| Annotation category | Summary for human P4HA1 (UniProt P13674) | Supporting citations |
|---|---|---|
| Gene/protein identity | **P4HA1** encodes **prolyl 4-hydroxylase subunit alpha-1**, the predominant catalytic α(I) subunit of the main collagen prolyl 4-hydroxylase isoenzyme (**C-P4H-I**) in most tissues; it belongs to the collagen/prolyl 4-hydroxylase family. | (pqac-00000003, pqac-00000007) |
| Enzyme class & reaction | A **2-oxoglutarate/Fe(II)-dependent dioxygenase** that catalyzes **4-hydroxylation of peptidyl proline** to form **4-hydroxyproline**, especially in collagen/procollagen, a modification required for collagen triple-helix formation and stability. | (pqac-00000000, pqac-00000003, pqac-00000006) |
| Required cofactors/co-substrates & products | Catalysis requires **Fe2+**, **molecular oxygen**, **2-oxoglutarate/α-ketoglutarate**, and **ascorbate** to maintain the reduced iron state; the reaction yields hydroxylated substrate plus **succinate** and **CO2**. | (pqac-00000000, pqac-00000002, pqac-00000005, pqac-00000006) |
| Substrate specificity | Canonical substrates are proline residues in collagen **Gly-X-Y / X-Pro-Gly** contexts, especially motifs undergoing prolyl 4-hydroxylation during procollagen maturation. Reported non-collagen/collagen-like examples include **mannose-binding lectin (MBL)** and additional **X-Pro-Gly-containing proteins** such as elastins, prion protein, conotoxins, and **AGO2**. | (pqac-00000001, pqac-00000002, pqac-00000004, pqac-00000006) |
| Complex composition | Active collagen prolyl 4-hydroxylase is an **α2β2 tetramer**. P4HA1 provides the catalytic α subunit, whereas the β subunit is **P4HB/protein disulfide isomerase (PDI)**, which contributes disulfide-isomerase activity, supports complex assembly, and helps retain the enzyme in the ER. | (pqac-00000000, pqac-00000001, pqac-00000003) |
| Subcellular localization | The active enzyme functions in the **lumen of the endoplasmic reticulum (ER)** as part of the early secretory pathway for collagen biosynthesis and maturation. | (pqac-00000000, pqac-00000001, pqac-00000003) |
| Key phenotypes from human genetics | **Biallelic P4HA1 mutations** cause a **congenital connective-tissue disorder** affecting tendon, bone, muscle, and eye; patient fibroblasts show **reduced C-P4H activity**, **reduced proline hydroxylation**, and **decreased collagen thermal stability**. Mouse loss of P4ha1 is embryonic lethal with impaired collagen IV assembly, supporting essential function. | (pqac-00000003, pqac-00000004, pqac-00000007, pqac-00000016) |
| 2023-2024 mechanistic findings | Recent studies/reviews link P4HA1 to **hypoxia/HIF signaling**, tumor ECM remodeling, and metastasis. Reported mechanisms include **HIF-associated upregulation**, **lactate-fueled α-KG supply** that increases P4HA1-dependent collagen hydroxylation in prostate cancer, roles in **EMT/invasion**, links to **chemoresistance/stemness** in some cancers, and a **fibro-inflammatory IL-10/JAK2/STAT3/HIF1α/TMEM45A/P4HA1 axis** in pleural remodeling. | (pqac-00000005, pqac-00000008, pqac-00000009, pqac-00000011, pqac-00000013) |
| Translational applications | P4HA1 is being explored as a **biomarker** of aggressive/hypoxic tumors and fibrosis-related remodeling. Preclinical targeting strategies include **P4HA1 siRNA delivery** and small-molecule inhibition (e.g., **PythiDC/diethyl-pythiDC** in cited literature). Clinically, selective targeting matters because some **HIF-PHD inhibitors** can inhibit collagen prolyl 4-hydroxylation as an **off-target effect**, exemplified by reduced MBL hydroxylation/secretion with **roxadustat** and **vadadustat**. | (pqac-00000002, pqac-00000006, pqac-00000008, pqac-00000010, pqac-00000014) |


*Table: This table summarizes core functional annotation for human P4HA1, including its catalytic role, substrates, cofactors, localization, disease genetics, recent mechanistic findings, and translational relevance. It is useful as a compact evidence-linked reference for narrative reporting.*