| Feature | SUMF2 / pFGE | SUMF1 / FGE comparison | Evidence |
|---|---|---|---|
| Human gene / protein identity | **SUMF2** encodes **pFGE** (paralog of formylglycine-generating enzyme), also described as **inactive C\u03b1-formylglycine-generating enzyme 2** and **sulfatase-modifying factor 2** | **SUMF1** encodes **FGE**, the active formylglycine-generating enzyme required for sulfatase activation | (pqac-00000005, pqac-00000008, pqac-00000011) |
| Evolutionary relationship | Shares ~**47% homology/48% sequence identity** with SUMF1/FGE and belongs to the same FGE/DUF323 protein family | FGE is the catalytically active paralog; both proteins are structurally closely related | (pqac-00000005, pqac-00000008) |
| Molecular size / precursor organization | Glycosylated human pFGE crystallized as a secretory-pathway protein; crystal model contained residues **28\u2013294**, with C-terminal residues beyond 294 not resolved; N-glycosylation seen at **Asn-191** | Human FGE is a **40 kDa, 374-residue glycoprotein** with a cleavable ER signal peptide (residues 1\u201332), mature region 33\u2013374, and N-glycosylation at **Asn-141** | (pqac-00000008, pqac-00000014, pqac-00000000) |
| Overall structure / fold | Crystal structure solved at **1.86 \u00c5**; adopts the characteristic **FGE fold**, a novel low-secondary-structure fold that became the structural paradigm for DUF323 proteins | FGE has a highly similar fold; structural similarity helped define why pFGE is inactive despite preserving substrate-binding architecture | (pqac-00000008, pqac-00000009, pqac-00000013) |
| Subcellular localization | **ER-resident** protein in the early secretory pathway; functions where newly synthesized sulfatases are matured | FGE is also **ER-resident** and is the active sulfatase-modifying enzyme in the ER | (pqac-00000008, pqac-00000012, pqac-00000006) |
| Enzymatic activity status | **No formylglycine-generating activity** detected; binds sulfatase-derived peptide substrates but is catalytically inactive | FGE is the **sole enzyme** responsible for generating C\u03b1-formylglycine (FGly) in mammalian sulfatases | (pqac-00000008, pqac-00000005, pqac-00000006) |
| Substrate recognition | Binds sulfatase peptides bearing the FGE recognition motif; likely recognizes the same sulfatase maturation context as FGE | FGE recognizes the conserved sulfatase motif centered on **CxPxR** within the catalytic domain and converts the target cysteine to FGly | (pqac-00000008, pqac-00000005, pqac-00000006) |
| Primary biochemical role | Functions as an **inactive regulator/antagonist** of sulfatase activation rather than as a catalyst; evidence suggests it can reduce effective sulfatase activation by counterbalancing FGE | FGE catalyzes the post-translational oxidation needed to activate all cellular sulfatases | (pqac-00000012, pqac-00000005, pqac-00000006) |
| Key binding partners | Binds **sulfatase substrates/peptides** and likely interacts with **SUMF1/FGE**; structural analysis suggests capacity for **heterodimerization** with FGE; may also participate in ER quality-control interactions | FGE interacts with sulfatase substrates and ER quality-control/trafficking factors including **PDI, ERp44, ERGIC-53, ERp57** | (pqac-00000015, pqac-00000005, pqac-00000000) |
| Oligomeric behavior | Crystal asymmetric unit contains a **homodimer**; buried surface/contact geometry suggested possible biological significance and raised the possibility of **FGE-pFGE heterodimers** | FGE was proposed to form heterodimers with pFGE based on the close structural match | (pqac-00000008, pqac-00000015) |
| Calcium-binding features | Contains **two buried calcium-binding sites** that appear structure-stabilizing rather than catalytic | FGE likewise contains two calcium ions stabilizing the fold | (pqac-00000008, pqac-00000015, pqac-00000013) |
| Disulfide-bond features | Conserved internal disulfide bond between **Cys-156 and Cys-290** stabilizes the fold | FGE preserves the homologous stabilizing disulfide and also contains additional cysteines, including catalytically important active-site cysteines absent from pFGE functionally | (pqac-00000015, pqac-00000013) |
| Catalytic-site distinction from FGE | Retains a sulfatase-binding cleft but lacks the catalytic machinery that makes FGE active; major differences cluster near the putative reaction center | FGE has the active catalytic center that supports oxygen-dependent FGly generation | (pqac-00000009, pqac-00000013) |
| Domains / family annotations supported by literature | Member of the **FGE/DUF323 family** with the characteristic **FGE fold**; literature supports the same family/domain assignment as UniProt | Same family, catalytically active representative | (pqac-00000008, pqac-00000009) |
| Biological functions inferred/observed | Modulates global **sulfatase activity**, thereby affecting sulfated substrate turnover and signaling; proposed to regulate the balance of sulfatase activation in the ER | FGE is essential for activation of all sulfatases, influencing lysosomal degradation, steroid metabolism, extracellular matrix remodeling, and signaling through HSPG-editing sulfatases | (pqac-00000012, pqac-00000005, pqac-00000007) |
| Pathways / downstream biology | Through regulation of sulfatases, pFGE is linked to **glycosaminoglycan/heparan sulfate sulfation status**, extracellular matrix remodeling, and growth factor pathways such as **FGF/Wnt/BMP-related** signaling; zebrafish work supports a role in developmental timing via altered HSPG sulfation | FGE positively enables the same sulfatase-dependent pathways by permitting sulfatase activation | (pqac-00000012, pqac-00000011, pqac-00000007) |
| Disease / translational relevance | Human direct disease causality is less established than for SUMF1, but altered SUMF2 expression has been reported in recent association studies and plasma proteomic analyses; mechanistically it is relevant because increased SUMF2 could inhibit SUMF1-enhanced sulfatase activity | **SUMF1 mutations cause multiple sulfatase deficiency (MSD)**, a severe multisystem lysosomal disorder | (pqac-00000003, pqac-00000013, pqac-00000011) |


*Table: This table summarizes the core properties of human SUMF2/pFGE, including identity, localization, structure, activity, interactions, and biological roles, with side-by-side comparison to SUMF1/FGE where that clarifies function. It is useful as a compact evidence-based reference for functional annotation of SUMF2.*