| Domain/Region | Amino Acid Residues | Structural Features | Key Functions | Key Interacting Partners |
|---|---:|---|---|---|
| N-terminal dimerization domain | 1-69 | Homodimeric four-helix bundle per protomer; forms a tight hydrophobic dimer core; presents a negatively charged surface that binds a single UBL domain and breaks dimer symmetry; connected to the TPR domain by a flexible linker (~14 aa) (pqac-00000016, pqac-00000017) | Mediates SGTA homodimerization; recruits SGTA into TA-targeting and quality-control assemblies; enables binding to UBL-containing BAG6-pathway factors and helps organize substrate handoff during triage (pqac-00000016, pqac-00000002, pqac-00000008) | UBL4A/Get5, BAG6 UBL domain, BAG6 complex/TRC35-UBL4A-BAG6 (pqac-00000016, pqac-00000002, pqac-00000008) |
| TPR domain | 86-208 | Three TPR motifs plus a capping helix; right-handed superhelical fold; CC-TPR/carboxylate-clamp architecture that recognizes C-terminal EEVD motifs of cytosolic Hsp70/Hsp90 family chaperones (pqac-00000016, pqac-00000005, pqac-00000018) | Couples SGTA to the cytosolic chaperone network; supports Hsp70-assisted loading of hydrophobic clients, including tail-anchored proteins; also links SGTA to broader proteostasis pathways including proteasomal regulation (pqac-00000018, pqac-00000006, pqac-00000002) | Hsp70/Hsc70, Hsp90, proteasomal ADRM1/Rpn13; more broadly EEVD-bearing cytosolic chaperones (pqac-00000002, pqac-00000005, pqac-00000018) |
| C-terminal substrate-binding domain / glutamine-rich region | 211-313; glutamine-rich segment ~274-313 | Flexible, methionine-rich client-binding region with conserved glutamine-rich/NNP-repeat features in metazoans; structural modeling supports a "helical-hand" hydrophobic groove that binds a short hydrophobic helix, with preference for clients having a hydrophobic face and a minimal helix length of ~11 residues (pqac-00000016, pqac-00000018) | Directly binds hydrophobic transmembrane segments of tail-anchored proteins and mislocalized membrane proteins; shields exposed hydrophobicity in the cytosol; helps determine triage between productive ER targeting and BAG6-dependent quality control/degradation (pqac-00000017, pqac-00000018, pqac-00000002, pqac-00000011) | Tail-anchored membrane proteins, mislocalized membrane proteins, hydrophobic client TMDs including SGTA-associated cargos such as syntaxin-5 and MAVS in cell-based studies (pqac-00000018, pqac-00000012, pqac-00000002) |


*Table: This table summarizes the major structural regions of human SGTA, their residue ranges, molecular features, and experimentally supported functions and partners. It is useful for connecting SGTA domain architecture to its roles in tail-anchored protein targeting and cytosolic protein quality control.*