Sandbox Reserved 313: Difference between revisions
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''Secretory sphingomyelinase (sSMase)'' - | ''Secretory sphingomyelinase (sSMase)'' - | ||
''Neutral Mg2+-dependent sphingomyelinases (nSMase)'' - | ''Neutral Mg2+-dependent sphingomyelinases (nSMase)'' - The membrane bound dependent nSMase has an neatral pH optimum and is found predominantly in the brain. This neutral SMase enzyme relies on Magnesium and is activated by unsaturated fatty acids and phosphatidylserine<ref name="gp6">PMID: 10713073 </ref>. | ||
''Neutral Mg2+-independent sphingomyelinases'' - | ''Neutral Mg2+-independent sphingomyelinases'' - | ||
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=Structure and Function= | =Structure and Function= | ||
Recently, in the 1980's, the primary structure of sphingomyelinase was determined by cloning the first N-SMases from ''Bacillus cereus'' and ''Staphylococcus aureus'' and by the subsequent sequencing of their cDNAs <ref name=" | Recently, in the 1980's, the primary structure of sphingomyelinase was determined by cloning the first N-SMases from ''Bacillus cereus'' and ''Staphylococcus aureus'' and by the subsequent sequencing of their cDNAs <ref name="gp7">PMID: 2127932 </ref>. | ||
The crystal structure of sphingomyelinase has been solved using the bacterium ''Listeria ivanovii'' and ''Bacillus cereus(Bc-SMase)'' to gain further insight into its catalytic activities <ref name=" | The crystal structure of sphingomyelinase has been solved using the bacterium ''Listeria ivanovii'' and ''Bacillus cereus(Bc-SMase)'' to gain further insight into its catalytic activities <ref name="gp6">PMID: 16595670 </ref>. The overall structure of Bc-SMase has been determined to consist of a β-sandwich with α/β motifs<ref name="gp">PMID: 16595670 </ref>. Through SMase structure identification, it has been determined to be a member of the DNA I-like superfamily having geometrically identical amino acid residues as the enzymes in this superfamily. The only different with SMase, is that it has a unique hydrophobic beta-hairpin structure. The crystal structure revealed that this unique beta-hairpin region has two solvent exposed aromatic amino acids on the top which bind to the cell surfaces to catalyze hemolysis. | ||
=Mechanism= | =Mechanism= | ||
It has been proposed that the mechanism of Bc-SMase is similar to that of bovine pancreatic DNase 1 because Bc-SMase and bovine DNase 1 are homologous proteins which both have conserved alleged catalytic amino acid residues and a similar molecular structure<ref name=" | It has been proposed that the mechanism of Bc-SMase is similar to that of bovine pancreatic DNase 1 because Bc-SMase and bovine DNase 1 are homologous proteins which both have conserved alleged catalytic amino acid residues and a similar molecular structure<ref name="gp7">PMID: 16595670 </ref>. . The proposed hydrolytic activity of Bc-SMAse cloned from ''Bacillus cereus'' is coordinated by essential water bridged divalent metal ions. Two metal ions which are bound to the Glu-53 and <scene name='Sandbox_Reserved_313/His-296/2'>His-296</scene> residues in the central cleft which orientate the substrate in the active site. The divalent cation which is linked to His-296 provides a general base water and a phosphate from sphingomelin binds to the central cleft at the site of the water bridged double metal ions. The divalent metal ion which is located at Glu-53 then binds to sphingomelin by directly interacting with the amide oxygen and the O-4 ester oxygen. | ||
=Implications= | =Implications= | ||
The crystal structure of Bc-SMase has some significant implications for unlocking the poorly characterized structure of neutral sphingomyelinase (nSMase) found in mammals. Bc-SMase is a homologue of nSMase, sharing similar metal ion dependence, amino acid sequence identity, and a similar hydrolytic mechanism<ref name="gp">PMID: 16595670 </ref>. | The crystal structure of Bc-SMase has some significant implications for unlocking the poorly characterized structure of neutral sphingomyelinase (nSMase) found in mammals. Bc-SMase is a homologue of nSMase, sharing similar metal ion dependence, amino acid sequence identity, and a similar hydrolytic mechanism<ref name="gp">PMID: 16595670 </ref>. | ||
=References= | =References= | ||
<references/> | <references/> | ||
Revision as of 09:32, 4 April 2011
| This Sandbox is Reserved from January 10, 2010, through April 10, 2011 for use in BCMB 307-Proteins course taught by Andrea Gorrell at the University of Northern British Columbia, Prince George, BC, Canada. |
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| 2dds, resolution 1.80Å () | |||||||||
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| Ligands: | |||||||||
| Activity: | Sphingomyelin phosphodiesterase, with EC number 3.1.4.12 | ||||||||
| Related: | 2ddr, 2ddt | ||||||||
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| Resources: | FirstGlance, OCA, PDBsum, RCSB, TOPSAN | ||||||||
| Coordinates: | save as pdb, mmCIF, xml | ||||||||
IntroductionIntroduction
Sphingomyelin phosphodiesterase (Sphingomyelinase): (SMase) is an enzyme which catalyzes the hydrolysis of sphingomyelin (SM) to ceramide and phosphocholine. This enzyme also has hemolytic activity where red blood cells are ruptured and hemoglobin is released into the blood plasma. [1]. This enzyme has become the object of renewed interest since the discovery of the sphingomyelin signal transduction pathway which is involved in apoptosis. This pathway is initiated by a neutral sphingomyelinase hydrolysis of sphingomyelin in the plasma membrane to generate ceramide. Ceramide acts as a secondary messenger which causes the stimulation of the cascade effect of kinases and transcription factors which activate programmed cell death[2]. There are 6 known types of sphingomyelinases[3]. :
Acid sphingomyelinase (aSMase) - aSMase is a soluble lysosomal hydrolase with an optical acivity at pH 5. Acid-SMase has two enzymatic forms: one is targeted to the endo-lysosomal compartment where it coordinates Zn, and the other can be realeased extracellularly through the golgi secretory pathway[4]. A deficiency in results in the lysosomal storage disorder Niemann-Pick disease. Acid-SMase normally metabolizes sphingomyelin which is found in every cell of the body. When aSMase is lacking in the cell, SM builds up and eventually results in cell death[5]. Secretory sphingomyelinase (sSMase) -
Neutral Mg2+-dependent sphingomyelinases (nSMase) - The membrane bound dependent nSMase has an neatral pH optimum and is found predominantly in the brain. This neutral SMase enzyme relies on Magnesium and is activated by unsaturated fatty acids and phosphatidylserine[6].
