VAPA

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External IDs	GeneCards: [1]
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Species	Human	Mouse
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View/Edit Human

VAMP-Associated Protein A ( or Vesicle-Associated Membrane Protein-Associated Protein A) is a protein that in humans is encoded by the VAPA gene. Together with VAPB and VAPC it forms the VAP protein family. They are integral endoplasmic reticulum membrane proteins of the type II and are ubiquitous among eukaryotes.

VAPA is ubiquitously expressed in human tissues and is thought to be involved in membrane trafficking by interaction with SNAREs. in regulation of lipid transport and metabolism, and in the Unfolded Protein Response (UPR).

Protein structure

The protein is divided in three different domains. First, an N-terminal beta-sheet with an immunoglobulin-like fold that shares homology with the Nematode major sperm protein (MSP). Secondly, a central coiled-coil domain. Then finally a C-terminal transmembrane domain (TMD) which is usually present in proteins of the t-SNARE superfamily and has been found in other proteins associated with vesicular transport. VAPA can form homo-dimers and also hetero dimers with VAPB by interactions through their (TMD).

Intracellular Localisation

Because of its ubiquitous expression, the intracellular localisation and function of VAPA may vary between cell types. It is however mainly located in the ER, Golgi apparatus and the Vesicular Tubular Compartment or ER-Golgi Intermediate Compartment, an organelle of eukaryotic cells consisting in fused ER-derived vesicles that transports proteins from the ER to the Golgi apparatus.

Interactions

VAPA has been documented to interact with three different groups of proteins: proteins associated with vesicle traffic and fusion, proteins containing the FFAT motif and viral proteins.

Vesicle traffic and fusion

VAPA is able to bind a range of SNARE proteins including syntaxin1A, rbet1 and rsec22. It also binds to proteins associated with membrane fusion machinery such as alphaSNAP and NSF.These interaction suggest that VAPA could have a general role in the regulation of the function of these proteins that are mainly involved in membrane fusion

Viral Proteins

VAP proteins have been found to be essential host factors for several viruses.

VAP proteins binds with non-structural proteins of the hepatitis C virus NS5A and NS5B allowing the RNA replication machinery of the virus to set up on the lipid raft membrane of the host cell.

VAPA also binds to several viral proteins from the Norovirus family and is important for the virus replication efficiency. The non-structural proteins NS1 and NS2 are able to bind VAPA thanks to sequence mimicry of the FFAT motif probably yielding the same advantage to viral replication as for hepatitis C virus.

FFAT motif

The N-terminal MSP-homologous part of VAPA is able to bind to the FFAT motif, a particular sequence motif shared by several lipid binding proteins including oxysterol-binding protein (OSBP).

Function

One of its proposed functions is to slow down the lipid flow back towards the ER when protein misfolding occurs, in order to reduce the amount of stress triggered by the UPR. The VAP would regulate this process by inhibiting membrane contact.

Associated Diseases

 The P56S SNP in the MSP domain of VAPB is involved in the onset of Lou Gehrig's disease also called amyotrophic lateral sclerosis (ALS) where the patient loses muscle control and function. The degenerescence of motor neurons observed in such condition could to be due to the inability of VAPB to regulate the lipid function around the ER and the subsequent consequences on cell function.

