<div class="infobox infobox-protein"> | Property | Value | |---|---| | Protein Name | Heterogeneous Nuclear Ribonucleoprotein Q (HNRNPQ) | | Gene | [HNRNPQ](/genes/hnrnpq) | | UniProt | [P61956](https://www.uniprot.org/uniprot/P61956) | | PDB | 4X25, 5EPI | | Molecular Weight | ~62 kDa | | Subcellular Localization | Nucleus, Cytoplasm | | Protein Family | hnRNP family (SYNCRIP/hnRNP Q) | | Aliases | SYNCRIP, hnRNP Q, GRY-RBP | </div>
Overview
HNRNPQ (Heterogeneous Nuclear Ribonucleoprotein Q), also known as SYNCRIP (Synaptotagmin-binding Cytoplasmic RNA-Interacting Protein), is a 527-amino acid RNA-binding protein that plays critical roles in post-transcriptional gene regulation. It is a member of the hnRNP family and is involved in various aspects of RNA metabolism including alternative splicing, mRNA stability, translation regulation, and RNA transport[@kim_stress_2016][@maurer_2017].
The protein is ubiquitously expressed with high levels in brain, particularly in synaptic regions where it regulates the local translation of synaptic mRNAs. HNRNPQ has been implicated in neurodegenerative diseases including ALS, Parkinson's disease, Huntington's disease, and Alzheimer's disease[@fukuda_rbm_2015][@saito_rbm_2015][@cho_hnrnpq_2019].
N-terminal acidic domain: Contains multiple acidic amino acid clusters that mediate protein-protein interactions and regulatory functions.
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HNRNPQ Protein
<div class="infobox infobox-protein"> | Property | Value | |---|---| | Protein Name | Heterogeneous Nuclear Ribonucleoprotein Q (HNRNPQ) | | Gene | [HNRNPQ](/genes/hnrnpq) | | UniProt | [P61956](https://www.uniprot.org/uniprot/P61956) | | PDB | 4X25, 5EPI | | Molecular Weight | ~62 kDa | | Subcellular Localization | Nucleus, Cytoplasm | | Protein Family | hnRNP family (SYNCRIP/hnRNP Q) | | Aliases | SYNCRIP, hnRNP Q, GRY-RBP | </div>
Overview
HNRNPQ (Heterogeneous Nuclear Ribonucleoprotein Q), also known as SYNCRIP (Synaptotagmin-binding Cytoplasmic RNA-Interacting Protein), is a 527-amino acid RNA-binding protein that plays critical roles in post-transcriptional gene regulation. It is a member of the hnRNP family and is involved in various aspects of RNA metabolism including alternative splicing, mRNA stability, translation regulation, and RNA transport[@kim_stress_2016][@maurer_2017].
The protein is ubiquitously expressed with high levels in brain, particularly in synaptic regions where it regulates the local translation of synaptic mRNAs. HNRNPQ has been implicated in neurodegenerative diseases including ALS, Parkinson's disease, Huntington's disease, and Alzheimer's disease[@fukuda_rbm_2015][@saito_rbm_2015][@cho_hnrnpq_2019].
N-terminal acidic domain: Contains multiple acidic amino acid clusters that mediate protein-protein interactions and regulatory functions.
Three RNA recognition motifs (RRMs): RRM1, RRM2, and RRM3 in the central region bind specific RNA sequences. These RRMs have distinct RNA-binding preferences that allow HNRNPQ to recognize diverse target mRNAs.
C-terminal glycine-rich region: Involved in protein-protein interactions with other hnRNP proteins and RNA granule components.
Nuclear localization signal (NLS): Media nuclear-cytoplasmic shuttling, allowing HNRNPQ to function in both compartments.
Protein-Protein Interactions
HNRNPQ interacts with:
TDP-43 (TARDBP): In stress granules and RNA complexes[@kim_stress_2016]
FUS: RNA granule component in ALS
SMN complex: Involved in snRNP assembly
Synaptotagmin: Synaptic vesicle protein
Various mRNA decay factors: Including AU-rich element binding proteins
Normal Function in the Nervous System
HNRNPQ functions in multiple neuronal processes:
Alternative Splicing: Regulates splice site selection for numerous neuronal transcripts. It modulates the inclusion/exclusion of exons in pre-mRNAs encoding synaptic proteins[@bauer_2018].
mRNA Stability: Binds to AU-rich elements (AREs) in mRNA 3' untranslated regions, regulating mRNA half-life and degradation rates.
Translation Regulation: Controls translation initiation and elongation, particularly for synaptic mRNAs localized in neuronal processes.
RNA Transport: Part of RNA granules that transport mRNA from the cell body to synapses, enabling localized protein synthesis at synaptic terminals.
Synaptic Function: Regulates expression of synaptic proteins including AMPA and NMDA receptor subunits. HNRNPQ is highly enriched in synaptic fractions and is important for dendritic spine morphology and function[@bauer_2018].
Neural Development: Important for neuronal differentiation and axon guidance.
HNRNPQ is highly expressed in brain, particularly in synaptic fractions.
Role in Neurodegeneration
Amyotrophic Lateral Sclerosis (ALS)
HNRNPQ is centrally implicated in ALS pathogenesis:
Stress Granule Pathology: HNRNPQ is recruited to stress granules in ALS models and patient tissue[@kim_stress_2016][@maurer_2017]. Mutations in prion-like domains of TDP-43 and FUS alter stress granule dynamics and sequester HNRNPQ.
TDP-43 Interaction: HNRNPQ physically interacts with TDP-43 in RNA granules. TDP-43 pathology in ALS affects HNRNPQ distribution and function.
Splicing Defects: Altered splicing of HNRNPQ targets in ALS, including transcripts encoding mitochondrial function and cytoskeletal proteins.
Loss of Function: Reduced HNRNPQ levels in ALS motor neurons may contribute to RNA processing deficits.
Parkinson's Disease
In dopaminergic neurons, HNRNPQ plays important roles: