ANXA11 Human

What are the main biological functions of ANXA11?

ANXA11 participates in several cellular processes through its calcium-dependent phospholipid-binding capabilities. Based on structural and functional analyses, ANXA11 appears to have important roles in:

• Calcium signaling: The protein undergoes conformational changes in response to calcium binding, which may regulate its interactions with other proteins such as ALG-2 (apoptosis-linked gene-2 protein) and S100A6 (calcyclin) .

• Biomolecular condensate formation: The N-terminal domain, particularly its intrinsically disordered regions, contributes to granule formation properties . These granule-forming tendencies are primarily triggered by structural disorder rather than RNA binding.

• Molecular tethering: Evidence supports the hypothesis that ANXA11 functions as a molecular tether, with its N-terminal domain playing a distinct and specific role in this process .

• Membrane interactions: Like other annexin family members, ANXA11 can bind to phospholipid membranes in a calcium-dependent manner, which may be relevant for various cellular processes.

How are ANXA11 variants classified and what is their prevalence in different populations?

ANXA11 variants can be classified based on their location within the protein structure:

• N-terminal LCD (Low Complexity Domain) variants: These occur in the intrinsically disordered N-terminal region, with several hotspots identified at residues 36, 38, and 40 .

• C-terminal ANX domain variants: These occur in the structured core domain of the protein .
  The prevalence of ANXA11 variants shows significant ethnic differences:

• Korean population: A study of 882 sporadic ALS (sALS) patients found 16 different ANXA11 variants in 26 patients, with a total variant frequency of approximately 2.9% . All carriers were sporadic ALS cases rather than familial ALS (fALS).

• Chinese population: Studies showed a variant frequency of about 2.3% in Chinese sALS patients .

• European population: Research on European cohorts identified ANXA11 variants accounting for 1.3% in fALS and 1.4% in sALS .
  These findings suggest that ANXA11 variants are more common in Asian populations (Korean and Chinese) compared to European populations. Additionally, the low rate of fALS in Koreans compared to Europeans might explain why no fALS patients harboring ANXA11 variants were found in the Korean cohort .

How do specific ANXA11 mutations contribute to ALS pathogenesis?

ANXA11 mutations appear to contribute to ALS pathogenesis through distinct mechanisms depending on their location within the protein:

• N-terminal LCD variants (e.g., p.G38R and p.D40G): These variants increase the protein's propensity for aggregation . The location of these mutations within the helical region (residues 38-59) may disrupt the normal structural transitions of this region. Since this helix appears crucial for protein-protein interactions, mutations could alter ANXA11's interaction landscape .

• C-terminal ANX domain variants (e.g., p.H390P and p.R456H): These variants primarily alter calcium responses rather than aggregation properties . Since calcium binding regulates the conformational changes and function of annexins, these mutations likely disrupt ANXA11's normal calcium-dependent activities.
  The differential pathomechanisms translate into distinct clinical features. For example, approximately half of the patients carrying N-terminal LCD variants were diagnosed with ALS-FTD (ALS with frontotemporal dementia), particularly those with variants at residues 36 and 40 . This suggests that N-terminal mutations may have more pronounced effects on cognitive function.
  Furthermore, ALS patients with ANXA11 variants typically display a later age of onset (average 64.2 years) compared to the general Korean ALS patient population (average 60.4 years) . Within the ANXA11 variant carriers, those with LCD variants had a significantly older age of onset than those with ANX domain variants .

What methodologies are most effective for studying ANXA11 structure-function relationships?

Multiple complementary approaches have proven valuable for studying ANXA11 structure-function relationships:

• X-ray crystallography: This has been successfully used to determine the structure of the C-terminal domain of ANXA11. The structure superposes with corresponding regions of other annexins within 1.2 Å, confirming the conserved nature of this domain .

• Spectroscopic methods: Various spectroscopic techniques have been employed to characterize the structural properties of ANXA11, particularly to confirm the presence of a helical structure in the region spanning residues 38-59 of both wild-type and mutated ANXA11 .

• Small-angle X-ray scattering (SAXS): This technique has been used to determine the relative orientation of the N-terminal domain compared to the C-terminal core domain in a calcium-dependent manner .

• Computational prediction tools: Advanced computational tools like RosETTAFold and AlphaFold have been used to predict regions with RNA-binding properties and granule-forming tendencies . These predictions help guide experimental design by identifying regions of interest.

• Genetic analyses: Methods such as whole-exome sequencing, comprehensive multi-gene panel analysis, and Sanger sequencing have been used to identify and confirm ANXA11 variants in ALS patients . These analyses typically involve filtering out variants with allele frequencies >0.01 based on public databases such as gnomAD and population-specific databases.

• Functional studies with patient-derived cells: These provide insights into the pathogenic potential of specific variants. For example, studies have been performed to assess the functional consequences of hotspot variants like p.P36R and p.D40G using ALS-FTD patient cells .

How do researchers evaluate the clinical significance of novel ANXA11 variants?

Evaluating the clinical significance of novel ANXA11 variants involves a multifaceted approach:

• Variant classification: All identified variants should be classified according to established guidelines, such as those from the American College of Medical Genetics and Genomics, the Association for Molecular Pathology, and ClinGen recommendations . This classification typically categorizes variants as pathogenic, likely pathogenic, variants of uncertain significance (VUS), likely benign, or benign.

• Population frequency analysis: Variants are filtered based on allele frequencies in public databases like gnomAD and population-specific databases (e.g., KRGDB for Korean variants). Typically, variants with allele frequencies >0.01 are filtered out as they are unlikely to be disease-causing .

• Segregation analysis: For familial cases, determining whether the variant segregates with disease in affected family members can provide evidence for pathogenicity.

• Clinical correlation: Detailed clinical characterization of patients carrying specific variants can reveal distinctive phenotypic patterns. This includes:

  • Age of onset

  • Site of initial symptoms (spinal or bulbar)

  • Presence of other neurological manifestations (e.g., FTD, multisystem proteinopathies)

  • Disease progression rates using validated scales like ALSFRS-R (revised ALS functional rating scale)

  • Survival periods

• Functional validation: In vitro and/or in vivo studies to assess the functional consequences of variants. For ANXA11, this might include:

  • Aggregation propensity assays

  • Calcium response measurements

  • Structural analyses of variant proteins

  • Effects on biomolecular condensate formation

  • Consequences for molecular tethering functions

What are the domain-specific clinical manifestations of ANXA11 variants in ALS patients?

Research has revealed distinct clinical manifestations associated with variants in different domains of ANXA11:

• N-terminal LCD variants:

  • Significantly older age of onset compared to patients with ANX domain variants

  • Higher prevalence of ALS-FTD (approximately 50% of patients), particularly those with variants at residues 36 and 40

  • Potentially different disease progression patterns, though longitudinal studies with larger cohorts are needed to confirm this

• C-terminal ANX domain variants:

  • Earlier age of onset compared to LCD variant carriers

  • Potentially different cognitive profiles, with possibly lower rates of FTD comorbidity
    These domain-specific clinical differences align with the distinct functional consequences observed in experimental studies, where LCD variants primarily affect aggregation propensity while ANX domain variants alter calcium responses . This suggests that different pathomechanisms may underlie the clinical heterogeneity observed in ANXA11-associated ALS.

How can researchers resolve the apparent structural contradictions in ANXA11 models?

Computational prediction tools like AlphaFold and RosETTAFold have yielded somewhat divergent models for ANXA11 structure, presenting a challenge for researchers. These contradictions can be approached methodologically:

What role does ANXA11 play in biomolecular condensate formation and function?

ANXA11's role in biomolecular condensate formation represents an exciting frontier in research:

• Structural basis: The N-terminal domain of ANXA11, with its intrinsically disordered regions and proline-rich sequences, appears primed for participation in phase separation phenomena . Computational predictions indicate that ANXA11's granule-forming tendencies are primarily triggered by structural disorder rather than RNA binding .

• Calcium regulation: Since ANXA11 is a calcium-dependent protein, changes in calcium concentration likely regulate its condensate-forming properties. This suggests a potential mechanism for dynamic control of ANXA11-containing biomolecular condensates in response to cellular signaling events.