Further reading

• Lapierre LA, Tuma PL, Navarre J, Goldenring JR, Anderson JM (November 1999). "VAP-33 localizes to both an intracellular vesicle population and with occludin at the tight junction". Journal of Cell Science. 112 ( Pt 21) (21): 3723–32. PMID 10523508.
• Tu H, Gao L, Shi ST, Taylor DR, Yang T, Mircheff AK, Wen Y, Gorbalenya AE, Hwang SB, Lai MM (October 1999). "Hepatitis C virus RNA polymerase and NS5A complex with a SNARE-like protein". Virology. 263 (1): 30–41. doi:10.1006/viro.1999.9893. PMID 10544080.
• Weir ML, Xie H, Klip A, Trimble WS (August 2001). "VAP-A binds promiscuously to both v- and tSNAREs". Biochemical and Biophysical Research Communications. 286 (3): 616–21. doi:10.1006/bbrc.2001.5437. PMID 11511104.
• Wyles JP, McMaster CR, Ridgway ND (August 2002). "Vesicle-associated membrane protein-associated protein-A (VAP-A) interacts with the oxysterol-binding protein to modify export from the endoplasmic reticulum". The Journal of Biological Chemistry. 277 (33): 29908–18. doi:10.1074/jbc.M201191200. PMID 12023275.
• Matsuda A, Suzuki Y, Honda G, Muramatsu S, Matsuzaki O, Nagano Y, Doi T, Shimotohno K, Harada T, Nishida E, Hayashi H, Sugano S (May 2003). "Large-scale identification and characterization of human genes that activate NF-kappaB and MAPK signaling pathways". Oncogene. 22 (21): 3307–18. doi:10.1038/sj.onc.1206406. PMID 12761501.
• Gao L, Aizaki H, He JW, Lai MM (April 2004). "Interactions between viral nonstructural proteins and host protein hVAP-33 mediate the formation of hepatitis C virus RNA replication complex on lipid raft". Journal of Virology. 78 (7): 3480–8. doi:10.1128/JVI.78.7.3480-3488.2004. PMC 371042. PMID 15016871.
• Evans MJ, Rice CM, Goff SP (August 2004). "Phosphorylation of hepatitis C virus nonstructural protein 5A modulates its protein interactions and viral RNA replication". Proceedings of the National Academy of Sciences of the United States of America. 101 (35): 13038–43. Bibcode:2004PNAS..10113038E. doi:10.1073/pnas.0405152101. PMC 516513. PMID 15326295.
• Suzuki Y, Yamashita R, Shirota M, Sakakibara Y, Chiba J, Mizushima-Sugano J, Nakai K, Sugano S (September 2004). "Sequence comparison of human and mouse genes reveals a homologous block structure in the promoter regions". Genome Research. 14 (9): 1711–8. doi:10.1101/gr.2435604. PMC 515316. PMID 15342556.
• Rual JF, Venkatesan K, Hao T, Hirozane-Kishikawa T, Dricot A, Li N, Berriz GF, Gibbons FD, Dreze M, Ayivi-Guedehoussou N, Klitgord N, Simon C, Boxem M, Milstein S, Rosenberg J, Goldberg DS, Zhang LV, Wong SL, Franklin G, Li S, Albala JS, Lim J, Fraughton C, Llamosas E, Cevik S, Bex C, Lamesch P, Sikorski RS, Vandenhaute J, Zoghbi HY, Smolyar A, Bosak S, Sequerra R, Doucette-Stamm L, Cusick ME, Hill DE, Roth FP, Vidal M (October 2005). "Towards a proteome-scale map of the human protein-protein interaction network". Nature. 437 (7062): 1173–8. Bibcode:2005Natur.437.1173R. doi:10.1038/nature04209. PMID 16189514.
• Hamamoto I, Nishimura Y, Okamoto T, Aizaki H, Liu M, Mori Y, Abe T, Suzuki T, Lai MM, Miyamura T, Moriishi K, Matsuura Y (November 2005). "Human VAP-B is involved in hepatitis C virus replication through interaction with NS5A and NS5B". Journal of Virology. 79 (21): 13473–82. doi:10.1128/JVI.79.21.13473-13482.2005. PMC 1262604. PMID 16227268.
• Kawano M, Kumagai K, Nishijima M, Hanada K (October 2006). "Efficient trafficking of ceramide from the endoplasmic reticulum to the Golgi apparatus requires a VAMP-associated protein-interacting FFAT motif of CERT". The Journal of Biological Chemistry. 281 (40): 30279–88. doi:10.1074/jbc.M605032200. PMID 16895911.