S100Z Human

What is S100Z and how is it classified within the S100 protein family?

S100Z is a calcium-binding protein belonging to the S-100 family, also known as S100 calcium-binding protein Z. It contains 99 amino acids in its full-length form and functions as part of the larger S100 protein family . Like other S100 proteins, it possesses calcium-binding motifs including a C-terminal canonical EF-hand with high calcium-binding affinity and an N-terminal pseudo-EF-hand (S100-specific EF-hand) . This structure is characteristic of S100 proteins, which typically form homodimers or heterodimers with other family members. S100Z represents one of the more recently characterized members of this family, with its crystal structure having been solved only in recent years .

What is the structural characterization of human S100Z?

The X-ray crystal structure of human apo-S100Z (calcium-free form) has been solved and represents an important advancement in understanding this protein . Structurally, it follows the general S100 protein pattern with:

• A calcium-free (apo) structure that differs from calcium-bound forms

• A dimer configuration that is physiologically relevant

• Structural elements including α-helices and calcium-binding loops

• Structural similarity to other S100 family members despite sequence differences

Comparison between the human apo-S100Z structure and the zebrafish calcium-bound S100Z (which is the closest in sequence) reveals important insights about calcium-dependent conformational changes . Unlike some other S100 proteins such as calcium-bound S100A4, human apo-S100Z does not form a superhelical arrangement in crystal structures, suggesting that calcium binding plays a fundamental role in triggering quaternary structure formation in several S100 proteins .

What are the current known biological functions of S100Z?

Research has linked S100Z to several potential biological functions, although its precise roles remain less characterized compared to other S100 family members:

• Expression in specific tissues, particularly in the olfactory system, suggests tissue-specific functions

• Association with cancer and inflammatory diseases, indicating potential roles in pathological processes

• Likely involvement in calcium-dependent signaling pathways typical of S100 proteins

• Potential protein-protein interactions, particularly with annexins, as observed with other S100 family members

How does calcium binding affect the structural and functional properties of S100Z?

Calcium binding induces significant conformational changes in S100 proteins, and S100Z likely follows this pattern. The structural comparison between human apo-S100Z and modeled holo-S100Z (calcium-bound) has revealed important differences similar to those observed in other S100 family members .

Based on structural studies:

• Calcium binding typically exposes hydrophobic surfaces that facilitate target protein interactions

• The transition from apo to holo states involves rearrangements of helices, particularly helix III

• Calcium-bound S100Z may form higher-order oligomeric structures (tetramers, hexamers) as seen with other S100 proteins

• The precise calcium affinity of S100Z and its calcium-dependent interactions with target proteins remain areas requiring further research

These conformational changes are crucial for understanding S100Z functions since calcium binding serves as a molecular switch that regulates interactions with target proteins and subsequent signaling events.

What is the expression pattern of S100Z in human tissues and how does it compare to other species?

S100Z shows interesting expression patterns that differ between species:

The expression of S100Z in the amphibian olfactory system differs from mammals, as it is exclusive to the main olfactory system in Xenopus and not associated with the vomeronasal organ as in mammals . This suggests evolutionary divergence in S100Z function despite the presence of separate accessory olfactory systems in both classes of animals.

How does S100Z interact with annexins and other binding partners within the cell?

S100 proteins are known to interact with annexins, forming functional complexes that contribute to their biological functions . For S100Z specifically:

• Analysis of protein interaction networks shows that annexins generally exhibit a preference for interaction with S100 proteins

• S100Z likely engages in both calcium-dependent and calcium-independent interactions

• The molecular basis for these interactions may involve regions with increased mobility, such as calcium-binding loops, the hinge region connecting subdomains, helix III, and the terminal regions

• The presence of intrinsically disordered protein regions (IDPRs) may contribute to binding promiscuity and functional polymorphism

The global interactome analysis of annexin-S100 proteins reveals complex interaction networks, with S100 proteins typically showing preference for interactions within their family, while annexins preferentially interact with S100 proteins . Further research is needed to identify the specific binding partners of S100Z and characterize these interactions at the molecular level.

What are the optimal methods for expressing and purifying recombinant human S100Z?

For researchers working with S100Z, several methodological approaches have proven successful:

• Expression System: Escherichia coli has been successfully used for recombinant expression of human S100Z with high purity (>95%)

• Purification Tags: His-tag purification approaches are effective, with commercially available recombinant S100Z typically including tags such as: MGSSHHHHHHS SGLVPRGSHM

• Purification Methods: Combination of affinity chromatography (using His-tag) followed by size exclusion chromatography is recommended

• Quality Control: SDS-PAGE analysis showing protein at approximately 13.7kDa confirms successful purification

For structural studies, careful attention to calcium conditions is essential, as demonstrated in crystallization studies of apo-S100Z . Removing calcium completely for apo-structure studies or ensuring precise calcium concentrations for holo-structure investigations is critical for meaningful results.