Neutral Mg2+-independent sphingomyelinases -
Alkaline sphingomyelinase -
Bacterial sphingomyelinase -
Structure and FunctionStructure and Function
Recently, in the 1980's, the primary structure of sphingomyelinase was determined by cloning the first N-SMases from Bacillus cereus and Staphylococcus aureus and by the subsequent sequencing of their cDNAs [7]. The crystal structure of sphingomyelinase has been solved using the bacterium Listeria ivanovii and Bacillus cereus(Bc-SMase) to gain further insight into its catalytic activities [6]. The overall structure of Bc-SMase has been determined to consist of a β-sandwich with α/β motifs[1]. Through SMase structure identification, it has been determined to be a member of the DNA I-like superfamily having geometrically identical amino acid residues as the enzymes in this superfamily. The only different with SMase, is that it has a unique hydrophobic beta-hairpin structure. The crystal structure revealed that this unique beta-hairpin region has two solvent exposed aromatic amino acids on the top which bind to the cell surfaces to catalyze hemolysis.
MechanismMechanism
It has been proposed that the mechanism of Bc-SMase is similar to that of bovine pancreatic DNase 1 because Bc-SMase and bovine DNase 1 are homologous proteins which both have conserved alleged catalytic amino acid residues and a similar molecular structure[7]. . The proposed hydrolytic activity of Bc-SMAse cloned from Bacillus cereus is coordinated by essential water bridged divalent metal ions. Two metal ions which are bound to the Glu-53 and residues in the central cleft which orientate the substrate in the active site. The divalent cation which is linked to His-296 provides a general base water and a phosphate from sphingomelin binds to the central cleft at the site of the water bridged double metal ions. The divalent metal ion which is located at Glu-53 then binds to sphingomelin by directly interacting with the amide oxygen and the O-4 ester oxygen.
ImplicationsImplications
The crystal structure of Bc-SMase has some significant implications for unlocking the poorly characterized structure of neutral sphingomyelinase (nSMase) found in mammals. Bc-SMase is a homologue of nSMase, sharing similar metal ion dependence, amino acid sequence identity, and a similar hydrolytic mechanism[1].
ReferencesReferences
- ↑ 1.0 1.1 1.2 Ago H, Oda M, Takahashi M, Tsuge H, Ochi S, Katunuma N, Miyano M, Sakurai J. Structural basis of the sphingomyelin phosphodiesterase activity in neutral sphingomyelinase from Bacillus cereus. J Biol Chem. 2006 Jun 9;281(23):16157-67. Epub 2006 Apr 4. PMID:16595670 doi:10.1074/jbc.M601089200
- ↑ Kolesnick RN, Haimovitz-Friedman A, Fuks Z. The sphingomyelin signal transduction pathway mediates apoptosis for tumor necrosis factor, Fas, and ionizing radiation. Biochem Cell Biol. 1994 Nov-Dec;72(11-12):471-4. PMID:7544586
- ↑ Goni FM, Alonso A. Sphingomyelinases: enzymology and membrane activity. FEBS Lett. 2002 Oct 30;531(1):38-46. PMID:12401200
- ↑ Jenkins RW, Idkowiak-Baldys J, Simbari F, Canals D, Roddy P, Riner CD, Clarke CJ, Hannun YA. A novel mechanism of lysosomal acid sphingomyelinase maturation: requirement for carboxyl-terminal proteolytic processing. J Biol Chem. 2011 Feb 4;286(5):3777-88. Epub 2010 Nov 22. PMID:21098024 doi:10.1074/jbc.M110.155234
- ↑ Smith EL, Schuchman EH. The unexpected role of acid sphingomyelinase in cell death and the pathophysiology of common diseases. FASEB J. 2008 Oct;22(10):3419-31. Epub 2008 Jun 20. PMID:18567738 doi:10.1096/fj.08-108043
- ↑ 6.0 6.1 Bernardo K, Krut O, Wiegmann K, Kreder D, Micheli M, Schafer R, Sickman A, Schmidt WE, Schroder JM, Meyer HE, Sandhoff K, Kronke M. Purification and characterization of a magnesium-dependent neutral sphingomyelinase from bovine brain. J Biol Chem. 2000 Mar 17;275(11):7641-7. PMID:10713073 Cite error: Invalid
<ref>tag; name "gp6" defined multiple times with different content - ↑ 7.0 7.1 Tomita M, Nakai K, Yamada A, Taguchi R, Ikezawa H. Secondary structure of sphingomyelinase from Bacillus cereus. J Biochem. 1990 Nov;108(5):811-5. PMID:2127932 Cite error: Invalid
<ref>tag; name "gp7" defined multiple times with different content