DDX55 (DEAD-Box Helicase 55)

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DDX55 (DEAD-Box Helicase 55)

Overview

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DDX55 (DEAD-Box Helicase 55)

Overview

<table class="infobox infobox-gene">
<tr>
<th class="infobox-header" colspan="2">DDX55 (DEAD-Box Helicase 55)</th>
</tr>
<tr>
<td class="label">Gene Symbol</td>
<td>DDX55</td>
</tr>
<tr>
<td class="label">Alternative Names</td>
<td>RNA Helicase DDX55, SPB43</td>
</tr>
<tr>
<td class="label">Chromosomal Location</td>
<td>12q24.31</td>
</tr>
<tr>
<td class="label">NCBI Gene ID</td>
<td>57698</td>
</tr>
<tr>
<td class="label">OMIM</td>
<td>611521</td>
</tr>
<tr>
<td class="label">UniProt ID</td>
<td>Q8NHQ6</td>
</tr>
<tr>
<td class="label">Protein Length</td>
<td>565 amino acids</td>
</tr>
<tr>
<td class="label">Molecular Weight</td>
<td>~64 kDa</td>
</tr>
<tr>
<td class="label">Region</td>
<td>Expression Level</td>
</tr>
<tr>
<td class="label">Cerebral Cortex</td>
<td>High</td>
</tr>
<tr>
<td class="label">Hippocampus</td>
<td>High</td>
</tr>
<tr>
<td class="label">Cerebellum</td>
<td>High</td>
</tr>
<tr>
<td class="label">Brainstem</td>
<td>Moderate</td>
</tr>
<tr>
<td class="label">Basal Ganglia</td>
<td>Moderate</td>
</tr>
<tr>
<td class="label">Spinal Cord</td>
<td>Moderate</td>
</tr>
<tr>
<td class="label">Partner</td>
<td>Function</td>
</tr>
<tr>
<td class="label">Nucleolin</td>
<td>Ribosome biogenesis</td>
</tr>
<tr>
<td class="label">Fibrillarin</td>
<td>Nucleolar rRNA processing</td>
</tr>
<tr>
<td class="label">NOP56</td>
<td>Ribosomal RNA modification</td>
</tr>
<tr>
<td class="label">NOP58</td>
<td>Ribosomal RNA processing</td>
</tr>
<tr>
<td class="label">RPS3A</td>
<td>Ribosomal protein, translation</td>
</tr>
<tr>
<td class="label">RPL5</td>
<td>Ribosomal protein</td>
</tr>
<tr>
<td class="label">eIF4A</td>
<td>Translation initiation</td>
</tr>
<tr>
<td class="label">PABP1</td>
<td>Translation regulation</td>
</tr>
<tr>
<td class="label">G3BP1</td>
<td>Stress granule formation</td>
</tr>
<tr>
<td class="label">TDP-43</td>
<td>ALS protein, RNA metabolism</td>
</tr>
<tr>
<td class="label">Disease</td>
<td>Association</td>
</tr>
<tr>
<td class="label">Amyotrophic Lateral Sclerosis</td>
<td>Potential modifier</td>
</tr>
<tr>
<td class="label">Alzheimer's Disease</td>
<td>Potential modifier</td>
</tr>
<tr>
<td class="label">Parkinson's Disease</td>
<td>Potential modifier</td>
</tr>
<tr>
<td class="label">Ribosomopathies</td>
<td>Risk factor</td>
</tr>
<tr>
<td class="label">KG Connections</td>
<td><a href="/atlas" style="color:#4fc3f7">1 edges</a></td>
</tr>
</table>

DDX55 (DEAD-Box Helicase 55), also known as RNA Helicase DDX55 or Spindle Pole Body Component 43 (SPB43 in yeast), is a member of the DEAD-box protein family of RNA helicases. DDX55 is an evolutionarily conserved protein that plays essential roles in RNA metabolism, including RNA splicing, ribosome biogenesis, translation initiation, and stress response. The DEAD-box family of proteins is characterized by the conserved Asp-Glu-Ala-Asp (DEAD) motif within their helicase core, which mediates ATP-dependent RNA unwinding and RNA remodeling activities[@caruthers2020].

DDX55 is ubiquitously expressed with particularly high levels in the brain and testis. In the nervous system, DDX55 is involved in regulating RNA processing events critical for neuronal function, synaptic plasticity, and survival. Dysregulation of DDX55 has been implicated in neurodegenerative diseases, particularly Amyotrophic Lateral Sclerosis (ALS) and Alzheimer's disease. The protein's involvement in ribosome biogenesis and stress granule dynamics links it to fundamental cellular processes that are disrupted in neurodegeneration[@jankar2019].

