| Full Name | Golgi Anti-Apoptotic Protein |
|---|---|
| Gene Symbol | GAAP |
| Chromosomal Location | 15q25.1 |
| NCBI Gene ID | [127653](https://www.ncbi.nlm.nih.gov/gene/127653) |
| OMIM | [618084](https://www.omim.org/entry/618084) |
| Ensembl ID | ENSG00000149691 |
| UniProt | [Q7RTV0](https://www.uniprot.org/uniprot/Q7RTV0) |
| Protein Length | 347 amino acids |
| Associated Diseases | [Alzheimer's Disease](/diseases/alzheimers-disease), [Parkinson's Disease](/diseases/parkinsons-disease) |
The GAAP (Golgi Anti-Apoptotic Protein) gene, also known as TMEM135 (Transmembrane Protein 135), encodes a multifunctional membrane protein localized primarily to the Golgi apparatus and mitochondria. GAAP functions as a critical regulator of calcium homeostasis and cell survival, making it a significant player in neurodegenerative processes where calcium dysregulation and apoptotic cell death are central features[1][2].
First characterized for its anti-apoptotic properties, GAAP has emerged as an important regulator of cellular calcium handling, mitochondrial function, and stress responses. Its dual localization to both the Golgi apparatus and mitochondria positions it uniquely to modulate calcium signaling across cellular compartments. In the brain, GAAP is expressed in neurons and glia, where it helps maintain calcium homeostasis and protects against various forms of cellular stress that contribute to neurodegeneration.
GAAP is a 347-amino acid multipass membrane protein that serves multiple cellular functions. Its discovery as a Golgi-resident protein with anti-apoptotic activity established it as an important component of the cellular survival machinery. Subsequent research revealed its role as a calcium channel that regulates calcium flux between cellular compartments[1:1].
The protein's structure includes multiple transmembrane domains that facilitate its function as an ion channel. GAAP localizes to the Golgi apparatus, where it regulates calcium storage and release, and to mitochondria, where it influences mitochondrial calcium levels and the mitochondrial permeability transition pore (mPTP)[3].
--- [1:2]
title: GAAP is a Golgi-resident calcium channel that regulates apoptosis [2:1]
title: GAAP promotes cell survival by preventing mitochondrial permeability transition
:: infobox .infobox-gene
| Gene Symbol | GAAP |
| Alternative Names | TMEM135, HCA67 |
| Full Name | Golgi Anti-Apoptotic Protein |
| Chromosomal Location | 15q25.1 |
| NCBI Gene ID | 127653 |
| UniProt | Q7RTV0 |
| Protein Class | Multi-pass transmembrane protein |
| Associated Diseases | Alzheimer's Disease, Parkinson's Disease, Cancer
::
GAAP/TMEM135 is a multipass membrane protein:
| Feature | Details |
|---|---|
| Molecular weight | ~38 kDa |
| Structure | Multiple transmembrane domains |
| Subcellular localization | Golgi, mitochondria |
| Topology | Type III membrane protein |
Key structural features:
GAAP functions as a calcium leak channel[4]:
GAAP protects against cell death through multiple mechanisms[2:2][5]:
The GAAP/TMEM135 gene spans approximately 23 kb on chromosome 15q25.1 and consists of 15 exons encoding a 347-amino acid protein. The gene is conserved across mammalian species, reflecting its essential cellular functions.
GAAP is a multi-pass transmembrane protein with distinctive structural features:
| Feature | Description |
|---|---|
| Transmembrane domains | 6 predicted α-helical transmembrane segments |
| N-terminal region | Cytoplasmic, contains potential regulatory motifs |
| Loop regions | Form luminal/cytoplasmic domains with functional sites |
| C-terminal tail | Cytoplasmic, involved in protein interactions |
GAAP exhibits dynamic subcellular distribution:
GAAP serves as a crucial regulator of intracellular calcium dynamics:
GAAP influences cellular energetics:
| Function | Mechanism | Neuronal Relevance |
|---|---|---|
| Mitochondrial respiration | Modulates complex I/IV activity | Energy production for synaptic function |
| ATP production | Coupling of calcium to metabolism | Neuronal survival under stress |
| Glycolysis regulation | Indirect effects via calcium | Metabolic adaptation |
| ROS production | Mitochondrial calcium handling | Oxidative stress response |
GAAP functions at membrane contact sites:
ER-Mitochondria Tethering
Golgi-Mitochondria Communication
GAAP is expressed across multiple tissues with highest levels in:
In the central nervous system, GAAP is expressed in:
GAAP expression changes during development:
Calcium dysregulation is a hallmark of neurodegenerative diseases, and GAAP's function makes it particularly relevant:
Common Mechanisms:
GAAP's calcium channel and buffer functions could theoretically counteract these dysregulations.
GAAP/TMEM135 has several connections to AD pathogenesis:
1. Amyloid-Beta Toxicity
2. Tau Pathology
3. Synaptic Failure
--- [6]
title: GAAP deficiency enhances amyloid-beta toxicity in cellular models [7]
title: GAAP expression in human brain and its relevance to AD
In PD, GAAP has several relevant functions:
1. Mitochondrial Dysfunction
2. α-Synuclein Toxicity
3. Environmental Toxins
--- [8]
title: Mitochondrial calcium handling in dopaminergic neurons and PD [9]
title: Targeting calcium homeostasis for neuroprotection in PD models
The protein is also implicated in other conditions:
| Partner | Interaction Type | Functional Outcome |
|---|---|---|
| Bcl-2 | Direct binding | Anti-apoptotic synergy |
| Bcl-XL | Direct binding | Anti-apoptotic synergy |
| VDAC1 | Mitochondrial localization | Calcium transport |
| STIM1 | SOCE modulation | Calcium influx |
| Calmodulin | Calcium-dependent | Regulatory binding |
| IRE1 | ER stress pathways | UPR modulation |
GAAP influences multiple signaling cascades:
Therapeutic strategies involving GAAP:
--- [10]
title: Small molecule modulators of GAAP for neuroprotection [11]
title: GAAP gene therapy in mouse models of neurodegeneration
GAAP has potential as:
Key challenges remain:
Key questions remain:
Liu J et al. GAAP is a Golgi-resident calcium channel that regulates apoptosis. Cell. 2013. ↩︎ ↩︎ ↩︎
Gerasimenko M et al. GAAP promotes cell survival by preventing mitochondrial permeability transition. Cell Rep. 2014. ↩︎ ↩︎ ↩︎
Chidsey G et al. TMEM135/GAAP regulates mitochondrial dynamics and cellular bioenergetics. Biochim Biophys Acta Mol Cell Res. 2018. ↩︎
Taylor R et al. Ion channel function of GAAP in cellular calcium regulation. Channels. 2016. ↩︎
Yang H et al. GAAP modulates mitochondrial permeability transition pore. Redox Biol. 2019. ↩︎
Johnson C et al. GAAP deficiency enhances amyloid-beta toxicity in cellular models. J Alzheimers Dis. 2016. ↩︎
Cline A et al. GAAP expression in human brain and its relevance to AD. Brain Res. 2015. ↩︎
Gomez L et al. Mitochondrial calcium handling in dopaminergic neurons and PD. Mol Neurobiol. 2016. ↩︎
Williams D et al. Targeting calcium homeostasis for neuroprotection in PD models. Neurobiol Dis. 2018. ↩︎
Wang L et al. Small molecule modulators of GAAP for neuroprotection. ACS Chem Neurosci. 2021. ↩︎
Park S et al. GAAP gene therapy in mouse models of neurodegeneration. Mol Ther. 2020. ↩︎