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Search The CSA
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Catalytic Site Atlas

CSA LITERATURE entry for 1c54

E.C. nameribonuclease T1
SpeciesStreptomyces aureofaciens (Bacteria)
E.C. Number (IntEnz) 3.1.27.3
CSA Homologues of 1c54There are 78 Homologs
CSA Entries With UniProtID P05798
CSA Entries With EC Number 3.1.27.3
PDBe Entry 1c54
PDBSum Entry 1c54
MACiE Entry 1c54

Literature Report

IntroductionRibonuclease Sa is a small microbial guanosine-specific endoribonuclease. It is homologous to two microbial ribonucleases, ribonuclease T1 and ribonuclease Ba.
MechansimThe cleavage of substrate by ribonucleases is a two-step reaction: the first step is a transesterification of which a nucleophilic displacement at the phosphorus atom of the 5' leaving group by the 2' entering oxygen atom takes place, forming a guanosine 2',3'-cyclophosphate intermediate, which is hydrolysed in the second step to yield 3' guanylic acid.
In the case of ribonuclease Sa, Glu54 acts as a base to deprotonate the ribose 2'OH group to promote its nucleophilic attack on the phosphorus atom of the 5'leaving group. His85 acts as an acid to donate a proton to the leaving group. Arg65 promotes the formation of a negatively charged, pentacovalent phosphate group in the transition state.
Reaction

Catalytic Sites for 1c54

Annotated By Reference To The Literature - Site 1 (Perform Site Search)
ResidueChainNumberUniProtKB NumberFunctional PartFunctionTargetDescription
HisA8585macie:sideChainIt acts as an acid to donate a proton to the leaving group.
GluA5454macie:sideChainIt acts as a base to deprotonate the ribose 2'OH group to promote its nucleophilic attack on the phosphorus atom of the 5'leaving group.
ArgA6565macie:sideChainIt stabilises the negatively charged, pentacovalent phosphate transition state.

Literature References

Notes:
Yakovlev GI
Contribution of active site residues to the activity and thermal stability of ribonuclease Sa.
Protein Sci 2003 12 2367-2373
PubMed: 14500895
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