The research report should be a detailed narrative explaining the function, biological processes, and localization of the gene product. Citations should be given for all claims.
You should prioritize authoritative reviews and primary scientific literature when conducting research. You can supplement
this with annotations you find in gene/protein databases, but these can be outdated or inaccurate.
We are specifically interested in the primary function of the gene - for enzymes, what reaction is catalyzed, and what is the substrate specificity? For transporters, what is the substrate? For structural proteins or adapters, what is the broader structural role? For signaling molecules, what is the role in the pathway.
We are interested in where in or outside the cell the gene product carries out its function.
We are also interested in the signaling or biochemical pathways in which the gene functions. We are less interested in broad pleiotropic effects, except where these elucidate the precise role.
Include evidence where possible. We are interested in both experimental evidence as well as inference from structure, evolution, or bioinformatic analysis. Precise studies should be prioritized over high-throughput, where available.
G6PC1 is the correct human protein for UniProt P35575: glucose-6-phosphatase catalytic subunit 1, historically called G6PC or glucose-6-phosphatase-α. The reviewed protein is an endoplasmic-reticulum (ER) membrane enzyme of the PAP2-related phosphatase family, consistent with the supplied domain annotations. It is not the pancreatic paralog G6PC2 or the more widely expressed G6PC3. Importantly, G6PT is also the established name of a different protein, the G6P transporter SLC37A4; despite its appearance among the supplied synonyms, G6PC1 should not be assigned a transport function. A 2025 human structural study explicitly identifies its G6PC1 construct as UniProt P35575. (lizak2019glucosetransportand pages 3-5, hawes2024identificationofstructural pages 1-2, chen2025theinducedfitand pages 1-2)
The table summarizes the functional assignment and the distinction between experiments on the human enzyme and its mouse ortholog.
| Aspect | Human G6PC1/P35575 findings | Evidence and interpretation |
|---|---|---|
| Identity and nomenclature | G6PC1, formerly G6PC, encodes glucose-6-phosphatase catalytic subunit 1, also called G6Pase-α. It is distinct from G6PC2, G6PC3, and the separate transporter G6PT/SLC37A4. | G6PC1 is the membrane-embedded catalytic enzyme, whereas SLC37A4 transports G6P. Accordingly, G6PC1 itself should not be annotated as G6PT. (lizak2019glucosetransportand pages 3-5, hawes2024identificationofstructural pages 1-2) |
| Primary reaction | D-glucose 6-phosphate + H₂O → D-glucose + inorganic phosphate; EC 3.1.3.9. | Human structural evidence places G6P in the active-site cavity and identifies His176 as the catalytic nucleophile, with His119 assisting phosphoester cleavage. (chen2025theinducedfitand pages 2-3, chen2025theinducedfitand pages 8-9) |
| Phosphosugar specificity | G6P is the physiological substrate. Purified mouse G6PC1, an 89%-identical ortholog rather than human P35575, hydrolyzed G6P and M6P at similar rates. F6P activity was approximately 26–30% of G6P activity at 1.5 mM, and catalytic efficiency for G6P was more than tenfold higher than for F6P. | These results demonstrate intrinsic phosphosugar promiscuity but do not establish M6P or F6P as major human physiological substrates. Mouse WT G6PC1 in LMNG had a G6P Kₘ of 0.431 ± 0.08 mM, kcat of 41 s⁻¹, and kcat/Kₘ of 9.6 × 10⁴ M⁻¹ s⁻¹; purified human G6PC1 had an apparent G6P Kₘ of approximately 2 mM. (chen2025theinducedfitand pages 2-3, claxton2022biophysicalandfunctional pages 1-2, claxton2022biophysicalandfunctional pages 4-5, claxton2022biophysicalandfunctional pages 5-6) |
| Family and localization | G6PC1 is a PAP2-family, multispanning integral membrane glycoprotein of the endoplasmic-reticulum membrane. It has nine transmembrane helices, an N-luminal and C-cytosolic orientation, and a positively charged catalytic pocket opening toward the ER lumen. | Cryo-EM and purified-protein evidence support a luminal active site rather than a cytosolic catalytic site. (chen2025theinducedfitand pages 2-3, chen2025theinducedfitand pages 1-2, claxton2022biophysicalandfunctional pages 1-2) |
| Coupled ER system | SLC37A4/G6PT imports cytosolic G6P into the ER. G6PC1 hydrolyzes it within the lumen, after which glucose and phosphate leave the ER. | Transport and catalysis are performed by different proteins. Transport-dependent substrate access means that intrinsic enzyme activity alone does not determine physiological substrate use. (lizak2019glucosetransportand pages 3-5, hutton2009glucose6phosphatasecatalyticsubunit pages 1-1) |
| Physiological pathway | G6PC1 performs the terminal common step of gluconeogenesis and glycogenolysis, enabling fasting glucose output principally from liver and kidney, with expression also reported in intestine. | Its position at the shared endpoint of these pathways makes G6PC1 a gatekeeper of interprandial blood-glucose homeostasis. (hawes2024identificationofstructural pages 1-2, claxton2022biophysicalandfunctional pages 1-2) |
| Loss of function | Biallelic pathogenic G6PC1 variants cause glycogen storage disease type Ia. Failed G6P hydrolysis produces fasting hypoglycemia, glycogen and lipid accumulation, hepatomegaly, nephromegaly, hyperlipidemia, hyperuricemia, and lactic acidemia. | In a 2024 humanized G6PC1-p.R83C mouse model, hepatic activity was 2.2 ± 0.3 units, compared with 330.4 ± 36.3 units in wild-type animals, and only 39% of untreated animals survived to three weeks. (arnaoutova2024baseeditingcorrectsmetabolic pages 1-2) |
Table: Compact annotation of human G6PC1/P35575 covering identity, catalytic function, specificity, ER topology, pathway role, and loss-of-function disease. It distinguishes the catalytic enzyme from SLC37A4/G6PT and explicitly labels mouse-derived kinetic evidence.
G6PC1 catalyzes the hydrolytic reaction D-glucose 6-phosphate + H₂O → D-glucose + inorganic phosphate (EC 3.1.3.9). This is the final common biochemical step that allows glucose derived from either glycogenolysis or gluconeogenesis to be released for maintenance of blood glucose during fasting. The enzyme removes phosphate; it does not transport G6P across the ER membrane. (hutton2009glucose6phosphatasecatalyticsubunit pages 1-1, claxton2022biophysicalandfunctional pages 1-2)
G6P is the established physiological substrate, but intrinsic phosphatase activity is not absolutely restricted to it. In a direct study of purified mouse G6PC1, G6P and mannose 6-phosphate (M6P) were hydrolyzed at similar rates, whereas fructose 6-phosphate (F6P) produced approximately 26–30% of the G6P-associated phosphate-release rate under the comparison conditions; catalytic efficiency for G6P was more than tenfold that for F6P. For purified mouse enzyme in LMNG detergent, measured G6P Kₘ was 0.431 ± 0.08 mM and turnover number 41 s⁻¹. These are mouse-ortholog, detergent-solubilized measurements, not kinetic constants established for human tissues. A subsequent human purified-protein study reported an approximately 2 mM G6P Kₘ and directly visualized bound G6P and F6P. Moreover, M6P is not efficiently delivered by the relevant ER G6P transporter; activity on an accessible substrate in vitro does not make it an important substrate of the intact physiological system. (chen2025theinducedfitand pages 2-3, claxton2022biophysicalandfunctional pages 4-5, claxton2022biophysicalandfunctional pages 5-6, claxton2022biophysicalandfunctional media 439614ff)
Structural work published in July 2025 provides unusually direct mechanistic evidence for this human protein. Cryo-electron microscopy captured apo, substrate-bound, and phosphate-bound conformations of G6PC1. Its conserved PAP2-like catalytic motifs line a positively charged substrate cavity: Arg83 and Arg170 interact with the substrate phosphate, His176 is proposed to attack phosphorus as the catalytic nucleophile, and His119 assists cleavage of the glucose–phosphate bond. Substrate binding reorganizes the cavity in an induced-fit mechanism. These atomic assignments refine, rather than replace, the older physiological evidence for G6P hydrolysis. (chen2025theinducedfitand pages 2-3, chen2025theinducedfitand pages 1-2, chen2025theinducedfitand pages 8-9)
G6PC1 is a multispanning integral ER-membrane protein, not a secreted enzyme or plasma-membrane glucose exporter. The human structure supports nine membrane-spanning helices and a catalytic cavity accessible on the ER-luminal side; its N terminus is luminal and C terminus cytosolic. The ER system works in sequence: SLC37A4/G6PT moves cytosolic G6P into the lumen; G6PC1 hydrolyzes it there; glucose and phosphate subsequently leave the ER. Thus both catalytic competence and substrate access determine net glucose production. The precise assignment of every product-export pathway is less secure than the experimentally established distinction between G6PC1 catalysis and SLC37A4-mediated G6P entry. (lizak2019glucosetransportand pages 3-5, chen2025theinducedfitand pages 2-3, hutton2009glucose6phosphatasecatalyticsubunit pages 1-1, claxton2022biophysicalandfunctional pages 1-2)
G6PC1 expression is particularly important in liver and kidney, with expression also reported in intestine. Its immediate pathway role is terminal glucose release from G6P, not glycogen cleavage or the upstream synthesis of G6P. The enzyme therefore couples the two upstream sources of G6P—glycogen breakdown and gluconeogenic carbon—to systemic fasting glucose supply. Insulin represses, whereas glucagon promotes, hepatic G6PC1 expression; those regulatory effects alter the capacity for this specific terminal reaction and should not be confused with G6PC1 acting as a hormone receptor or signaling protein. (hawes2024identificationofstructural pages 1-2, claxton2022biophysicalandfunctional pages 1-2, arnaoutova2024baseeditingcorrectsmetabolic pages 1-2)