What experimental approaches are recommended for investigating S100Z function in cellular systems?

When investigating S100Z function, researchers should consider multiple complementary approaches:

• Immunohistochemistry: Successfully used to identify S100Z expression patterns in tissues, particularly useful for studying distribution in specialized tissues like olfactory epithelium

• Protein-Protein Interaction Studies:

  • Co-immunoprecipitation to identify binding partners

  • Yeast two-hybrid screening for detecting potential interactions

  • Surface plasmon resonance (SPR) to quantify binding affinities

• Calcium-Binding Studies:

  • Isothermal titration calorimetry (ITC) to determine binding affinities

  • Circular dichroism (CD) spectroscopy to monitor structural changes upon calcium binding

• Functional Assays:

  • Cell-based assays focusing on known S100 protein functions (regulation of cell proliferation, differentiation, migration)

  • Investigation of potential roles in inflammatory responses and cancer pathways

For cellular localization studies, both standard immunofluorescence and advanced microscopy techniques can provide insights into S100Z distribution and potential calcium-dependent relocalization events.

How can researchers effectively study S100Z expression patterns in human tissues?

Investigating S100Z expression patterns requires careful methodological considerations:

• Tissue Selection: Based on current knowledge, focus should include:

  • Olfactory epithelium and related sensory tissues

  • Tissues associated with inflammatory responses

  • Cancer tissues showing altered S100 protein expression

• Detection Methods:

  • RNA analysis (qPCR, RNA-seq) for transcript expression

  • Protein detection using specific antibodies validated for human S100Z (118 antibodies are reportedly available)

  • In situ hybridization to identify cell-specific expression patterns

• Controls and Validation:

  • Use of markers for specific cell types (as done in the Xenopus study with TP63 and cytokeratin type II to distinguish cell types)

  • Comparison with other S100 family members to establish specificity

  • Inclusion of known positive and negative control tissues

The approach used in the Xenopus study, combining whole mount and slice preparations with multiple markers for cell identification, provides a methodological framework that can be adapted for human tissue studies .

What evidence links S100Z to cancer and inflammatory conditions?

While S100Z remains less characterized than other S100 family members, emerging research suggests potential roles in pathological conditions:

• Research has linked S100Z to conditions including cancer and inflammatory diseases

• Alterations in S100Z expression or function may influence cancer cell behavior

• Other S100 family members are well-established biomarkers and functional contributors to cancer progression and inflammation

Further investigations are needed to establish:

• The specific cancer types where S100Z plays significant roles

• Mechanisms by which S100Z contributes to pathological processes

• Potential utility as a diagnostic or prognostic biomarker

• Therapeutic implications of targeting S100Z in disease contexts

How do intrinsically disordered regions of S100Z contribute to its functional diversity?

The functional diversity of S100 proteins, including S100Z, may be explained through the protein intrinsic disorder perspective:

• While S100 proteins are considered ordered proteins structurally, they demonstrate functional characteristics typical of intrinsically disordered proteins (IDPs)

• Specific regions in S100 proteins show increased mobility and disorder propensity:

  • Calcium-binding loops

  • The linker loop ("hinge") connecting protein subdomains

  • Helix III

  • N- and C-termini

These intrinsically disordered protein regions (IDPRs) likely contribute to:

• Binding promiscuity with multiple, often unrelated partners

• Functional polymorphism allowing participation in diverse cellular processes

• Structural adaptability upon calcium binding or interaction with binding partners

The presence of these disorder-prone regions in S100Z would provide mechanistic explanations for its ability to engage in multiple functional interactions despite having a generally ordered structural core .

What challenges exist in solving the crystal structure of human S100Z, and how were they overcome?

The crystallographic determination of human apo-S100Z structure presented significant challenges:

• Standard molecular replacement procedures proved difficult despite the availability of structures from other S100 family members

• Multiple models and different software tools were required, with only one approach ultimately succeeding

• Interestingly, the successful template model was one with one of the lowest sequence identities with S100Z among the S100 family in the apo state

This experience highlights important methodological considerations for structural studies of S100 proteins:

• Sequence identity alone may not predict structural similarity

• Multiple molecular replacement approaches should be attempted when working with challenging structures

• The calcium-binding state (apo vs. holo) significantly impacts structure and must be carefully controlled

The successful determination of the apo-S100Z structure represents an important achievement in completing the structural characterization of the S100 family, as highlighted by the researchers who described it as "conquering one of the last S100 family strongholds" .

How does the structure of human S100Z compare to other S100 family members?

Comparative structural analysis reveals important insights about S100Z relative to other family members:

The comparison between human apo-S100Z and zebrafish calcium-bound S100Z (its closest sequence homolog) reveals important insights about calcium-dependent conformational changes . Human apo-S100Z does not form the superhelical arrangement observed in zebrafish calcium-bound S100Z and human calcium-bound S100A4, supporting the critical role of calcium in triggering quaternary structure formation in S100 proteins .