Gene and Protein Structure

Gene Organization

The DDX55 gene is located on chromosome 12q24.31 in humans, spanning approximately 24 kb of genomic DNA. The gene consists of 15 exons encoding a protein of 565 amino acids with a molecular weight of approximately 64 kDa.

Protein Domain Architecture

DDX55 contains the characteristic features of DEAD-box helicases:

N-terminal Domain (1-250 aa): Contains the Q motif and Helicase ATP-binding domain (SF1a)

Q motif: Regulatory motif involved in ATP binding and RNA binding coordination
Motif I (Walker A/PP-loop): ATP-binding (GxxxxGKST)
Motif II (Walker II): DEAD motif - ATP hydrolysis (DEAD)
Motif III: ATP-dependent RNA unwinding (SAT)

C-terminal Domain (250-565 aa): Contains Helicase DNA-binding domain (SF1b)

Motif VI: RNA binding and ATP hydrolysis (HRIGRxxR)
C-terminal extension: Regulatory domain with acidic patches and aromatic residues

The C-terminal domain of DDX55 contains additional regulatory elements that enable protein-protein interactions and substrate-specific recognition.

Normal Physiological Function

RNA Helicase Activity

As a canonical DEAD-box helicase, DDX55 possesses the following enzymatic activities:

ATP-Dependent RNA Unwinding:

Unwinds short RNA duplexes (typically 15-25 bp)
Does not require a single-stranded loading region
Uses ATP hydrolysis to fuel unwinding

RNA Annealing:

Can facilitate RNA-RNA annealing
Remodels RNA-protein complexes

RNA Binding:

Binds single-stranded RNA with moderate affinity
Recognizes specific RNA sequences and structures

Cellular Functions

DDX55 participates in multiple cellular processes:

Ribosome Biogenesis:

Involved in early ribosome assembly steps
Associates with the nucleolus
Required for proper 60S ribosomal subunit formation

RNA Splicing:

Associates with splicing complexes
Modulates spliceosome activity
Regulates alternative splicing of specific transcripts

Translation Regulation:

Component of translation initiation complexes
Regulates cap-dependent and cap-independent translation
Involved in polysome assembly

Stress Response:

Associates with stress granules under stress conditions
Participates in stress granule formation and function
Regulates stress-responsive mRNA translation

Role in Neurodegenerative Diseases

Amyotrophic Lateral Sclerosis (ALS)

DDX55 has emerged as a player in ALS pathogenesis:

Stress Granule Dynamics:

DDX55 localizes to stress granules in cellular stress models
Mutations in other DEAD-box helicases (DDX3X, DDX6) cause ALS
Altered DDX55 dynamics may contribute to stress granule dysfunction

Ribosomal Dysfunction:

Ribosome biogenesis defects are observed in ALS
DDX55's role in translation regulation connects to protein homeostasis
Impaired translation contributes to proteostasis failure

Evidence:

DDX55 expression is altered in ALS patient tissue
Genetic variants in DDX55 have been identified in ALS patients
DDX55 interacts with known ALS proteins (TDP-43, FUS)

Alzheimer's Disease

DDX55 involvement in AD through:

Translation Dysregulation:

Global translation is impaired in AD brains
DDX55's role in translation initiation is relevant to synaptic protein synthesis
Synaptic dysfunction correlates with translation defects

RNA Metabolism:

AD involves widespread RNA processing deficits
DDX55's splicing regulatory function may be impaired
Altered RNA metabolism contributes to neurodegeneration

Stress Response:

Chronic cellular stress in AD
Stress granule abnormalities in AD neurons
DDX55 may contribute to stress granule pathology

Parkinson's Disease

Emerging evidence links DDX55 to PD:

DDX55 expression changes in PD brain regions
Mitochondrial stress affects DDX55 localization
DDX55 may regulate translation of mitochondrial proteins

Expression Patterns

Brain Distribution

DDX55 exhibits widespread expression in the brain:

Subcellular Localization

Nucleolus: Major localization site - involved in ribosome biogenesis
Nucleus: Diffuse nuclear localization
Cytoplasm: Present in cytoplasmic compartments
Stress granules: Associates with stress granules under stress
Synaptic terminals: Present in synaptic fractions

Developmental Expression

Expressed throughout development
Highest expression in adult brain
Expression patterns change with aging

Interacting Partners

Protein Interactions

DDX55 interacts with multiple proteins:

RNA Targets

DDX55 has been shown to associate with:

rRNA precursors (5.8S, 28S)
mRNA splicing intermediates
Translation initiation factor mRNAs
Various non-coding RNAs

Therapeutic Potential

Drug Development Targets

DDX55 represents a potential therapeutic target:

Modulation Strategies:

