Biology:COL4A3BP

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Short description: Protein-coding gene in the species Homo sapiens


A representation of the 3D structure of the protein myoglobin showing turquoise α-helices.
Generic protein structure example

Collagen type IV alpha-3-binding protein, also known as ceramide transfer protein (CERT) or StAR-related lipid transfer protein 11 (STARD11) is a protein that in humans is encoded by the COL4A3BP gene.[1][2] The protein contains a pleckstrin homology domain at its amino terminus and a START domain towards the end of the molecule. It is a member of the StarD2 subfamily of START domain proteins.

Function and structure

Ceramide transferase protein (or CERT) is responsible for the transfer of ceramide from the endoplasmic reticulum (ER) to the Golgi apparatus. Ceramide plays a very important role in the metabolism and biosynthesis of sphingolipid. More specifically, it is synthesized at the ER, then is transferred by CERT to Golgi where it is converted to sphingomyelin (SM).[3]

There are two pathways through which this transfer takes place: a major pathway, which is ATP and cytosol-dependent and a minor pathway, which is ATP- and cytosol-independent.[2]

CERT is a 68kDa protein[4] that consists of three different parts, each of which with a special role:

  1. Pleckstrin homology domain (PH): It is the aminoterminal domain and it consists of about 100 aminoacid residues.[1][5] The main function of this part of CERT is to recognize and bind various phosphatidyloinositol phosphates (PIPs) with different level of specificity.[6] The isomers of PIPs are distributed to various organelles: PI-4,5-diphosphate goes to the plasma membrane, PI-3-monophosphate to endosomes and PI-4-monophosphate to Golgi.[7] PH domain of wild-type CERT has been found to recognize specifically PI4P and therefore CERT targets the Golgi apparatus or the trans-Golgi network.[4][8][9]
  2. START domain: It consists of about 210 amino acid residues and has an important role in the transfer of ceramide, which is that it can recognize specifically only the natural D-erythro isomer of ceramide and extract it from the membrane.[4]
  3. FFAT motif (two phenylalanines in an acidic tract, that has a conserved sequence "EFFDAxE"): It is a short domain situated between PH and START domain and is the one responsible for the interaction of CERT with ER. More specifically, it binds to the ER resident type II membrane protein, vesicle-associated membrane protein (VAMP) associated protein (VAP), an interaction that is necessary for the transfer of ceramide from the ER to Golgi.[10]

All of these domains are important for the transfer of ceramide, since first of all CERT will extract newly synthesized ceramide from the membrane with the help of its START domain. Then, ceramide will be transferred through the cytosol towards Golgi because of the interaction between the PH domain and PI4P. Finally, interaction with ER is facilitated through the binding of the FFAT motif with vesicle-associated membrane protein.

Regulation

The transport of ceramide by CERT requires ATP.[11] CERT – when expressed in mammalian cells – has been found to receive a lot of possible phosphorylations at the serine repeat (SR) motif, which is close to the PH domain.[12]

It has been shown that the phosphorylation of this SR motif leads to inactivation of the PI4P-binding and ceramide transferring activities of CERT, since it induces an autoinhibitory reaction between the PH and START domains of CERT, transforming it from the active form to the inactive form.[12]

Protein kinase D (PKD) has been found to phosphorylate the SR motif of CERT.[13] Also, CERT is further phosphorylated by the casein kinase 1 family leading to hyperphosphorylation of the SR motif.[14] On the other hand, the integral membrane protein protein phosphatase 2Cε (PP2Cε), which is located on the endoplasmic reticulum induces dephosphorylation of CERT.[15] Dephosphorylated CERT is in the active form in order to be functional and transfer ceramide from ER to Golgi.[16]

