Human Fructosamine-3-Kinase

Abstract

Nonenzymatic glycation appears to be an important factor in the pathogenesis of diabetic complications. Key early intermediates in this process are fructosamines, such as protein-bound fructoselysines. In this report, we describe the purification and characterization of a mammalian fructosamine-3-kinase (FN3K), which phosphorylates fructoselysine (FL) residues on glycated proteins, to FL-3-phosphate (FL3P). This phosphorylation destablilizes the FL adduct and leads to its spontaneous decomposition, thereby reversing the nonenzymatic glycation process at an early stage. FN3K was purified to homogeneity from human erythrocytes and sequenced by means of electrospray tandem mass spectrometry. The protein thus identified is a 35-kDa monomer that appears to be expressed in all mammalian tissues. It has no significant homology to other known proteins and appears to be encoded by genomic sequences located on human chromosomes 1 and 17. The lability of FL3P, the high affinity of FN3K for FL, and the wide distribution of FN3K suggest that the function of this enzyme is deglycation of nonenzymatically glycated proteins. Because the condensation of glucose and lysine residues is an ubiquitous and unavoidable process in homeothermic organisms, a deglycation system mediated by FN3K may be an important factor in protecting cells from the deleterious effects of nonenzymatic glycation. Our sequence data of FN3K are in excellent agreement with a recent report on this enzyme by Delpierre et al.

Degradation products of proteins damaged by glycation, oxidation and nitration in clinical type 1 diabetes

“…Estimates reported here are similar to those reported previously [25]. The increased FL urinary excretion in diabetes may underestimate increased formation in diabetes, as FL urinary excretion is metabolised efficiently by fructosamine-3-phosphokinase [26]. FL residues in haemoglobin correlated positively with measures of glycaemic control, HbA 1 c and 24hG, whereas FL residues in plasma protein correlated negatively with CEL and 3DG-H residues.…”

“…The concentrations of MG-H1 and 3DG-H in haemoglobin were approximately ten-fold higher than the concentrations of CML and CEL residues, and 100-and 500-fold higher than the concentrations of MOLD and pentosidine residues respectively. Formation of 3DG-H in RBCs may be linked to the formation of 3-DG by the deglycating action of fructosamine-3-phosphokinase on HbA 1 c [26,33]. Application of matrix-assisted laser desorption ionisation (MALDI) mass spectrometry gave evidence of multiple types of modified haemoglobin in diabetes by molecular mass measurement of haemoglobin subunits [34], consistent with the findings of this study.…”

“…The predicted contributions of plasma protein and haemoglobin degradation to the excretion of protein glycation, oxidation and nitration free adducts revealed predicted excess production of MetSO and FL free adducts, consistent with the efficient metabolism of MetSO by MetSO reductase [48] and repair of FL residues and free adducts by fructosamine-3-phosphokinase [26,33]. NFK and 3-NT are also metabolised to kynurenine [49] and 3-nitro-4-hydroxyphenylacetic acid [50] respectively.…”

Red cell life span heterogeneity in hematologically normal people is sufficient to alter HbA1c

“…1,2 If both glycation and deglycation are occurring simultaneously, there is no evidence of a complex time course from mean cell age until cells are removed from the circulation. A deglycating enzyme 43 has recently been identified that acts at lysine, but none has been reported that acts at the N-terminal glycated amino group. 44 The strong correlation of glycation rate with whole blood HbA1c in the DM and NDM subjects ( Figure 5) provides evidence that the whole blood determination depends on the integration of glycation rate throughout the red cell life span.…”

Reduced fructosamine-3-kinase activity and its mRNA in human distal colorectal carcinoma

“…The non-enzymatic reaction of protein amino groups with glucose and other reducing sugars has long been considered irreversible [8,25]. However, recent evidence indicates that fructosamines can be repaired by Fructosamine-3-Kinase (FN3K), which phosphorilates fructoselysine (FL) residues on glycated proteins, resulting in the production of protein-bound FL-3-phosphate (FL3P) [16].…”