Nuclease S1

Nomenclature

Alternative names include endonuclease S1 (Aspergillus), single-stranded-nucleate endonuclease, deoxyribonuclease S1, deoxyribonuclease S1, Aspergillus nuclease S1, Neurospora crassa single-strand specific endonuclease, S1 nuclease, single-strand endodeoxyribonuclease, single-stranded DNA specific endonuclease, single-strand-specific endodeoxyribonuclease, single strand-specific DNase and Aspergillus oryzae S1 nuclease.

Structure

Most nucleases with EC 3.1.30.1 activity are homologous to each other in a protein domain family called Nuclease S1/P1.

Members of this family, including P1 and S1, are glycoproteins with very distinguishing features, they are:

• a requirement for three zinc ions cofactors,
• containing common active site motifs and
• requires an acidic pH for catalysis.
• contains three glycans bound to the amino acid asparagine via N-glycosylation
• two Disulphide bridges between cysteine residues. These requirements and distinguishing features are responsible for function efficacy. It is an enzyme and these four features are needed for enzyme functionality. The three zinc ions are vital for catalysis. The first two zincs activate the attacking water in hydrolysis whilst the third zinc ion stabilizes the leaving oxyanion.

Properties

Aspergillus nuclease S1 is a monomeric protein of a molecular weight of 38 kilodalton. It requires Zn2+ as a cofactor and is relatively stable against denaturing agents like urea, SDS, or formaldehyde. The optimum pH for its activity lies between 4-4.5. Aspergillus nuclease S1 is known to be inhibited somewhat by 50 μM ATP and nearly completely by 1 mM ATP. 50% inhibition has been shown at 85 μM dAMP and 1 μM dATP but uninhibited by cAMP.

Mechanism

This zinc-dependent nuclease protein domain produces 5' nucleotides and cleaves phosphate groups from 3' nucleotides. Additionally, the side chain of tryptophan located in the cavity in the active site and its backbone supports the action one of the zinc ions. Such mechanisms are essential to the catalytic function of the enzyme.

Uses

Aspergillus nuclease S1 is used in the laboratory as a reagent in nuclease protection assays. In molecular biology, it is used in removing single stranded tails from DNA molecules to create blunt ended molecules and opening hairpin loops generated during synthesis of double stranded cDNA.

References

References

1. (February 2012). "An extracellular S1-type nuclease of marine fungus Penicillium melinii". Marine Biotechnology.
2. (February 2011). "Biochemical properties of three plant nucleases with anticancer potential". Plant Science.
3. (September 1998). "Recognition of single-stranded DNA by nuclease P1: high resolution crystal structures of complexes with substrate analogs". Proteins.
4. (July 2011). "DNA-templated ensemble for label-free and real-time fluorescence turn-on detection of enzymatic/oxidative cleavage of single-stranded DNA". Chemical Communications.
5. (November 1979). "Stability of the unique anticodon loop conformation of E.coli tRNAfMet". Nucleic Acids Research.
6. (November 1975). "Specificity of the S1 nuclease from Aspergillus oryzae". The Journal of Biological Chemistry.