Biallelic loss-of-function G6PC1 variants cause glycogen storage disease type Ia (GSD-Ia), distinct from GSD-Ib due to deficiency of the transporter SLC37A4. The failure to convert luminal G6P into glucose explains fasting hypoglycemia and, through accumulation and diversion of G6P, the characteristic hepatic and renal glycogen accumulation and metabolic abnormalities, including hyperlipidemia, hyperuricemia, and lactic acidemia. In a 2024 humanized mouse carrying pathogenic G6PC1 p.R83C, hepatic G6Pase activity measured 2.2 ± 0.3 versus 330.4 ± 36.3 activity units in wild-type mice; 39% of untreated mutants survived to three weeks. These model results provide a strong loss-of-function test but are not estimates of human survival or human enzyme activity. (lizak2019glucosetransportand pages 3-5, arnaoutova2024baseeditingcorrectsmetabolic pages 1-2)
A November 2024 primary study tested BEAM-301, an intravenously delivered lipid-nanoparticle adenine base editor designed to correct the G6PC1 c.247C>T/p.R83C allele. In humanized mice, correction reached approximately 60% of liver alleles in some animals; the authors reported therapeutic improvement at approximately 10% correction, restored fasting tolerance, and survival through 53 weeks. Liver rescue did not correct the renal enzyme deficiency, and potentially deleterious bystander editing was examined. All efficacy percentages and survival observations here are preclinical, not patient outcomes. The variant-specificity of this editing strategy also limits direct generalization to other G6PC1 genotypes. (arnaoutova2024baseeditingcorrectsmetabolic pages 1-2, arnaoutova2024baseeditingcorrectsmetabolic pages 2-3, arnaoutova2024baseeditingcorrectsmetabolic pages 6-9)
As a real-world translational application, NCT06735755 evaluates BEAM-301 in adults carrying p.R83C. The registry listed this phase 1/2 study as recruiting, with 36 estimated participants; its posted outcomes concern safety, fasting-challenge tolerance, starch supplementation, and metabolic markers, not demonstrated clinical efficacy. Separately, NCT05139316, the phase 3 study of AAV8-mediated G6PC replacement DTX401/pariglasgene brecaparvovec, was listed as completed with 49 actual participants in a registry update posted 25 March 2026. Its prespecified primary endpoint is change in daily cornstarch consumption at week 48; the retrieved registry material did not establish a numerical efficacy result. In its 2024 assessment, Koeberl and colleagues regarded GSD-Ia gene therapy as promising while emphasizing vector immunity, toxicity, and durability as unresolved implementation issues. (NCT06735755 chunk 1, NCT05139316 chunk 1, koeberl2024genetherapyfor pages 13-14)
References
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(arnaoutova2024baseeditingcorrectsmetabolic pages 6-9): Irina Arnaoutova, Yvonne Aratyn-Schaus, Lisa Zhang, Michael S. Packer, Hung-Dar Chen, Cheol Lee, Sudeep Gautam, Francine M. Gregoire, Dominique Leboeuf, Steven Boule, Thomas P. Fernandez, Victoria Huang, Lo-I Cheng, Genesis Lung, Brianna Bannister, Jeremy Decker, Thomas Leete, Lan S. Shuang, Caroline Bock, Prachi Kothiyal, Phil Grayson, Ka W. Mok, Jeffrey J. Quinn, Lauren Young, Luis Barrera, Giuseppe Ciaramella, Brian C. Mansfield, and Janice Y. Chou. Base-editing corrects metabolic abnormalities in a humanized mouse model for glycogen storage disease type-ia. Nature Communications, Nov 2024. URL: https://doi.org/10.1038/s41467-024-54108-1, doi:10.1038/s41467-024-54108-1. This article has 20 citations and is from a highest quality peer-reviewed journal.
(NCT06735755 chunk 1): A Phase 1/2, Dose-Exploration Study to Evaluate the Safety and Efficacy of BEAM-301 in Patients With Glycogen Storage Disease Type Ia (GSDIa). Beam Therapeutics Inc.. 2024. ClinicalTrials.gov Identifier: NCT06735755
(NCT05139316 chunk 1): A Study of Adeno-Associated Virus Serotype 8-Mediated Gene Transfer of Glucose-6-Phosphatase in Patients With Glycogen Storage Disease Type Ia (GSDIa). Ultragenyx Pharmaceutical Inc. 2021. ClinicalTrials.gov Identifier: NCT05139316
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