The VAP protein family (Vesicle‑Associated Membrane Protein‑Associated Protein) comprises a group of integral endoplasmic‑reticulum (ER) membrane proteins that are conserved across eukaryotes. The most widely studied members in mammals are VAPA (VAP‑A) and VAPB (VAP‑B).
Key characteristics
| Feature | Details |
|---|---|
| Domain architecture | An N‑terminal major sperm protein (MSP) – like domain that projects into the cytosol, a coiled‑coil region, and a C‑terminal transmembrane helix that anchors the protein in the ER membrane. |
| Cellular location | Primarily the ER membrane; VAP proteins can also be found at membrane contact sites where the ER interfaces with other organelles (e.g., plasma membrane, Golgi, mitochondria, endosomes). |
| Primary functions | • Mediate lipid transfer and membrane tethering through interaction with FFAT‑motif‑containing proteins (two phenylalanines in an acidic tract). • Participate in ER‑Golgi transport, unfolded protein response, and regulation of lipid metabolism. |
| Interaction partners | Proteins bearing FFAT motifs such as OSBP (oxysterol‑binding protein), CERT (ceramide transfer protein), and several tethering factors. |
| Physiological relevance | • Essential for proper ER morphology and organelle communication. • Involved in secretion, lipoprotein production, and calcium homeostasis. |
| Disease associations | Mutations in VAPB (e.g., P56S) are linked to familial forms of amyotrophic lateral sclerosis (ALS) and spinal muscular atrophy–linked motor neuron disease. Aberrant VAP function has also been implicated in viral infection cycles (e.g., hepatitis C virus replication). |
Evolutionary conservation
VAP homologs are present in yeast (Scs2, Scs22), plants (VAP27‑1, VAP27‑2), and diverse metazoans, indicating an ancient and conserved role in membrane organization.
Research relevance
The MSP‑like domain of VAP proteins serves as a model for studying protein–protein interactions mediated by the FFAT motif. Structural studies (X‑ray crystallography, NMR) have resolved the MSP domain, facilitating drug‑design efforts targeting VAP‑mediated pathways in neurodegeneration and viral replication.
