Sandbox Reserved 313: Difference between revisions
No edit summary |
No edit summary |
||
| Line 25: | Line 25: | ||
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>. | 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="gp7">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, Trp-284 and Phe-285, on the top which bind to the cell surfaces to catalyze hemolysis. The hydrolysis and hemolytic activity of Bc-SMase occur in a metal ion dependent manner. Bc-Smase is found in complex with divalent metal ions, Co2+, Mg2+ or Ca2+ in the central cleft of this enzyme. The central cleft acts as an active site, because it contains Glu-53, Asp-195 and His-296 which are involved in Bc-SMase hydrolytic activity. In the central cleft, bound Ca2+ displays a hepta-coordination pattern which is different from the Co2+ and Mg2+ bound forms which are in a double-hexa-coordination forming a double octahedral bi-pyramid. Mg2+ binds to Glu-53 and is required for SM hydrolytic activity and Mg2+ with Ca2+ are required for hemolytic activity. | 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="gp7">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, Trp-284 and Phe-285, on the top which bind to the cell surfaces to catalyze hemolysis. The hydrolysis and hemolytic activity of Bc-SMase occur in a metal ion dependent manner. Bc-Smase is found in complex with divalent metal ions, Co2+, Mg2+ or Ca2+ in the central cleft of this enzyme. The central cleft acts as an active site, because it contains Glu-53, Asp-195 and His-296 which are involved in Bc-SMase hydrolytic activity. In the central cleft, bound Ca2+ displays a hepta-coordination pattern which is different from the Co2+ and Mg2+ bound forms which are in a double-hexa-coordination forming a double octahedral bi-pyramid. Mg2+ binds to Glu-53 and is required for SM hydrolytic activity and Mg2+ with Ca2+ are required for hemolytic activity. | ||
=Mechanism= | =Mechanism= | ||