Sandbox Reserved 313: Difference between revisions
No edit summary |
No edit summary |
||
| Line 15: | Line 15: | ||
''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. Magnesium dependent SMase operates in the plasmamembrane <ref name="gp7">PMID: 10713073 </ref>. | ''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. Magnesium dependent SMase operates in the plasmamembrane <ref name="gp7">PMID: 10713073 </ref>. | ||
''Neutral Mg2+-independent sphingomyelinases'' - | ''Neutral Mg2+-independent sphingomyelinases'' - The activities of magnesium independent nSMase are found predominantly in the cytosol and are not very well known<ref name="gp3">PMID: 12401200 </ref>. | ||
''Alkaline sphingomyelinase (bSMase)'' - Alkaline SMase is found in the intestine and hydrolyses sphingomyelin in both the lumen and the mucosal membrane and requires bile salts for activity. This enzyme shares some similarities with the nucleotide pyrophosphatase(NPP) family and is called NPP7. The enzyme has a hydrophobic domain at the N and C terminus, where the N terminus acts as a signal peptide (which is eventually cleaved) and the C terminus acts as a signal anchor which attaches the enzyme to membranes<ref name="gp3">PMID: 12401200 </ref><ref name="gp8">PMID: 16631405 </ref>. | ''Alkaline sphingomyelinase (bSMase)'' - Alkaline SMase is found in the intestine and hydrolyses sphingomyelin in both the lumen and the mucosal membrane and requires bile salts for activity. This enzyme shares some similarities with the nucleotide pyrophosphatase(NPP) family and is called NPP7. The enzyme has a hydrophobic domain at the N and C terminus, where the N terminus acts as a signal peptide (which is eventually cleaved) and the C terminus acts as a signal anchor which attaches the enzyme to membranes<ref name="gp3">PMID: 12401200 </ref><ref name="gp8">PMID: 16631405 </ref>. | ||
| Line 32: | Line 32: | ||
=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="gp">PMID: 16595670 </ref> | It has been proposed by Ago, Hideo. ''et al'' 2006, 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="gp">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 ester oxygen(O4). | 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 ester oxygen(O4). The water briged divalent metal ions, along with Asn-197 chains bind to the oxygens located on thephosphate of sphingomyelin which results in a negative charge on the phosphate group. This results in the phosphorous of SM becoming positively charged. The pKa value of the bound water molecule is lowered through the complex with divalent metal ions and this results in a activated H2O molecule which attacks the phosphorous of SM. Phosphocholine and ceramide are formed through the delocalization of the phosphorous by the divalent metal ionos, through the increased negative charge of the oxygens<ref name="gp">PMID: 16595670 </ref>. | ||