GDPD2 (Glycerophosphoinositol inositolphosphodiesterase GDPD2) is a membrane-bound enzyme that specifically hydrolyzes glycerophosphoinositol (GroPIns) into glycerol and inositol 1-phosphate. It functions as an ecto-enzyme with its catalytic domain oriented extracellularly, requiring millimolar Ca2+ as a cofactor. GDPD2 plays a critical role in promoting osteoblast differentiation and serves as a marker of osteoblast maturation. The protein localizes to the plasma membrane as a multi-pass membrane protein and colocalizes with actin filaments, suggesting involvement in cytoskeletal remodeling during cell differentiation.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0005886 plasma membrane | IBA GO_REF:0000033 | ACCEPT | Summary: Plasma membrane localization is well-supported by experimental evidence. GDPD2 is a multi-pass membrane protein with transmembrane segments that anchor it in the membrane, with its catalytic domain oriented extracellularly. UniProt and literature confirm this membrane localization is essential for its ecto-enzyme function. Reason: Strong experimental evidence from biochemical and cell biology studies confirms GDPD2 as a plasma membrane protein with multiple transmembrane passes. The extracellular orientation of the catalytic domain and requirement for membrane anchoring to process extracellular glycerophosphoinositol support this core cellular component annotation. Supporting Evidence: file:human/GDPD2/GDPD2-deep-research.md GDPD2 is a multi-pass membrane protein predominantly localized at the plasma membrane. Topology studies indicate that it spans the membrane multiple times, anchoring the protein at the cell surface. file:human/GDPD2/GDPD2-deep-research-falcon.md Experimental data indicate that GDPD2 is primarily localized to the plasma membrane, where it is embedded as a multi-pass transmembrane protein file:human/GDPD2/GDPD2-deep-research-falcon.md The integration of GDPD2 into lipid bilayers appears to be facilitated by multiple transmembrane domains, which confer both stability and the appropriate orientation necessary for catalytic activity. |
| GO:0008889 glycerophosphodiester phosphodiesterase activity | IBA GO_REF:0000033 | MODIFY | Summary: This term is correct but less specific than the actual enzymatic activity. GDPD2 has been experimentally characterized as having glycerophosphoinositol inositolphosphodiesterase activity (GO:0047394), which is a more specific child term that precisely describes its substrate specificity for glycerophosphoinositol. Reason: While GDPD2 does possess glycerophosphodiester phosphodiesterase activity, experimental evidence demonstrates it specifically acts on glycerophosphoinositol and not on other glycerophosphodiesters like glycerophosphocholine or glycerophosphoethanolamine. The more specific term GO:0047394 better captures this substrate specificity. Proposed replacements: glycerophosphoinositol inositolphosphodiesterase activity Supporting Evidence: file:human/GDPD2/GDPD2-deep-research.md This enzyme specifically hydrolyzes glycerophosphoinositol (GroPIns) into glycerol and inositol 1-phosphate, and notably does not act on related glycerophosphodiesters such as glycerophosphoinositol-4-phosphate, glycerophosphocholine, -ethanolamine, or -serine file:human/GDPD2/GDPD2-deep-research-falcon.md GDPD2 functions primarily as a glycerophosphoinositol inositolphosphodiesterase. Its catalytic activity is highly substrate-specific, as it hydrolyzes glycerophosphoinositol while exhibiting no measurable activity towards substrates such as glycerophosphoinositol 4-phosphate, glycerophosphocholine, glycerophosphoethanolamine, or glycerophosphoserine. |
| GO:0005737 cytoplasm | IEA GO_REF:0000044 | REMOVE | Summary: This annotation is misleading as GDPD2 is primarily a plasma membrane protein with its catalytic domain oriented extracellularly. While there may be some cytoplasmic association via its transmembrane segments or interaction with cytoskeletal elements, the primary and functionally relevant localization is the plasma membrane, not the cytoplasm. Reason: GDPD2 is a multi-pass transmembrane protein with its functional catalytic domain on the extracellular side of the plasma membrane. The cytoplasm annotation likely comes from automatic mapping but does not reflect the actual topology and functional localization of the protein. The plasma membrane annotation already captures the correct localization. Supporting Evidence: file:human/GDPD2/GDPD2-deep-research.md The catalytic domain resides on the extracellular side of the membrane, consistent with the finding that glycerophosphoinositol is hydrolyzed in the extracellular medium by overexpressed GDPD2 |
| GO:0005856 cytoskeleton | IEA GO_REF:0000044 | MODIFY | Summary: While GDPD2 colocalizes with actin filaments and may associate with the cytoskeleton, the more specific term GO:0005884 (actin filament) better captures this interaction. The broad cytoskeleton term is too general. Reason: Evidence indicates GDPD2 specifically colocalizes with actin filaments rather than the cytoskeleton in general. The protein appears to concentrate at sites of actin-rich membrane structures and influences cell morphology, suggesting a specific association with the actin cytoskeleton rather than other cytoskeletal components. Proposed replacements: actin filament Supporting Evidence: file:human/GDPD2/GDPD2-deep-research.md GDPD2 has been observed in the cytoplasm associated with the cytoskeleton, co-localizing with actin filaments. This suggests that GDPD2 may concentrate at sites of actin-rich membrane structures file:human/GDPD2/GDPD2-deep-research-falcon.md GDPD2 has also been implicated in the regulation of the actin cytoskeleton, an association that suggests a multifaceted role in cellular morphology and motility. |
| GO:0005886 plasma membrane | IEA GO_REF:0000120 | ACCEPT | Summary: This plasma membrane annotation is correct and consistent with experimental evidence. This IEA annotation independently supports the IBA annotation for the same term, confirming plasma membrane localization through different computational methods. Reason: Multiple lines of evidence including transmembrane domain predictions, experimental topology studies, and functional characterization all confirm GDPD2 as a plasma membrane protein. This annotation correctly captures a core cellular component for this protein. Supporting Evidence: file:human/GDPD2/GDPD2-deep-research.md GDPD2 is a multi-pass membrane protein predominantly localized at the plasma membrane file:human/GDPD2/GDPD2-deep-research-falcon.md Experimental data indicate that GDPD2 is primarily localized to the plasma membrane, where it is embedded as a multi-pass transmembrane protein |
| GO:0006629 lipid metabolic process | IEA GO_REF:0000002 | MODIFY | Summary: This broad term is correct but vague. GDPD2 specifically catalyzes the hydrolysis of glycerophosphoinositol, a glycerophospholipid metabolite. More specific terms like glycerophospholipid metabolic process (GO:0006650) or phospholipid catabolic process would be more informative. Reason: While GDPD2 is involved in lipid metabolism, its specific function is the catabolism of glycerophosphoinositol, a glycerophospholipid derivative. A more specific biological process term would better represent its actual metabolic role. Proposed replacements: glycerophospholipid metabolic process Supporting Evidence: file:human/GDPD2/GDPD2-deep-research.md GDPD2s unique lipid substrate specificity ties it to lipid metabolic processes, particularly the catabolism of glycerophosphoinositol lipids file:human/GDPD2/GDPD2-deep-research-falcon.md The metabolic activity of GDPD2, through its hydrolysis of glycerophosphoinositol, could also play a role in modulating the levels of lipid-derived signaling molecules. |
| GO:0008081 phosphoric diester hydrolase activity | IEA GO_REF:0000002 | MODIFY | Summary: This is a correct parent term for GDPD2s enzymatic activity, but too general. The more specific glycerophosphoinositol inositolphosphodiesterase activity (GO:0047394) should be used as it precisely describes the substrate specificity. Reason: GDPD2 does have phosphoric diester hydrolase activity, but experimental characterization has shown it specifically acts on glycerophosphoinositol. Using the more specific molecular function term provides better functional annotation. Proposed replacements: glycerophosphoinositol inositolphosphodiesterase activity Supporting Evidence: file:human/GDPD2/GDPD2-deep-research.md GDPD2 encodes an enzyme with glycerophosphoinositol inositolphosphodiesterase activity (EC 3.1.4.43) file:human/GDPD2/GDPD2-deep-research-falcon.md GDPD2 functions primarily as a glycerophosphoinositol inositolphosphodiesterase. Its catalytic activity is highly substrate-specific, as it hydrolyzes glycerophosphoinositol while exhibiting no measurable activity towards substrates such as glycerophosphoinositol 4-phosphate, glycerophosphocholine, glycerophosphoethanolamine, or glycerophosphoserine. |
| GO:0016787 hydrolase activity | IEA GO_REF:0000043 | MARK AS OVER ANNOTATED | Summary: This extremely broad term is correct but uninformative. GDPD2 has been experimentally characterized with specific glycerophosphoinositol inositolphosphodiesterase activity, which should be the primary molecular function annotation. Reason: While technically correct that GDPD2 is a hydrolase, this term is too general to be useful. The specific enzymatic activity (glycerophosphoinositol inositolphosphodiesterase) has been experimentally determined and should be the focus of molecular function annotations. Proposed replacements: glycerophosphoinositol inositolphosphodiesterase activity Supporting Evidence: file:human/GDPD2/GDPD2-deep-research.md This enzyme specifically hydrolyzes glycerophosphoinositol (GroPIns) into glycerol and inositol 1-phosphate file:human/GDPD2/GDPD2-deep-research-falcon.md GDPD2's structure is defined by the presence of a conserved phosphodiesterase domain that endows it with the enzymatic capacity to specifically hydrolyze glycerophosphoinositol. |
