Sec24B

Sec24B is a protein subunit of the COPII coat complex that drives vesicle formation from the endoplasmic reticulum to the Golgi apparatus. In humans it is encoded by the SEC24B gene. Sec24B is one of four vertebrate Sec24 paralogs (Sec24A, Sec24B, Sec24C, and Sec24D) that confer cargo-selective properties to COPII vesicles. It functions as part of the inner COPII coat, partnering with Sec23 to select cargo and interface with the Sec13/Sec31 outer coat during vesicle budding at ER exit sites.

Cargo selection by Sec24B involves recognition of specific sorting signals on cargo proteins, including di-acidic (DxE) motifs, and contributes to whether particular proteins are included in transport vesicles. The presence of multiple Sec24 isoforms allows cells to tailor cargo profiles for different tissues and developmental stages, enabling nuanced control of ER-to-Golgi trafficking.

Biological and clinical relevance: Proper Sec24B function is essential for efficient ER-to-Golgi transport. Disruption of SEC24B expression or cargo-binding properties can perturb trafficking of certain proteins and has been associated with neural tube defects in some model systems, underscoring its role in development. In experimental models, altering Sec24B activity can affect secretory pathway efficiency and organismal phenotypes, reflecting its integral role in vesicle formation and cargo selection.

Overall, Sec24B is a key cargo adaptor subunit within the COPII system, contributing to the fidelity and specificity of protein export from the ER.