| Category | Summary |
|---|---|
| Identity | • **ETR1 / AtETR1 / ETHYLENE RESPONSE 1** from **Arabidopsis thaliana**; UniProt **P49333** matches the canonical Arabidopsis ethylene receptor studied in the cited literature • Type-I ethylene receptor; negative regulator of ethylene signaling (pqac-00000002, pqac-00000011, pqac-00000013) |
| Domains | • N-terminal **transmembrane ethylene-binding domain** (3 TM segments in classic descriptions; some excerpts note 3–4 TM helices) • Followed by **GAF/GAF-like** region • C-terminal **histidine-kinase-like transmitter domain** plus **receiver domain** • Domain architecture aligns with UniProt family/domain assignment and two-component-like receptor models (pqac-00000002, pqac-00000005, pqac-00000013, pqac-00000015) |
| Localization | • Integral membrane receptor localized mainly to the **endoplasmic reticulum (ER)** / ER-associated endomembrane system rather than the plasma membrane • Functions at the ER with downstream components such as CTR1 and EIN2 (pqac-00000011, pqac-00000013) |
| Ligand/cofactor binding | • Binds the gaseous hormone **ethylene** with very high affinity • Requires **Cu(I)** cofactor for ethylene binding • Key residues implicated in binding/mechanism include **Asp25, Cys65, His69, Lys91** • Older model: **1 Cu per receptor dimer**; newer evidence supports **1 Cu per ETR1 monomer** (thus potentially 2 Cu / 2 ethylene-binding sites per dimer) • RAN1 copper transporter is implicated in receptor copper loading/biogenesis (pqac-00000002, pqac-00000003, pqac-00000010, pqac-00000012, pqac-00000014, pqac-00000016) |
| Signaling mechanism | • In air/no ethylene, ETR1 is **active** and represses ethylene responses by promoting **CTR1** activity • Ethylene binding **inactivates/represses receptor output**, leading to CTR1 inactivation, reduced EIN2 phosphorylation, and downstream signal propagation • ETR1 therefore acts as a **negative regulator** at the top of the pathway (pqac-00000002, pqac-00000010, pqac-00000011, pqac-00000012) |
| Protein interactions | • Direct/functional interaction with **CTR1** is central to pathway output • Receptor family forms **dimers/oligomers**; homo- and heteromeric receptor complexes are reported • Interaction/connectivity with **EIN2** is part of current pathway models; receptor-associated complexes help regulate signal transfer (pqac-00000005, pqac-00000006, pqac-00000014) |
| Enzymatic/kinase activity | • ETR1 contains a functional **histidine kinase** region in biochemical assays • Autophosphorylation depends on **His353** and catalytic residues in the kinase domain • Phosphorylation chemistry is consistent with histidyl phosphorylation; **Mn2+** is required for autophosphorylation in the cited assay • However, later genetic work indicates canonical transmitter-domain histidine kinase activity is **not strictly required** for ethylene signal transmission (pqac-00000015, pqac-00000007, pqac-00000011) |
| Quantitative data | • Ethylene sensitivity: **responds to <1 part per billion** ethylene (pqac-00000002) • Ethylene dissociation half-life: **≥12.5 h** (pqac-00000012) • Ethylene activity threshold: **0.2 nl L^-1** (reported in excerpt) (pqac-00000008) • Ethylene production can reach **500 nl g^-1 h^-1** (reported in excerpt) (pqac-00000008) • Copper stoichiometry: older literature/reviews cite **1 Cu per dimer**; recent work supports **1 Cu per monomer** (pqac-00000012, pqac-00000003) • Autophosphorylation cation requirement: **Mn2+** (pqac-00000015) • Explicit equilibrium Kd values for ethylene/copper: **not specified in excerpt** (pqac-00000001, pqac-00000003) |
| Recent 2023-2024 advances | • **2023 PNAS** study refined the high-affinity binding model, emphasizing **Asp25** as critical for high-affinity binding/signaling coupling and supporting a **CH** rather than direct **DCH** copper coordination model • **2023** work linked ethylene signaling dynamics to **CTR1 subcellular trafficking**, with receptor state affecting CTR1 movement and signaling output • **2024** crystallization screening reported ETR1 TM-containing constructs crystallized under many conditions, but high-resolution receptor structure remains unsolved • Figure-based recent structural evidence highlights Asp25-Cys65-His69-Lys91 relationships (pqac-00000001, pqac-00000003, pqac-00000016, pqac-00000017) |
| Applications | • ETR1 biology underpins practical manipulation of **ethylene perception** in agriculture, especially ripening/senescence control • Knowledge of receptor binding informs use of **ethylene antagonists such as 1-MCP** and broader strategies to extend postharvest shelf life • The 2023 structural work explicitly notes relevance to development of **ethylene nanosensors** for agricultural/industrial applications (pqac-00000002, pqac-00000003) |


*Table: This table summarizes the core functional annotation of Arabidopsis thaliana ETR1 (UniProt P49333), including mechanism, localization, ligand/cofactor dependence, quantitative data, and recent advances. It is useful as a compact evidence-linked reference for interpreting ETR1 function in ethylene signaling.*