It could participate in the regulation of cell wall biosynthesis by influencing the concentration of GDP-mannose or GDP-glucose in the cell. May be involved in the degradation of GDP-mannose and GDP-glucose, diverting the GDP to the synthesis of GDP-fucose as required (By similarity). GDP-alpha-D-mannose + H2O = D-mannose + GDP + H(+) Binds 1 Mg(2+) ion per subunit. Bacterial outer membrane biogenesis; LPS O-antigen biosynthesis. Homodimer. Belongs to the Nudix hydrolase family.