Inhibitor HPA-12

The chemically synthesized compound N-(30hydroxy-1-hydroxymethyl-3-phenylpropyl)dodecamide (HPA-12) has been found to be an inhibitor of CERT-mediated ceramide trafficking.[17] More specifically, this drug inhibits the ATP-dependent transport of ceramide from ER to Golgi (and therefore the conversion of ceramide to sphingomyelin), but it does not inhibit protein trafficking. This suggests that Ceramide is still transformed to Glycosylceramide at Golgi. Moreover, it has been shown that it does not inhibit the Sphingomyelin synthase in vitro or in vivo.[17] Moreover, only the (1R, 3R) isomer of HPA-12 has been found to be an active inhibitor[17] and the length of the chain as well as the two hydroxyl-groups are very important for the inhibitory activity.[18]

Clinical significance

This gene encodes a kinase also known as Goodpasture antigen-binding protein that specifically phosphorylates the N-terminal region of the non-collagenous domain of the alpha 3 chain of type IV collagen, known as the Goodpasture antigen. Goodpasture's syndrome is the result of an autoimmune response directed at this antigen. One isoform of this protein is also involved in ceramide intracellular transport. Two transcripts exist for this gene.[2]

Model organisms

Model organisms have been used in the study of COL4A3BP function. A conditional knockout mouse line called Col4a3bptm1a(KOMP)Wtsi was generated at the Wellcome Trust Sanger Institute.[19] Male and female animals underwent a standardized phenotypic screen[20] to determine the effects of deletion.[21][22][23][24] Additional screens performed: In-depth immunological phenotyping[25] – in-depth bone and cartilage phenotyping[26]

