Guanylate kinase catalyzes the ATP-dependent phosphorylation of GMP into GDP.

In prokaryotes (such as Escherichia coli), lower eukaryotes (such as yeast) and in vertebrates, GK is a highly conserved monomeric protein of about 200 amino acids.

GK has been shown to be structurally similar to protein A57R (or SalG2R) from various strains of Vaccinia virus.

[2][3][4] Systems biology analyses carried out by the team of Andreas Dräger also identified a pivotal role of this enzyme in the replication of SARS-CoV-2 within the human airways.

[5][6][7] The systematic name of this enzyme class is ATP:(d)GMP phosphotransferase.