| Domain Name | Location/Region | Key Residues | Function | Supporting Evidence/Citations |
|---|---|---|---|---|
| Regulatory region | N-terminal half of PKCδ; separated from catalytic region by V3 hinge | Includes pseudosubstrate plus C1 and C2-like modules | Autoinhibits the kinase in the basal state, mediates lipid sensing, and helps control subcellular targeting and activation state | PKC family members share an N-terminal regulatory moiety linked to a conserved C-terminal kinase domain; PKCδ specifically contains regulatory and catalytic regions separated by V3 (pqac-00000007, pqac-00000008) |
| Pseudosubstrate segment | N-terminus within regulatory region, upstream of C1 domains | Autoinhibitory pseudosubstrate sequence; specific residue motif not detailed in retrieved texts | Maintains basal autoinhibition until maturation/phosphorylation and membrane-dependent activation relieve inhibition | PKC architecture includes an autoinhibitory pseudosubstrate preceding the C1 domain; PKC activation involves exposure/release of the pseudosubstrate (pqac-00000007, pqac-00000008) |
| C1 domain (overall) | Regulatory region; tandem cysteine-rich lipid-binding module | Conserved cysteine-rich motifs; DAG-binding groove; Trp252 highlighted in PKCδ C1B structural analysis | Binds DAG and phosphatidylserine/phorbol esters, enabling membrane recruitment and activation in response to phospholipase C-generated lipids | PKCδ is a novel PKC activated by DAG and PS but not Ca2+; the C1 region binds DAG/PS and contains tandem Cys-rich motifs (pqac-00000004, pqac-00000008) |
| C1A/C1B subdomains | Within C1 tandem repeat | C1A and C1B non-equivalent; C1B is major PS-binding site; Trp252 associated with DAG interaction/toggling | Provide isoform-specific lipid sensing; C1B is the principal membrane lipid/phorbol-ester interacting module in PKCδ | PKCδ C1A and C1B are not equivalent, with C1B as the major PS-binding site; crystal structures of PKCδ C1B show stereospecific DAG binding and identify Trp252 as important for DAG-related behavior (pqac-00000008, pqac-00000003) |
| C2-like domain | Amino-terminal regulatory region, adjacent to C1 | Lacks key Ca2+-coordinating residues present in conventional PKC C2 domains | Distinguishes PKCδ from conventional PKCs; does not confer classical Ca2+-dependent membrane targeting | PKCδ lacks an authentic Ca2+-binding C2 domain and instead has a C2-like region missing residues needed for Ca2+ coordination (pqac-00000008, pqac-00000004) |
| C3 domain | N-lobe of catalytic/kinase core in C-terminal half | ATP-binding site | Binds ATP for phosphotransfer during serine/threonine kinase catalysis | The C3 and C4 domains form the kinase core, with C3 corresponding to the ATP-binding lobe/site; PKCδ drug targeting often focuses on the ATP-binding site in the catalytic domain (pqac-00000007, pqac-00000008) |
| C4 domain | C-terminal catalytic core | Activation-loop Thr505; substrate-recognition region | Contains substrate-binding determinants and catalytic elements required for phosphotransfer to protein substrates | Retrieved reviews state that the C4 region contains the substrate-binding region and harbors the activation-loop phosphorylation site Thr505 (pqac-00000008, pqac-00000004) |
| Catalytic region | C-terminal half of PKCδ, downstream of V3 hinge | C3/C4 kinase core; phospho-acceptor regulatory sites T505, S643, S662 | Executes serine/threonine phosphorylation of substrates after activation; also contains major sites for maturation/priming phosphorylation | PKCδ catalytic domain binds ATP/GTP and protein substrates; catalytic activation depends on conserved phosphosites in activation loop, turn motif, and hydrophobic motif (pqac-00000008, pqac-00000007) |
| Activation-loop phosphosite | C4 activation loop | Thr505 (T505) | Required for catalytic competence and part of the ordered maturation/activation process; also elevated in stress signaling | Reviews identify Thr505 as the activation-loop site; neuronal stress study reports PKCδ phosphorylation at T505 accompanying activation (pqac-00000008, pqac-00000011) |
| Turn motif phosphosite | Carboxyl-terminal catalytic tail/hinge-associated motif | Ser643 (S643) | Contributes to PKCδ maturation, stability, and maintenance of an active-competent conformation | PKCδ contains a conserved hinge/turn motif phosphorylation site at Ser643; PKC maturation involves ordered phosphorylation including turn motif phosphorylation (pqac-00000008, pqac-00000007) |
| Hydrophobic motif phosphosite | Carboxyl-terminal tail | Ser662 (S662) | Supports maturation/stability and full catalytic competence of PKCδ | PKCδ contains a conserved hydrophobic motif phosphorylation site at Ser662; hydrophobic motif phosphorylation is part of PKC maturation (pqac-00000008, pqac-00000007) |
| Nuclear localization signal (NLS) | Present in full-length PKCδ/catalytic fragment; functionally exposed after proteolytic activation | Specific sequence not provided in retrieved texts | Enables nuclear translocation of the active catalytic fragment, allowing phosphorylation of nuclear substrates and regulation of apoptosis-related transcriptional programs | Activated PKCδ is cleaved by caspase-3 into a constitutively active ~40/41-kDa catalytic fragment that translocates to the nucleus via its NLS; nuclear localization is required for Lamin B1 phosphorylation in neuronal stress models (pqac-00000006, pqac-00000011) |
| Caspase-3 cleavage site / proteolytic activation module | Hinge region between regulatory and catalytic halves | Exact cleavage residue not specified in retrieved texts; cleavage generates ~40/41-kDa catalytic fragment and ~38-kDa regulatory fragment | Converts PKCδ into a constitutively active catalytic fragment during apoptotic/oxidative stress signaling | Multiple sources report caspase-3-dependent cleavage of native PKCδ (72–74 kDa) into an active catalytic fragment and regulatory fragment, a hallmark of PKCδ activation in stress/apoptosis pathways (pqac-00000006, pqac-00000011) |


*Table: This table summarizes the major structural and regulatory features of PKCδ relevant to annotating Xenopus tropicalis LOC101732819 as a PRKCD ortholog. It emphasizes domain architecture, lipid sensing, catalytic regulation, and the key activation features most useful for functional annotation.*