• Purity

  >95%, by SDS-PAGE under reducing conditions and visualized by silver stain

• Endotoxin Level

  <0.10 EU per 1 μg of the protein by the LAL method.  

• Activity

  Measured by its binding ability in a functional ELISA. When rmEphB2/Fc Chimera (Catalog # 467-B2) is coated at 2 μg/mL (100 μL/well), the concentration of rhVAP-A that produces 50% of the optimal binding response is found to be approximately 0.8‑4 μg/mL.

• Source

  E. coli-derived Met1-Met132, with a C-terminal 6-His tag

• Accession #

• N-terminal Sequence    
  Analysis

  Ala2

• Structure / Form

  Monomer

• Predicted Molecular Mass

  15.5 kDa

• SDS-PAGE

  16 kDa, reducing conditions

Background: VAP-A

Vesicle-associated membrane protein (VAMP)‑associated protein A (VAP‑A; also VAMP‑A and VAP-33) is a 33 kDa, ubiquitously expressed, type IV transmembrane protein belonging to the VAP family of proteins (1). It is found in plasma and ER membranes as well as in intracellular vesicles as a homodimer and a heterodimer with VAP-B. Human VAP-A is synthesized as a 249 amino acid (aa) precursor that contains a 227 aa cytoplasmic domain and a 21 aa transmembrane region. The cytoplasmic domain contains a mobile sperm protein (MSP) domain (aa 14 ‑ 131) and a coiled-coil region (aa 169 ‑ 205). Human VAP-A is 97% aa identical to mouse and rat VAP-A. VAP-A and VAP-B recruit FFAT (two phenylalanines in an acidic tract)-motif-containing proteins to the cytosolic surface of ER membranes through a conserved region within their MSP domain, and they have been implicated in regulation of membrane transport, phospholipid biosynthesis, and the unfolded protein response (2 ‑ 3). Their role in maintaining the identities of intracellular organelles has not been demonstrated, but their ability to interact with lipid-transfer/binding proteins (LT/BPs) may affect the lipid composition of certain cellular membranes (2, 4). One study shows that VAPs play a critical role in maintaining the structural and functional properties of the Golgi complex (2). Researchers found that knockdown of VAP reduces the levels of phosphatidylinositol-4-phosphate (PI4P), diacylglycerol (DAG), and sphingomyelin (SM) in Golgi membranes and exports pleiotropic effects in Golgi-mediated transport (2). The effects of VAPs are mediated by their interacting FFAT-motif-containing proteins Nir2, OSBP, and CERT (2). VAPs provide a scaffold for these LT/BPs at the ER-Golgi membrane contact sites, thereby affecting the lipid composition of the Golgi membranes and consequently their structural and functional identities (2). Most recently, researchers found that VAP-A associates and co‑localizes with protrudin, a protein that promotes neurite formation, and found that it was an important regulator both of the subcellular localization of protrudin and of its ability to stimulate neurite outgrowth (5).

• References:

1. Weir, M.L. et al. (1998) Biochem. J. 333:247.

2. Peretti, D. et al. (2008) Mol. Biol. Cell 19:3871.

3. Kaiser, S.E. et al. (2005) Structure 13:1035.

4. Loewen, C.J. et al. (2003) EMBO J. 22:2025.

5. Saita, S. et al. (2009) J. Biol. Chem. 284:13766.

• Long Name:

  VAMP [Vesicle-associated Membrane Protein]-associated Protein A

• Entrez Gene IDs:

  9218 (Human); 30960 (Mouse); 58857 (Rat)

• Alternate Names:

  hVAP-33; MGC3745,33 kDa VAMP-associated protein; VAMP (vesicle-associated membrane protein)-associated protein A, 33kDa; VAMP-A; VAP-33; VAP33VAMP (vesicle-associated membrane protein)-associated protein A (33kD); VAPA; VAP-A; VAP-AVAMP-associated protein A; vesicle-associated membrane protein-associated protein A