Identification and characterisation of a new human glucose‐6‐phosphatase isoform

Abstract

The liver endoplasmic reticulum glucose-6-phosphatase catalytic subunit (G6PC1) catalyses glucose 6-phosphate hydrolysis during gluconeogenesis and glycogenolysis. The highest glucose-6-phosphatase activities are found in the liver and the kidney; there have been many reports of glucose 6-phosphate hydrolysis in other tissues. We cloned a new G6Pase isoform (G6PC3) from human brain encoded by a six-exon gene (chromosome 17q21). G6PC3 protein was able to hydrolyse glucose 6-phosphate in transfected Chinese hamster ovary cells. The optimal pH for glucose 6-phosphate hydrolysis was lower and the K m higher relative to G6PC1. G6PC3 preferentially hydrolyzed other substrates including pNPP and 2-deoxy-glucose-6-phosphate compared to the liver enzyme.

Long-term correction of murine glycogen storage disease type Ia by recombinant adeno-associated virus-1-mediated gene transfer

“…We, and others, have recently reported the characterization of a ubiquitously expressed G6P hydrolase, G6Pase-b. 31,32 G6Pase-b appears very similar to G6Pase-a in that it shares structural and kinetic similarities to G6Pase-a and couples with G6PT to form an active G6Pase-b complex. 31 However, the overall activity of G6Pase-b is only B12% that of G6Pase-a.…”

In islet-specific glucose-6-phosphatase-related protein, the beta cell antigenic sequence that is targeted in diabetes is not responsible for the loss of phosphohydrolase activity

“…Only these tissues were known to express G6Pase-α [5,8], which is required to convert G6P, generated by gluconeogenesis and glycogenolysis, into glucose for release to the blood. Recently, however, two additional members of the G6Pase family, G6Pase-β [9][10][11][12] and IGRP [13][14][15][16] were identified. IGRP, which bears the closest protein sequence to G6Pase-α, is expressed solely in the pancreatic beta cells [13,14], while G6Pase-β, a more distant relative, is expressed ubiquitously [9].…”

“…IGRP, which bears the closest protein sequence to G6Pase-α, is expressed solely in the pancreatic beta cells [13,14], while G6Pase-β, a more distant relative, is expressed ubiquitously [9]. G6Pase-β has an activity very similar to G6Pase-α, although its specific activity is only ∼12% that of G6Pase-α [10,11]. Surprisingly, IGRP, which is more closely relat- In vitro synthesis of G6Pase-α directed by FLAG-tagged wildtype or mutant G6Pase-α construct in a pGEM-11Zf vector was performed using the TnT coupled reticulocyte lysate system.…”

“…G6Pase-α (G6PC) [6,7] is expressed primarily in the liver, kidney and intestine [5,8]. G6Pase-β (G6PC3 or UGRP) [9][10][11][12] is expressed ubiquitously, while the islet-specific G6Pase-related protein (G6PC2 or IGRP) [13][14][15][16] is restricted to expression in the pancreas. All three proteins are similarly orientated within the membrane of the endoplasmic reticulum and contain nine transmembrane domains [12,16,17].…”

“…Characterisation of the naturally occurring inactivating mutations of G6Pase-α, combined with site directed mutagenesis, has identified 43 key residues required for hydrolytic activity [24]. G6Pase-β, the second most active member of the family, which shares an overall 36% sequence identity [9][10][11] and retains 35 of the 43 critical residues identified in G6Pase-α [10], possesses ∼12% of the G6P hydrolytic activity of G6Pase-α [10]. The third and most closely related family member to G6Pase-α is IGRP.…”