• Disease relevance: The increased aggregation propensity observed with N-terminal variants (e.g., p.G38R and p.D40G) might reflect aberrant phase separation behavior. This could disrupt normal condensate dynamics, leading to the formation of pathological aggregates or the impairment of physiological condensate functions.

• Membrane coupling: Recent evidence suggests that ANXA11 biomolecular condensates may facilitate protein-lipid phase coupling on lysosomal membranes . This could be crucial for understanding ANXA11's role in cellular physiology and pathology.
  Methodologically, researchers investigating this aspect of ANXA11 biology should consider:

• In vitro phase separation assays with purified wild-type and mutant ANXA11

• Live-cell imaging to track condensate dynamics

• Proteomics approaches to identify ANXA11's interaction partners within condensates

• Manipulating cellular calcium levels to observe effects on ANXA11 condensate properties

How can ethnic differences in ANXA11 variant distributions inform personalized medicine approaches for ALS?

The observed ethnic differences in ANXA11 variant frequencies and distributions provide important insights for personalized medicine:

• Population-specific screening strategies: The higher frequency of ANXA11 variants in Asian populations (Korean, Chinese) compared to European populations suggests that ANXA11 screening might be particularly important in Asian ALS patients.

• Variant interpretation: Different populations may harbor distinct variant spectra, requiring population-specific approaches to variant interpretation. For instance, a variant that is rare in one population might be relatively common in another, affecting its likely pathogenicity.

• Clinical management: Domain-specific clinical features of ANXA11 variants might inform clinical management. For example, patients with N-terminal LCD variants might benefit from earlier screening for cognitive impairment given the higher prevalence of ALS-FTD in this group .

• Therapeutic development: Understanding population-specific variant distributions could guide the development of targeted therapies. Approaches aimed at correcting specific types of ANXA11 dysfunction (e.g., aggregation versus calcium response) might be prioritized differently in various populations based on the predominant variant types.
  Methodologically, researchers should:

• Establish comprehensive population-specific databases of ANXA11 variants

• Conduct large-scale genotype-phenotype correlation studies across diverse populations

• Develop functional assays that reflect population-specific variant effects

• Integrate genetic findings with other biomarkers to improve prognostication and treatment selection

What are the optimal approaches for analyzing ANXA11 disease progression in clinical studies?

Analyzing ANXA11-associated disease progression requires rigorous methodological approaches:

What experimental systems best model ANXA11-associated pathology?

Several experimental systems offer complementary advantages for modeling ANXA11-associated pathology:

• Patient-derived cells: Fibroblasts, induced pluripotent stem cells (iPSCs), and iPSC-derived motor neurons from patients carrying ANXA11 variants provide physiologically relevant cellular contexts for studying disease mechanisms . These systems maintain the patient's genetic background, which may contain important modifier genes.

• CRISPR-engineered cell lines: Introducing specific ANXA11 mutations into otherwise isogenic backgrounds enables precise assessment of variant effects without confounding genetic factors.

• In vitro biochemical systems: Purified recombinant wild-type and mutant ANXA11 proteins can be used to study:

  • Structural changes using techniques like circular dichroism and SAXS

  • Calcium binding properties

  • Membrane interaction dynamics

  • Phase separation behavior

  • Protein-protein interactions

• Animal models: While not mentioned in the provided search results, transgenic animals expressing human ANXA11 variants could provide insights into in vivo consequences, particularly for understanding:

  • Motor neuron degeneration

  • Cognitive impairment

  • Age-dependent phenotypes

  • Response to potential therapeutic interventions

• In silico models: Computational approaches combining structural predictions, molecular dynamics simulations, and systems biology can generate testable hypotheses about ANXA11 function and dysfunction . The combination of RosETTAFold and AlphaFold predictions has already provided valuable insights into ANXA11 structure. When selecting experimental systems, researchers should consider the specific aspects of ANXA11 biology they aim to investigate and choose models accordingly. A multi-model approach is likely to yield the most comprehensive understanding of ANXA11-associated pathology.