| GO:0046872 metal ion binding | IEA GO_REF:0000043 | MODIFY | Summary: This annotation is correct but could be more specific. GDPD2 specifically requires Ca2+ as a cofactor for its enzymatic activity. The more specific term calcium ion binding (GO:0005509) would be more informative. Reason: Experimental evidence shows GDPD2 specifically requires millimolar Ca2+ as a cofactor for its catalytic activity. The calcium ion binding annotation would more precisely represent this metal ion requirement. Proposed replacements: calcium ion binding Supporting Evidence: file:human/GDPD2/GDPD2-deep-research.md GDPD2 functions as an ecto-enzyme, requiring millimolar Ca2+ as a cofactor file:human/GDPD2/GDPD2-deep-research.md The active site of the GP-PDE domain requires divalent cations for catalysis – notably Ca2+ acts as a cofactor to facilitate bond cleavage |
| GO:0047394 glycerophosphoinositol inositolphosphodiesterase activity | IEA GO_REF:0000120 | ACCEPT | Summary: This annotation precisely captures the experimentally determined enzymatic activity of GDPD2. Multiple studies have confirmed that GDPD2 specifically hydrolyzes glycerophosphoinositol to produce glycerol and inositol 1-phosphate, with no activity on other glycerophosphodiesters. Reason: This is the most specific and accurate molecular function annotation for GDPD2. Experimental evidence clearly demonstrates this specific enzymatic activity (EC 3.1.4.43) with strict substrate specificity for glycerophosphoinositol. This represents the core molecular function of the protein. Supporting Evidence: file:human/GDPD2/GDPD2-deep-research.md This enzyme specifically hydrolyzes glycerophosphoinositol (GroPIns) into glycerol and inositol 1-phosphate, and notably does not act on related glycerophosphodiesters such as glycerophosphoinositol-4-phosphate, glycerophosphocholine, -ethanolamine, or -serine file:human/GDPD2/GDPD2-deep-research-falcon.md GDPD2 functions primarily as a glycerophosphoinositol inositolphosphodiesterase. Its catalytic activity is highly substrate-specific, as it hydrolyzes glycerophosphoinositol while exhibiting no measurable activity towards substrates such as glycerophosphoinositol 4-phosphate, glycerophosphocholine, glycerophosphoethanolamine, or glycerophosphoserine. |
| GO:0005884 actin filament | IEA GO_REF:0000107 | KEEP AS NON CORE | Summary: GDPD2 colocalizes with actin filaments according to literature and database annotations. This association may be related to its role in cell morphology changes during osteoblast differentiation, though this represents a secondary localization compared to its primary plasma membrane residence. Reason: While GDPD2 does colocalize with actin filaments, this is not its primary localization or core function. The protein is primarily a plasma membrane ecto-enzyme, and the actin association may be relevant for its effects on cell morphology during differentiation but is not essential for its enzymatic function. Supporting Evidence: file:human/GDPD2/GDPD2-deep-research.md In addition to the cell surface, GDPD2 has been observed in the cytoplasm associated with the cytoskeleton, co-localizing with actin filaments file:human/GDPD2/GDPD2-deep-research.md This suggests that GDPD2 may concentrate at sites of actin-rich membrane structures (e.g. ruffles or protrusions), potentially linking its enzymatic activity to cytoskeletal remodeling file:human/GDPD2/GDPD2-deep-research-falcon.md In addition to its presence in the plasma membrane, GDPD2 has been associated with the cytoplasm and the cytoskeleton, suggesting a dynamic distribution that may allow it to participate in the reorganization of cellular architecture |
| GO:0007015 actin filament organization | IEA GO_REF:0000107 | KEEP AS NON CORE | Summary: There is some evidence that GDPD2 influences cell morphology and cytoskeletal arrangement, particularly during osteoblast differentiation. However, this appears to be an indirect effect of its enzymatic activity rather than a direct role in actin organization. Reason: Changes in cell morphology were observed upon altering GDPD2 levels, suggesting involvement in cytoskeletal remodeling. However, this is likely a downstream effect of its lipid metabolic activity and role in differentiation rather than a direct function in actin organization. This represents a peripheral rather than core function. Supporting Evidence: file:human/GDPD2/GDPD2-deep-research.md GDPD2 has been associated with actin cytoskeleton organization, as changes in cell morphology and cytoskeletal arrangement were observed upon altering GDPD2 levels file:human/GDPD2/GDPD2-deep-research.md experiments noted GDPD2s influence on cell shape and morphology, supporting a role at the interface of the plasma membrane and the actin cytoskeleton file:human/GDPD2/GDPD2-deep-research-falcon.md GDPD2 has also been implicated in the regulation of the actin cytoskeleton, an association that suggests a multifaceted role in cellular morphology and motility. The remodeling of the actin cytoskeleton, which is essential for various aspects of cell behavior including migration and adhesion, appears to be influenced by GDPD2 activity |
