This is the highly conserved galactokinase signature sequence which appears to be present in all galactokinases irrespective of how many other ATP binding sites, etc that they carry [1]. The function of this domain appears to be to bind galactose [2], and the domain is normally at the N-terminus of the enzymes, EC:2.7.1.6 [3]. This domain is associated with the families GHMP_kinases_C, Pfam:PF08544 and GHMP_kinases_N, Pfam:PF00288.

1: The trappin gene family: proteins defined by an N-terminal transglutaminase substrate domain and a C-terminal four-disulphide core. Schalkwijk J, Wiedow O, Hirose S; Biochem J. 1999;340:569-577. PMID:10359639

2: Molecular structure of galactokinase. Thoden JB, Holden HM; J Biol Chem. 2003;278:33305-33311. PMID:12796487

3: Galactokinase: structure, function and role in type II galactosemia. Holden HM, Thoden JB, Timson DJ, Reece RJ; Cell Mol Life Sci. 2004;61:2471-2484. PMID:15526155