SEC15B Antibody

Definition and Target Specificity

The SEC15B antibody is a research reagent designed to detect the SEC15B protein, a component of the exocyst complex (EXOC6B) critical for membrane trafficking and exocytosis. SEC15B is part of a conserved protein family (SEC15/EXOC6) with isoforms specialized for distinct cellular functions across species, including mammals and plants .

Role in STAT3 Exosome Secretion

In mouse embryonic stem cells (mESCs), SEC15B interacts directly with STAT3, facilitating its packaging into multivesicular bodies (MVEs) and secretion via exosomes. This process is regulated by leukemia inhibitory factor (LIF), which induces a "helix-helix interaction" between the N-terminal domains of SEC15B (1–374) and STAT3 (1–355) . Key findings include:

• LIF-Dependent Binding: STAT3 and SEC15B dissociate when LIF is withdrawn but colocalize upon LIF treatment .

• Structural Basis: Mutations in STAT3 (e.g., K117K180R, Y293F) disrupt SEC15B binding, impairing exosome secretion .

• Functional Impact: SEC15B-mediated STAT3 exosome secretion maintains pluripotency in mESCs, with knockdown reducing self-renewal capacity .

Isoform-Specific Functions

In plants, SEC15a and SEC15b isoforms exhibit divergent roles:

• SEC15a: Localizes to pollen tube tips and plasmodesmata, critical for male gametophyte development .

• SEC15b: Dominates in sporophytes, regulating root hair elongation, hypocotyl growth, and seed coat mucilage formation .

• Cross-Talk: SEC15b also supports pollen tube elongation in vitro, despite low expression in pollen, suggesting non-redundant roles .

Western Blotting

• Protocol: Detects endogenous SEC15B in lysates from mESCs, PC12 cells, or plant tissues .

• Controls: Use non-transfected cells or isoform-specific knockouts to validate specificity .

Co-Immunoprecipitation (Co-IP)

• Interactions: Identifies SEC15B complexes with STAT3, Rab GTPases, or other exocyst components (e.g., Sec5, Sec8) .

• Example: LIF-treated mESCs show increased SEC15B-STAT3 co-IP signal compared to untreated cells .

Immunofluorescence (IF)

• Localization: Tracks SEC15B at the plasma membrane in root cells (plants) or MVEs in mESCs .

• Challenges: Requires optimization for membrane-bound protein detection (e.g., permeabilization protocols) .

Cross-Reactivity

• Species Specificity: Confirm reactivity with target species (e.g., Santa Cruz sc-34374 works for human and mouse but not plants) .

• Isoform Discrimination: SEC15a and SEC15b antibodies may not cross-react due to divergent sequences .

Validation

• Positive Controls: Use tissues with high SEC15B expression (e.g., mouse embryonic cells, plant root tips) .

• Negative Controls: Include SEC15B knockout cells or species-specific blocking peptides .