References

  1. ↑ 1.0 1.1 "Characterization of a novel type of serine/threonine kinase that specifically phosphorylates the human goodpasture antigen". The Journal of Biological Chemistry 274 (18): 12642–9. Apr 1999. doi:10.1074/jbc.274.18.12642. PMID 10212244. 
  2. ↑ 2.0 2.1 2.2 "Entrez Gene: COL4A3BP collagen, type IV, alpha 3 (Goodpasture antigen) binding protein". https://www.ncbi.nlm.nih.gov/sites/entrez?Db=gene&Cmd=ShowDetailView&TermToSearch=10087. 
  3. ↑ "De novo sphingolipid biosynthesis: a necessary, but dangerous, pathway". The Journal of Biological Chemistry 277 (29): 25843–6. Jul 2002. doi:10.1074/jbc.R200009200. PMID 12011104. 
  4. ↑ 4.0 4.1 4.2 "Molecular machinery for non-vesicular trafficking of ceramide". Nature 426 (6968): 803–9. Dec 2003. doi:10.1038/nature02188. PMID 14685229. Bibcode: 2003Natur.426..803H. 
  5. ↑ "Goodpasture antigen-binding protein, the kinase that phosphorylates the goodpasture antigen, is an alternatively spliced variant implicated in autoimmune pathogenesis". The Journal of Biological Chemistry 275 (51): 40392–9. Dec 2000. doi:10.1074/jbc.M002769200. PMID 11007769. 
  6. ↑ "Signal-dependent membrane targeting by pleckstrin homology (PH) domains". The Biochemical Journal 350 (1): 1–18. Aug 2000. doi:10.1042/0264-6021:3500001. PMID 10926821. 
  7. ↑ "Phosphoinositides and the golgi complex". Current Opinion in Cell Biology 14 (4): 434–47. Aug 2002. doi:10.1016/S0955-0674(02)00357-5. PMID 12383794. 
  8. ↑ "Targeting of Golgi-specific pleckstrin homology domains involves both PtdIns 4-kinase-dependent and -independent components". Current Biology 12 (9): 695–704. Apr 2002. doi:10.1016/S0960-9822(02)00779-0. PMID 12007412. 
  9. ↑ "Phosphatidylinositol 4 phosphate regulates targeting of clathrin adaptor AP-1 complexes to the Golgi". Cell 114 (3): 299–310. Aug 2003. doi:10.1016/S0092-8674(03)00603-2. PMID 12914695. 
  10. ↑ "A conserved ER targeting motif in three families of lipid binding proteins and in Opi1p binds VAP". The EMBO Journal 22 (9): 2025–35. May 2003. doi:10.1093/emboj/cdg201. PMID 12727870. 
  11. ↑ "Reconstitution of ATP- and cytosol-dependent transport of de novo synthesized ceramide to the site of sphingomyelin synthesis in semi-intact cells". The Journal of Biological Chemistry 275 (39): 29938–45. Sep 2000. doi:10.1074/jbc.M004470200. PMID 10882735. 
  12. ↑ 12.0 12.1 "Interorganelle trafficking of ceramide is regulated by phosphorylation-dependent cooperativity between the PH and START domains of CERT". The Journal of Biological Chemistry 282 (24): 17758–66. Jun 2007. doi:10.1074/jbc.M702291200. PMID 17442665. 
  13. ↑ "Regulation of secretory transport by protein kinase D-mediated phosphorylation of the ceramide transfer protein". The Journal of Cell Biology 178 (1): 15–22. Jul 2007. doi:10.1083/jcb.200612017. PMID 17591919. 
  14. ↑ "Casein kinase I{gamma}2 down-regulates trafficking of ceramide in the synthesis of sphingomyelin". Molecular Biology of the Cell 20 (1): 348–57. Jan 2009. doi:10.1091/mbc.E08-07-0669. PMID 19005213. 
  15. ↑ "Protein phosphatase 2Cepsilon is an endoplasmic reticulum integral membrane protein that dephosphorylates the ceramide transport protein CERT to enhance its association with organelle membranes". The Journal of Biological Chemistry 283 (10): 6584–93. Mar 2008. doi:10.1074/jbc.M707691200. PMID 18165232. 
  16. ↑ "Intracellular trafficking of ceramide by ceramide transfer protein". Proceedings of the Japan Academy, Series B 86 (4): 426–37. 2010. doi:10.2183/pjab.86.426. PMID 20431265. Bibcode: 2010PJAB...86..426H. 
  17. ↑ 17.0 17.1 17.2 "CERT mediates intermembrane transfer of various molecular species of ceramides". The Journal of Biological Chemistry 280 (8): 6488–95. Feb 2005. doi:10.1074/jbc.M409290200. PMID 15596449. 
  18. ↑ "Stereoselective synthesis and structure-activity relationship of novel ceramide trafficking inhibitors. (1R,3R)-N-(3-hydroxy-1-hydroxymethyl-3-phenylpropyl)dodecanamide and its analogues". Journal of Medicinal Chemistry 46 (17): 3688–95. Aug 2003. doi:10.1021/jm0300779. PMID 12904073. 
  19. ↑ Gerdin AK (2010). "The Sanger Mouse Genetics Programme: high throughput characterisation of knockout mice". Acta Ophthalmologica 88: 925–7. doi:10.1111/j.1755-3768.2010.4142.x. 
  20. ↑ 20.0 20.1 "International Mouse Phenotyping Consortium". http://www.mousephenotype.org/data/search?q=Col4a3bp#fq=*:*&facet=gene. 
  21. ↑ "A conditional knockout resource for the genome-wide study of mouse gene function". Nature 474 (7351): 337–42. Jun 2011. doi:10.1038/nature10163. PMID 21677750. 
  22. ↑ "Mouse library set to be knockout". Nature 474 (7351): 262–3. Jun 2011. doi:10.1038/474262a. PMID 21677718. 
  23. ↑ "A mouse for all reasons". Cell 128 (1): 9–13. Jan 2007. doi:10.1016/j.cell.2006.12.018. PMID 17218247. 
  24. ↑ "Genome-wide generation and systematic phenotyping of knockout mice reveals new roles for many genes". Cell 154 (2): 452–64. 2013. doi:10.1016/j.cell.2013.06.022. PMID 23870131. 
  25. ↑ 25.0 25.1 "Infection and Immunity Immunophenotyping (3i) Consortium". http://www.immunophenotyping.org/data/search?keys=Col4a3bp&field_gene_construct_tid=All. 
  26. ↑ 26.0 26.1 "OBCD Consortium". http://www.boneandcartilage.com/. 

Further reading

External links




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