| GO:0030027 lamellipodium | IEA GO_REF:0000107 | REMOVE | Summary: There is no strong experimental evidence specifically placing GDPD2 in lamellipodia. While GDPD2 colocalizes with actin and may be at membrane ruffles, specific lamellipodium localization has not been demonstrated experimentally. Reason: This annotation appears to be an over-interpretation based on actin colocalization. While GDPD2 may be present at actin-rich membrane structures, there is no direct evidence for specific lamellipodium localization. The plasma membrane and actin filament annotations already capture the relevant cellular localizations. Supporting Evidence: file:human/GDPD2/GDPD2-deep-research.md This suggests that GDPD2 may concentrate at sites of actin-rich membrane structures (e.g. ruffles or protrusions) |
| GO:0045669 positive regulation of osteoblast differentiation | IEA GO_REF:0000107 | ACCEPT | Summary: This annotation is strongly supported by experimental evidence. GDPD2 is upregulated during osteoblast maturation and overexpression promotes osteoblast differentiation with increased alkaline phosphatase activity and mineralization. This represents a core biological function of GDPD2. Reason: Multiple experimental studies demonstrate that GDPD2 promotes osteoblast differentiation. It is considered a marker of osteoblast maturation, and overexpression accelerates the osteogenic program. This is one of the best-characterized biological roles of GDPD2 and represents a core function. Supporting Evidence: file:human/GDPD2/GDPD2-deep-research.md Overexpression of GDPD2 (GDE3) in osteoblastic cells has been shown to promote osteoblast differentiation, evidenced by increased alkaline phosphatase activity and mineralized calcium deposition file:human/GDPD2/GDPD2-deep-research.md GDPD2 accelerates the program of osteoblast differentiation and growth file:human/GDPD2/GDPD2-deep-research-falcon.md In this context, GDPD2 has been shown to stimulate osteoblast differentiation and growth, a function that likely depends on its capacity to modulate the lipid microenvironment at the plasma membrane file:human/GDPD2/GDPD2-deep-research-falcon.md The acceleration of osteoblast differentiation observed upon the upregulation of GDPD2 provides direct evidence of its involvement in pathways critical to bone formation |
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Download this section (compressed HTML)Q: What is the physiological concentration of extracellular glycerophosphoinositol in bone tissue and how does it change during osteoblast differentiation?
Suggested experts: bone_biology, lipid_metabolism
Q: Does GDPD2 have any additional substrates beyond glycerophosphoinositol under specific cellular conditions?
Suggested experts: enzymology, biochemistry
Q: What are the downstream signaling effects of the inositol 1-phosphate product generated by GDPD2 activity?
Suggested experts: cell_signaling, phosphoinositide_biology
Q: Is GDPD2 activity regulated by post-translational modifications or protein-protein interactions during osteoblast differentiation?
Suggested experts: protein_biochemistry, bone_biology
Q: What is the functional significance of GDPD2 colocalization with actin filaments at the plasma membrane?
Suggested experts: cell_biology, cytoskeleton
Experiment: GDPD2 knockout mouse model to assess skeletal phenotype
Hypothesis: Loss of GDPD2 will result in decreased bone density and impaired osteoblast differentiation in vivo
Type: GENETIC_MANIPULATION
Experiment: Live-cell imaging of fluorescently-tagged GDPD2 during osteoblast differentiation
Hypothesis: GDPD2 localization and dynamics change during the transition from proliferating to differentiating osteoblasts
Type: CELL_BIOLOGY
Experiment: Mass spectrometry-based lipidomics to measure glycerophosphoinositol levels in GDPD2-overexpressing vs control cells
Hypothesis: GDPD2 overexpression will deplete extracellular glycerophosphoinositol pools and alter downstream lipid metabolites
Type: BIOCHEMISTRY
Experiment: Co-immunoprecipitation and proximity labeling to identify GDPD2 protein interaction partners
Hypothesis: GDPD2 forms complexes with cytoskeletal proteins or other membrane-associated signaling molecules
Type: PROTEOMICS
Experiment: Structure determination of GDPD2 catalytic domain by X-ray crystallography or cryo-EM
Hypothesis: Structural analysis will reveal the molecular basis for substrate specificity and calcium dependence
Type: STRUCTURAL_BIOLOGY
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