This entry corresponds to a group of metazoan glycerol kinases (GKs), coded by X chromosome-linked GK genes, and glycerol kinase (GK)-like proteins, coded by autosomal testis-specific GK-like genes GK2, GK3 and Gykl1 (in mouse). These are thought to have arise by the transposition of Gk located on the Xchromosome []. Sequence comparison shows that metazoan GKs and GK-like proteins in this family are closely related to the bacterial GKs, which catalyze the Mg-ATP dependent phosphorylation of glycerol to yield glycerol 3-phosphate (G3P). The metazoan GKs do have GK enzymatic activity. However, the GK-like metazoan proteins do not exhibit GK activity and their biological functions are not yet clear []. Some of them lack important functional residues involved in the binding of ADP and Mg2+, which may result in the loss of GK catalytic function. Others that have conserved catalytic residues have lost their GK activity as well; the reason remains unclear. It has been suggested the conserved catalytic residues might facilitate them performing a distinct function. GK2 seem to be necessary for the formation of the mitochondrial sheath during spermatogenesis [, ].GKs belong to the FGGY family of carbohydrate kinases, the monomers of which contain two large domains, which are separated by a deep cleft that forms the active site [].
