Nucleoside diphosphate sugar hydrolase that hydrolyzes GDP-mannose as its preferred substrate, yielding GMP and mannose-1-phosphate. Can also hydrolyze the pyrophosphate bond of other sugar nucleotides such as IDP-ribose, GDP-glucose, and to a lesser extent, ADP-ribose, ADP-glucose and UDP-glucose. Shows no activity toward Nudix substrates FAD, CDP-ethanolamine, CDP-choline, NAD(+), diadenosine pentaphosphate, GTP, UTP, ATP, or CTP. GDP-alpha-D-mannose + H2O = alpha-D-mannose 1-phosphate + GMP + 2 H(+) GDP-alpha-D-glucose + H2O = alpha-D-glucose 1-phosphate + GMP + 2 H(+) kcat is 90.2 sec(-1) with GDP-mannose as substrate (at pH 8.5 and 37 degrees Celsius) (PubMed:21638333). The rate of hydrolysis of GDP-glucose is half the rate of GDP-mannose (PubMed:21638333, PubMed:16766526). Optimum pH is about 8.5. Homodimer. In the dimer, the N-terminal domains are swapped between the two monomers, such that residues of both chains contribute to the active site. Cells lacking this gene show no defect in their capacity of forming biofilms. Belongs to the Nudix hydrolase family. NudK subfamily.