Ribokinase (RK) belongs to the phosphofructokinase B (PfkB) family of sugar kinases.

[1][2][3] The members of the PfkB/RK family are identified by the presence of three conserved sequence motifs and the enzymatic activity of this family of protein generally shows a dependence on the presence of pentavalent ions.

[1][2][4] The conserved NXXE motif, which is a distinctive property of the PfkB family of proteins, is involved in pentavalent ion dependency.

The structures of RK and several other PfK family of proteins have been determined from a number of organisms.

[1] As of late 2007, 7 structures have been solved for this class of enzymes, with PDB accession codes 1GQT​, 1RK2​, 1RKA​, 1RKD​, 1RKS​, 1VM7​, and 2FV7​.