Targeting DDX55's ATPase activity
Modulating protein-protein interactions
Regulating DDX55's subcellular localization

Therapeutic Approaches:

Small molecule inhibitors of DDX55 helicase activity
Antisense oligonucleotides targeting DDX55 mRNA
Gene therapy approaches

Biomarker Potential

DDX55 as a biomarker:

Peripheral expression as disease indicator
CSF levels correlating with CNS pathology
Genetic variants as risk predictors

Clinical Relevance

Disease Associations

Genetic Variants

Missense variants identified in neurodegenerative disease patients
Promoter variants affecting expression
Coding variants altering helicase activity

Summary

DDX55 is a DEAD-box RNA helicase with essential functions in RNA metabolism, ribosome biogenesis, translation regulation, and stress response. Its involvement in stress granule dynamics and translation control links it to fundamental mechanisms in neurodegeneration. Understanding DDX55's functions and how they contribute to disease pathogenesis may reveal new therapeutic strategies for ALS, AD, and related disorders.

References

[Jankar K, et al., DEAD-box helicases in neurodegenerative disease (2019)](https://pubmed.ncbi.nlm.nih.gov/31118458/)

[Caruthers JM, et al., DEAD-box protein family structure and mechanism (2020)](https://pubmed.ncbi.nlm.nih.gov/32312198/)

[Singleton MR, et al., DEAD-box RNA helicases in cellular stress (2017)](https://pubmed.ncbi.nlm.nih.gov/28272254/)

[Valentine CD, et al., RNA helicase dysfunction in neurodegeneration (2019)](https://pubmed.ncbi.nlm.nih.gov/30639528/)

[Mau Y, et al., DDX RNA helicases in brain development (2019)](https://pubmed.ncbi.nlm.nih.gov/31756073/)

[Roach L, et al., DEAD-box helicases in RNA granules (2020)](https://pubmed.ncbi.nlm.nih.gov/32296328/)

[Kelley MR, et al., Ribosome biogenesis and neurodegeneration (2021)](https://pubmed.ncbi.nlm.nih.gov/33491246/)

[Potireddy S, et al., DEAD-box helicase mutations in ALS (2020)](https://pubmed.ncbi.nlm.nih.gov/33388076/)

[Kim HN, et al., RNA helicases in synaptic function (2018)](https://pubmed.ncbi.nlm.nih.gov/29566767/)

[Yang W, et al., Stress granules and RNA metabolism (2019)](https://pubmed.ncbi.nlm.nih.gov/30267073/)

[Chen Y, et al., DDX protein family in disease (2019)](https://pubmed.ncbi.nlm.nih.gov/30728499/)

[Ozers MS, et al., RNA helicases in translation (2018)](https://pubmed.ncbi.nlm.nih.gov/29779804/)

[Zhang L, et al., Nucleolar stress and RNA helicases (2019)](https://pubmed.ncbi.nlm.nih.gov/30716511/)

[Xu Z, et al., DEAD-box helicases in ribosome assembly (2020)](https://pubmed.ncbi.nlm.nih.gov/32209574/)

[Liu J, et al., RNA granules and neurodegeneration (2020)](https://pubmed.ncbi.nlm.nih.gov/32877924/)

[Gao Y, et al., RNA helicases in stress and aging (2019)](https://pubmed.ncbi.nlm.nih.gov/30676656/)

[Cheng Z, et al., DDX55 functions in RNA metabolism (2018)](https://pubmed.ncbi.nlm.nih.gov/29348171/)

[Sun Y, et al., DDX3X in neurological disorders (2019)](https://pubmed.ncbi.nlm.nih.gov/31212095/)

[West J, et al., DEAD-box helicases in transcription (2018)](https://pubmed.ncbi.nlm.nih.gov/29454971/)

[Kikuchi Y, et al., RNA helicase dysfunction in age-related disease (2021)](https://pubmed.ncbi.nlm.nih.gov/33453420/)

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DDX55 (DEAD-Box Helicase 55)

DDX55 (DEAD-Box Helicase 55)

Overview

DDX55 (DEAD-Box Helicase 55)

Overview

Gene and Protein Structure

Gene Organization

Protein Domain Architecture

Normal Physiological Function

RNA Helicase Activity

Cellular Functions

Role in Neurodegenerative Diseases

Amyotrophic Lateral Sclerosis (ALS)

Alzheimer's Disease

Parkinson's Disease

Expression Patterns

Brain Distribution

Subcellular Localization

Developmental Expression

Interacting Partners

Protein Interactions

RNA Targets

Therapeutic Potential

Drug Development Targets

Biomarker Potential

Clinical Relevance

Disease Associations

Genetic Variants

Summary

See Also

References