HAO1 Human
Description
Structure and Function
HAO1 is a 45 kDa flavin mononucleotide (FMN)-dependent enzyme encoded by the HAO1 gene on chromosome 20. It exists as a homotetramer, with each subunit containing an α/β TIM barrel fold and a flexible "gating loop" (aa 169–212) that regulates substrate access . Key structural features include:
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FMN Binding Site: The FMN cofactor is stabilized by polar interactions in a hydrophobic pocket .
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Substrate Specificity: Preferentially oxidizes glycolate (C2) but also acts on 2-hydroxy fatty acids (e.g., 2-hydroxypalmitate) .
Table 1: Substrate Activity of HAO1
| Substrate | Activity Level | Key Role |
|---|---|---|
| Glycolate | High | Primary substrate |
| 2-Hydroxy fatty acids | Moderate | Secondary metabolism |
| D-DOPA | Low | Dopamine synthesis |
Metabolic and Clinical Significance
HAO1 oxidizes glycolate to glyoxylate, which is further converted to oxalate. Dysregulation of this pathway can lead to oxalate accumulation, causing kidney stones in PH1 .
Role in Primary Hyperoxaluria Type 1 (PH1)
PH1 arises from mutations in AGXT (alanine-glyoxylate aminotransferase), leading to glycolate buildup. HAO1 inhibition reduces glycolate oxidation to oxalate, offering a therapeutic strategy .
Natural HAO1 Knockout Case Study
A healthy woman with a homozygous HAO1 frameshift mutation (p.Leu333SerfsTer4) exhibited:
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Elevated Glycolate:
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Metabolomics: 18 metabolites >5 SD above controls, including unconjugated bile acids and fatty acid derivatives .
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No Clinical Phenotype: Lifelong HAO1 deficiency showed no organ damage or toxicity, supporting the safety of HAO1 inhibition .
Table 2: Key Findings from HAO1 Knockout Study
| Parameter | Value (Knockout) | Controls (n=25) |
|---|---|---|
| Plasma Glycolate | 171 nmol/mL | 14 nmol/mL (mean +2SD) |
| Urinary Glycolate | 6× upper limit | Normal |
| Unconjugated Bile Acids | Elevated | Normal |
Therapeutic Implications
HAO1 inhibition is a validated approach for PH1:
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Lumasiran: An RNAi therapeutic targeting HAO1, approved for PH1 treatment, reduces plasma glycolate by ~75% .
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Mechanism: Suppresses glycolate oxidation, shifting metabolism to soluble glycolate excretion .
Challenges:
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Long-Term Safety: Requires lifelong therapy, necessitating monitoring for off-target effects .
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Structural Insights: Fragment-based screening identified active-site and interface-binding inhibitors, guiding drug design .
Research Challenges and Future Directions
Product Specs
Product Science Overview
HAO1 catalyzes the oxidation of glycolate to glyoxylate and glyoxylate to oxalate, with the reduction of oxygen to hydrogen peroxide . This enzyme exhibits 2-hydroxyacid oxidase activity and is most active on two-carbon substrates such as glycolate . It can also act on 2-hydroxy fatty acids, with higher activity towards 2-hydroxy palmitate and 2-hydroxy octanoate .
In the context of peroxisomal glyoxylate metabolism, HAO1 is the enzyme upstream of alanine-glyoxylate aminotransferase (AGXT). Mutations in AGXT cause Primary Hyperoxaluria type 1 (PH1), an autosomal recessive disorder characterized by the deposition of insoluble calcium oxalate stones . These stones primarily accumulate in the kidneys, leading to end-stage renal disease, but can also deposit in other tissues such as the heart, nerves, bones, eyes, and bone marrow .
Recombinant HAO1 is produced using expression hosts such as E. coli. The recombinant protein is typically tagged for purification and analysis purposes. For example, a His-tagged recombinant human HAO1 protein has a calculated molecular weight of approximately 58.6 kDa and an observed molecular weight of 56 kDa . The protein is purified to a high degree, with a purity of over 95% as determined by reducing SDS-PAGE .
