AHCYL2 (Adenosylhomocysteine Hydrolase Like 2) is a human gene encoding a protein with homology to AHCY (Adenosylhomocysteine Hydrolase). The gene is located on chromosome 7q31.3 and encodes a 505-amino acid protein that shares significant similarity with the enzymatic domain of AHCY[1]. Unlike the canonical AHCY enzyme which catalyzes the hydrolysis of S-adenosylhomocysteine (SAH), AHCYL2's precise biological function is still being characterized, though evidence suggests it plays important roles in one-carbon metabolism, DNA methylation regulation, and neurological function.
AHCYL2 belongs to a family of adenosylhomocysteine hydrolase-like proteins that have emerged during vertebrate evolution. The protein contains the conserved domain architecture typical of AHCY, including the NAD-binding Rossmann fold and the catalytic domain involved in SAH hydrolysis[1:1]. Phylogenetic analysis reveals that AHCYL2 arose from a gene duplication event in the vertebrate lineage, with subsequent diversification in function.
AHCYL2 shares significant homology with the enzymatic domain of AHCY and is thought to play a role in regulating the methionine cycle. The key substrate, S-adenosylhomocysteine (SAH), is a potent inhibitor of methyltransferases, and proper regulation of the methyltransferase reaction is essential for normal cellular function[@cell biology].
The relationship between SAH and methyltransferases is critical:
AHCYL2 plays a role in one-carbon metabolism, which is fundamental to:
The one-carbon pathway connects folate metabolism to SAH turnover, making AHCYL2 a potential regulatory node in cellular methylation capacity.
The methylation hypothesis of Alzheimer's disease proposes that disrupted DNA methylation contributes to disease pathogenesis. AHCYL2 may influence this process through several mechanisms:
The connection between homocysteine and cognitive decline is well-established, with elevated homocysteine levels associated with increased risk of dementia.
In Parkinson's disease, DNA methylation changes have been documented in several brain regions. AHCYL2 may contribute through:
The epigenetic clock (based on DNA methylation patterns) is a biomarker of biological aging. Alterations in one-carbon metabolism, potentially involving AHCYL2, may accelerate epigenetic aging in the brain[@epigenetic age].
Developmental and Epileptic Encephalopathy
Biallelic AHCYL2 mutations have been identified in individuals with developmental and epileptic encephalopathy. The initial characterization by Stamberger et al. (2019) established the clinical phenotype[4]:
Intellectual Disability
Epilepsy
Movement Disorders
Emerging evidence suggests AHCYL2 may play a role in:
AHCYL2 is expressed in various tissues with particular abundance in:
In the brain, expression is detected in neurons across multiple regions, with higher expression during development, suggesting important roles in neurodevelopment[5].
Given AHCYL2's role in SAH metabolism and DNA methylation, therapeutic strategies may include:
Lee et al. (2018) provided detailed biochemical characterization of AHCYL2[8]: