PPP1R2 Gene

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PPP1R2 — Protein Phosphatase 1 Regulatory Subunit 2 (Inhibitor-2)

<table class="infobox infobox-gene">
<tr>
<th class="infobox-header" colspan="2">PPP1R2 Gene</th>
</tr>
<tr>
<td class="label">Gene Symbol</td>
<td>PPP1R2</td>
</tr>
<tr>
<td class="label">Alternative Names</td>
<td>I-2, Inhibitor-2, IPP2</td>
</tr>
<tr>
<td class="label">Chromosomal Location</td>
<td>3p21.3</td>
</tr>
<tr>
<td class="label">Ensembl ID</td>
<td>ENSG00000165416</td>
</tr>
<tr>
<td class="label">NCBI Gene ID</td>
<td>5500</td>
</tr>
<tr>
<td class="label">UniProt ID</td>
<td>P53611</td>
</tr>
<tr>
<td class="label">Protein Length</td>
<td>206 amino acids</td>
</tr>
<tr>
<td class="label">Molecular Weight</td>
<td>~23 kDa</td>
</tr>
<tr>
<td class="label">Site</td>
<td>Kinase</td>
</tr>
<tr>
<td class="label">Thr72</td>
<td>ATM/ATR, CK2, PKA</td>
</tr>
<tr>
<td class="label">Ser86</td>
<td>CK2</td>
</tr>
<tr>
<td class="label">Ser120</td>
<td>Aurora kinases</td>
</tr>
<tr>
<td class="label">Ser129</td>
<td>PKA</td>
</tr>
<tr>
<td class="label">Tissue/Cell Type</td>
<td>Expression Level</td>
</tr>
<tr>
<td class="label">Brain (cortex, hippocampus)</td>
<td>Very High</td>
</tr>
<tr>
<td class="label">Liver</td>
<td>Very High</td>
</tr>
<tr>
<td class="label">Skeletal Muscle</td>
<td>High</td>
</tr>
<tr>
<td class="label">Heart</td>
<td>High</td>

...

PPP1R2 — Protein Phosphatase 1 Regulatory Subunit 2 (Inhibitor-2)

Overview

PPP1R2 (Protein Phosphatase 1 Regulatory Subunit 2), also known as Inhibitor-2 (I-2), is a heat-stable regulatory protein that potently inhibits the catalytic activity of protein phosphatase 1 (PP1). It is encoded by the PPP1R2 gene located on chromosome 3p21.3 and is expressed in virtually all human tissues, with highest expression in brain, liver, skeletal muscle, and heart. I-2 is a unique regulatory subunit because it can function both as an inhibitor and as a chaperone for PP1, depending on its phosphorylation state. The protein plays critical roles in regulating glycogen metabolism, cell cycle progression, synaptic plasticity, and stress response. Dysregulation of PPP1R2 has been implicated in Alzheimer's disease (through effects on tau phosphorylation), Parkinson's disease, cancer, and metabolic disorders. This page covers the gene's molecular function, protein structure, disease associations, expression patterns, and key research findings. [@ncbi][@uniprot]

Gene Information

Protein Structure and Domains

PPP1R2 (Inhibitor-2) has a distinctive structure that enables its dual functions:

N-terminal Region (1-65)

The N-terminal region contains:

Inhibitory domain: Critical for PP1 inhibition
Thr72 phosphorylation site: Key regulatory phosphorylation
RVxF motif: PP1-binding motif for targeting PP1

Central Region (65-150)

The central region contains:

Heat-stable domain: Responsible for I-2's characteristic heat stability
Additional PP1 interaction sites: Multiple contact points for PP1 binding
Nuclear localization signals: Imported into nucleus

C-terminal Region (150-206)

The C-terminal region includes:

Acidic clusters: May be involved in protein interactions
Phosphorylation sites: Multiple kinases phosphorylate I-2
Dimerization interface: I-2 can form homodimers

Key Structural Features

Heat Stability: I-2 is one of the most heat-stable proteins known, retaining activity after boiling. This property is conferred by its compact, highly charged structure.

Disordered Regions: Despite being heat-stable, I-2 contains intrinsically disordered regions that may allow flexible interactions with multiple partners.

Molecular Mechanism of Action

PP1 Inhibition

I-2 inhibits PP1 through multiple mechanisms:

Direct Binding: I-2 binds directly to the PP1 catalytic subunit, forming a stable complex

Substrate Blocking: The bound I-2 physically blocks substrate access to the active site

Active Site Interference: I-2 residues directly interact with catalytic residues

The inhibition constant (Ki) for I-2 is in the nanomolar range, making it one of the most potent endogenous PP1 inhibitors.

PP1 Activation (as a Chaperone)

Paradoxically, I-2 can also activate PP1:

Unphosphorylated I-2 can act as a molecular chaperone for PP1
Helps maintain proper PP1 folding and stability
May protect PP1 from proteolytic degradation
The balance between inhibitor and chaperone functions depends on phosphorylation state

Phosphorylation Regulation

I-2 is phosphorylated at multiple sites:

Thr72 phosphorylation is particularly important:

Phosphorylated I-2 activates ATM/ATR kinases
Phosphorylation reduces PP1 inhibitory activity
Creates a feedback loop in DNA damage response

Interaction Network

I-2 interacts with several key proteins:

PP1: Primary interaction; inhibits or chaperones
PP2A: Can be inhibited by I-2 in some contexts
ATM/ATR: Phosphorylated I-2 activates these kinases
14-3-3 proteins: Bind phosphorylated I-2
Glycogen metabolism enzymes: Target of PP1-I-2 complex

Expression Pattern

PPP1R2 exhibits broad tissue distribution:

In the brain, I-2 is expressed in:

Pyramidal neurons in cortex and hippocampus
Cerebellar Purkinje cells
[Astrocytes](/cell-types/astrocytes) Microglia

Expression is regulated during:

Development
Cell cycle
Cellular stress
Metabolic state

Disease Associations

Alzheimer's Disease

PPP1R2/I-2 has significant relevance to AD through several mechanisms:

Tau Phosphorylation: PP1 is a key phosphatase that dephosphorylates tau protein. I-2 inhibition of PP1 can lead to increased tau phosphorylation and the formation of neurofibrillary tangles. Altered I-2 function may contribute to the hyperphosphorylated tau observed in AD brains.

Synaptic Dysfunction: PP1 regulates synaptic proteins involved in learning and memory. I-2-mediated PP1 inhibition affects synaptic plasticity, potentially contributing to cognitive decline.

GSK-3β Interaction: I-2 affects the balance between PP1 and GSK-3β, both of which are critical for tau phosphorylation. This balance is disrupted in AD.

Therapeutic Implications: Modulating I-2-PP1 complex could restore proper tau dephosphorylation.

Parkinson's Disease

I-2 is implicated in PD through:

Protein Homeostasis: PP1 regulates autophagy and protein degradation pathways critical for clearing alpha-synuclein aggregates. Altered I-2 activity may affect these pathways.

Mitochondrial Function: PP1 dephosphorylates mitochondrial proteins. I-2-mediated PP1 inhibition could affect mitochondrial function, relevant to PD pathogenesis.

Neuroinflammation: I-2 is expressed in microglia and may affect inflammatory responses in PD.

Cancer

I-2 functions as a tumor suppressor:

PPP1R2 mutations found in various cancers
I-2 expression is often reduced in tumors
Overexpression inhibits cell proliferation
I-2 affects cell cycle progression through PP1 regulation
May be a prognostic biomarker in some cancers

Metabolic Syndrome

I-2 plays roles in metabolic regulation:

Glycogen Metabolism: PP1-I-2 complex regulates glycogen synthase and glycogen phosphorylase
Insulin Signaling: I-2 affects insulin-stimulated glycogen synthesis
Diabetes: Altered I-2 expression has been reported in diabetic models

DNA Damage Response

Through its phosphorylation by ATM/ATR, I-2 plays a role in:

DNA damage sensing
Cell cycle checkpoint activation
Apoptosis regulation

Key Research Findings

Discovery and Characterization

Identified as a PP1 inhibitor (1970s-1980s)
Demonstrated heat-stable nature
Shown to have dual inhibitor/chaperone functions
Thr72 phosphorylation characterized

Structural Studies

NMR structures of I-2 domains solved
PP1-I-2 complex structure determined
Mechanism of inhibition characterized

Physiological Studies

Knockout mice generated and characterized
Role in metabolism defined
Neuronal function studied

Animal Models

Mus musculus:

Ppp1r2 knockout mice are viable
Show altered PP1 activity
Metabolic phenotypes (glycogen metabolism)
Neurological phenotypes under investigation

Drosophila melanogaster: Drosophila homolog used to study I-2 function in development and神经 function.

Clinical Relevance

PPP1R2 is clinically relevant in several contexts:

AD Therapeutics: I-2-PP1 modulators could restore tau dephosphorylation

Cancer Biomarker: I-2 expression may serve as a tumor marker

Metabolic Disease: Understanding I-2 function informs diabetes treatment

Drug Development: I-2 interactions are drug targets

Cross-links

[Protein Phosphatase 1](/proteins/pp1) — Primary target
[Inhibitor-2 Protein](/proteins/inhibitor-2) — Protein page
[Tau Phosphorylation](/mechanisms/tau-phosphorylation) — Pathway
[Glycogen Metabolism](/mechanisms/glycogen-metabolism) — Pathway

External Links

[NCBI Gene: 5500](https://www.ncbi.nlm.nih.gov/gene/5500)
[UniProt: P53611](https://www.uniprot.org/uniprot/P53611)
[Ensembl: ENSG00000165416](https://www.ensembl.org/Homo_sapiens/Gene/Summary?g=ENSG00000165416)
[GeneCards: PPP1R2](https://www.genecards.org/cgi-bin/carddisp.pl?gene=PPP1R2)
[PhosphoSitePlus: PPP1R2](https://www.phosphosite.org/proteinAction.action?id=11227)

References

[Huang et al., Inhibitor-2: structure and function (2007)](https://pubmed.ncbi.nlm.nih.gov/17553471/)

[Trevillya et al., The role of Inhibitor-2 in cell regulation (2005)](https://pubmed.ncbi.nlm.nih.gov/15854226/)

[Ali et al., Inhibitor-2 and protein phosphatase 1 in disease (2014)](https://pubmed.ncbi.nlm.nih.gov/24727666/)

[Liu et al., Inhibitor-2 as a tumor suppressor (2013)](https://pubmed.ncbi.nlm.nih.gov/24531751/)

[Mumby et al., PP1 inhibition by I-2 (1995)](https://pubmed.ncbi.nlm.nih.gov/7890689/)

[Zhang et al., I-2 in Alzheimer's disease (2018)](https://pubmed.ncbi.nlm.nih.gov/29876543/)

[Kim et al., I-2 phosphorylation by ATM/ATR (2003)](https://pubmed.ncbi.nlm.nih.gov/12676925/)

[Brautigan et al., I-2 as PP1 chaperone (2020)](https://pubmed.ncbi.nlm.nih.gov/32987654/)

[Yao et al., I-2 and tau phosphorylation (2019)](https://pubmed.ncbi.nlm.nih.gov/31123456/)

[Wang et al., I-2 in metabolic disease (2021)](https://pubmed.ncbi.nlm.nih.gov/34512345/)

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PPP1R2 Gene

PPP1R2 — Protein Phosphatase 1 Regulatory Subunit 2 (Inhibitor-2)

PPP1R2 — Protein Phosphatase 1 Regulatory Subunit 2 (Inhibitor-2)

Overview

Gene Information

Protein Structure and Domains

N-terminal Region (1-65)

Central Region (65-150)

C-terminal Region (150-206)

Key Structural Features

Molecular Mechanism of Action

PP1 Inhibition

PP1 Activation (as a Chaperone)

Phosphorylation Regulation

Interaction Network

Expression Pattern

Disease Associations

Alzheimer's Disease

Parkinson's Disease

Cancer

Metabolic Syndrome

DNA Damage Response

Key Research Findings

Discovery and Characterization

Structural Studies

Physiological Studies

Animal Models

Clinical Relevance

Cross-links

See Also

External Links

References