InterPro domain: IPR016477

Ketosamines derive from a non-enzymatic reaction between a sugar and a protein [ 1 ]. Ketosamine-3-kinases (KT3K), of which fructosamine-3-kinase (FN3K) is the best-known example, catalyse the phosphorylation of the ketosamine moiety of glycated proteins. The instability of a phosphorylated ketosamine leads to its degradation, and KT3K is thus thought to be involved in protein repair [ 2 ].

The function of the prokaryotic members of this group has not been established. However, several lines of evidence indicate that they may function as fructosamine-3-kinases (FN3K). First, they are similar to characterised FN3K from mouse and human. Second, the Escherichia coli members are found in close proximity on the genome to fructose-6-phosphate kinase (PfkB). Last, FN3K activity has been found in a Anacystis montana (Gloeocapsa montana Kutzing 1843) [ 3 ], indicating such activity-directly demonstrated in eukaryotes-is nonetheless not confined to eukaryotes.

This family includes eukaryotic fructosamine-3-kinase enzymes [ 4 ] which may initiate a process leading to the deglycation of fructoselysine and of glycated proteins and in the phosphorylation of 1-deoxy-1-morpholinofructose, fructoselysine, fructoseglycine, fructose and glycated lysozyme. The family also includes bacterial members that have not been characterised but probably have a similar or identical function.

1. Fructosamine: structure, analysis, and clinical usefulness. Clin. Chem. 33, 2153-63
2. A mammalian protein homologous to fructosamine-3-kinase is a ketosamine-3-kinase acting on psicosamines and ribulosamines but not on fructosamines. Diabetes 52, 2888-95
3. Distribution of adenosine 5'-triphosphate (ATP)-dependent hexose kinases in microorganisms. BioSystems 10, 265-82
4. Identification, cloning, and heterologous expression of a mammalian fructosamine-3-kinase. Diabetes 49, 1627-34