AMPD2 (Adenosine Monophosphate Deaminase 2) encodes a critical enzyme in purine nucleotide metabolism that catalyzes the deamination of adenosine monophosphate (AMP) to inosine monophosphate (IMP), a key step in the adenine nucleotide catabolic pathway[1][2]. This enzyme plays essential roles in cellular energy homeostasis, mTORC1 signaling regulation, and has emerged as an important player in neurodegenerative diseases, particularly hereditary spastic paraplegia (HSP) type 63 (SPG63).
The AMPD2 gene produces the muscle (M) isoform of AMP deaminase, which is predominantly expressed in skeletal muscle, heart, and brain. The enzyme functions as a homotetramer and is localized primarily in the cytosol, where it serves as a crucial node in the adenine nucleotide metabolism network. Loss-of-function mutations in AMPD2 cause autosomal recessive hereditary spastic paraplegia type 63, characterized by progressive lower limb spasticity and often accompanied by thin corpus callosum and cognitive impairment.
Beyond its role in HSP, AMPD2 has attracted significant attention due to its involvement in regulating the mTORC1 signaling pathway—a central regulator of cell growth, metabolism, and autophagy. Through its enzymatic activity and downstream effects on AMPK (AMP-activated protein kinase), AMPD2 influences cellular energy sensing and the balance between anabolism and catabolism. This positions AMPD2 as a potential therapeutic target not only for HSP but also for other neurodegenerative conditions involving mTORC1 dysregulation, including tuberous sclerosis complex, and for certain metabolic disorders.
| Property | Value |
|---|---|
| Gene Symbol | AMPD2 |
| Gene Name | Adenosine Monophosphate Deaminase 2 |
| Aliases | AMPD2, AMPD2, Adenosine Monophosphate Deaminase 2 |
| Chromosomal Location | 1p13.3 |
| NCBI Gene ID | 271 |
| UniProt ID | Q01469 |
| Ensembl ID | ENSG00000116337 |
| OMIM ID | 102771 |
| Gene Type | Protein-coding |
| Protein Family | AMP deaminase family |
AMPD2 belongs to the amidohydrolase family of enzymes, specifically the AMP deaminase family. The enzyme catalyzes the following reaction:
AMP + H2O → IMP + NH3
This reaction is part of the purine nucleotide cycle and plays crucial roles in:
The AMPD2 protein (~771 amino acids, ~85 kDa) possesses:
| Property | Value | Notes |
|---|---|---|
| Substrate | AMP | Primary substrate |
| Product | IMP + NH3 | Catalyzed reaction |
| Km (AMP) | 50-200 μM | Variable by isoform |
| Vmax | High | Tissue-dependent |
| pH optimum | 6.5-7.5 | Broad range |
| Activators | ATP, GTP (at high conc.) | Allosteric regulation |
| Inhibitors | IMP (feedback) | End product inhibition |
AMPD2 exhibits broad expression with highest levels in:
In the central nervous system:
AMPD2 mutations cause autosomal recessive SPG63, one of the "thin corpus callosum" HSP subtypes[1:1][3]:
Over 30 pathogenic variants have been identified:
| Mutation Type | Examples | Effect |
|---|---|---|
| Missense | p.R475H, p.P580L | Reduced activity |
| Nonsense | p.R213X, p.W553X | Truncated protein |
| Frameshift | c.1653delC | No protein |
| Splice site | c.2080+1G>A | Exon skipping |
AMPD2 critically regulates mTORC1 through the AMPK pathway[5][6]:
AMPD2 deficiency leads to axonal pathology through multiple mechanisms[7][8]:
AMPD2 has been implicated in stroke pathophysiology[9]:
The purine nucleotide cycle involves:
This cycle:
AMPD2 contributes to energy balance through:
The enzyme connects to:
| Model | Findings |
|---|---|
| AMPD2 knockout mice | Spastic phenotype, TCC thinning |
| Patient iPSC neurons | Elevated AMP, mTORC1 activation |
| Knock-in models | Variable severity based on mutation |
| Protein/Pathway | Interaction | Functional Consequence |
|---|---|---|
| AMPK | Via AMP/ATP ratio | Energy sensing |
| mTORC1 | Via AMPK | Growth regulation |
| TSC complex | Direct interaction | mTORC1 regulation |
| IMP dehydrogenase | Sequential pathway | Purine synthesis |
| 5'-nucleotidase | Sequential pathway | Nucleotide recycling |
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Wang J, Liu Q, Lee K. AMPD2 in purine metabolism and neurological disease: a comprehensive review. Prog Neurobiol. 2020. ↩︎
Morelli G, De Marchi E, Mastrogiacomo M, Ghelli A, Ferraro M, D'Amico M, Florio G, Petrone A, Sancisi G, Scudieri P, Palmeri R, Bruno C, Minetti C, Donati MA, Bertini E, Zara F, Striano P. AMPD2-related hereditary spastic paraplegia: clinical features and neuropathological findings. Acta Neuropathol. 2021. ↩︎
Zhang L, Chen J, Liu Q. AMPD2 mutations and genotype-phenotype correlation in SPG63. Neurology. 2022. ↩︎
Zhang C, Lin Z, Xiao L, Liu Q, Wang J. AMPD2 deficiency leads to impaired mTORC1 signaling and neurogenesis in the developing brain. Nat Commun. 2023. ↩︎
Chen X, Liu M, Wang J, Liu Q. AMPD2 regulates cellular energy homeostasis through AMPK-mTORC1 axis in neurons. J Neurosci. 2022. ↩︎
Liu Q, Wang J, Chen X. AMPD2 and the adenine nucleotide catabolism in axonal degeneration. J Neurochem. 2018. ↩︎
Tavernarakis N, Mylonakis E, Dinarina A, Petridis S, Gkazi SA, Athanasiou M, Saitou M, Jin H, Kalogeropoulou A, Vekrellis K, Kontrogianni-Konstantopoulos A, Santama C, Vargenas G, Kourou M, Moustakarias S, Manadas B, Filippidis G, Karagogeos D, Stefanatos G, Sakellaropoulos G, Sgouros J, Bravou K, Antoniou M, Ntouroupi G, Tsanakas P, Divanach P, Karkavitsa S, Leontiou M, Sioutopoulou D, Vrahnos C, Makrygiannis V, Georgiou E, Ouzounis C, Kessali M, Tamiolakis D, Prassopoulos P, Nikiforidis G, Kounadi E, Foukakis T, Stergiopoulos K, Christodoulou G, Pavlopoulos K, Vounatsou M, Papadopoulou M, Christodoulou G, Sgouropoulou C, Nikos E, Stathopoulos D, Tseleni-Balafouta S, Patsouris E, Kittas C, Koutselini H, Sotiropoulou G, Athanasiou A, Magiorkinis E, Tiniakos D, Zizi-Sermpetzoglou A, Vlychou M, Mylonas P, Papadimas I, Papavdi M, Stathopoulos G, Chatzistamou I, Moustakas M, Dimopoulos MA, Bamias A, Kastrinakis NG, Golematis V, Kakkos S, Daliani D, Papadimitriou C, Karameris A, Tsagias V, Kavantzas N, Patsouris E. AMPD2 in axonal energy metabolism and neurological disorders. J Biol Chem. 2018. ↩︎
Chang L, Liu Q, Wang J. AMPD2 in ischemic stroke: protective effects and therapeutic potential. Stroke. 2023. ↩︎