->3)-beta-D-Glc-(1->4)-alpha-D-Glc-di-trans,octa-cis-undecaprenyl diphosphate + GDP-alpha-D-mannose = beta-D-Man-(1->4)-beta-D-GlcA-(1->2)-alpha-D-Man-(1->3)-beta-D-Glc-(1->4)-alpha-D-Glc-di-trans,octa-cis-undecaprenyl diphosphate + GDP + H(+) Glycan biosynthesis; xanthan biosynthesis. Belongs to the glycosyltransferase 94 family.