Micrococcal nuclease

Ribbon schematic of micrococcal nuclease 3D structure, with Ca²⁺ and TdtP inhibitor

Micrococcal Nuclease (S7 Nuclease or MNase) is an endo-exonuclease that preferentially digests single-stranded nucleic acids.The rate of cleavage is 30 times greater at the 5' side of A or T than at G or C and results in the production of mononucleotides and oligonucleotides with terminal 3'-phosphates. The enzyme is also active against double-stranded DNA and RNA and all sequences will be ultimately cleaved.

Characteristics

The enzyme has a molecular weight of 16.9kDa.

The pH optimum is reported as 9.2. The enzyme activity is strictly dependent on Ca²⁺ and the pH optimum varies according to Ca²⁺ concentration.^[1] The enzyme is therefore easily inacitvated by EGTA.

Source

This enzyme is the extracellular nuclease of Staphylococcus aureus. Two strains, V8 and Foggi, yield almost identical enzymes.^[2] A common source is E.coli cells carrying a cloned nuc gene encoding Staphylococcus aureus extracellular nuclease (micrococcal nuclease).

Structure

The 3-dimensional structure of micrococcal nuclease (then called Staphyloccal nuclease) was solved very early in the history of protein crystallography, in 1969,^[3] deposited as now-obsolete Protein Data Bank file 1SNS. Higher-resolution, more recent crystal structures are available for the apo form as Protein Data Bank file 1SNO: [1] and for the thymidine-diphosphate-inhibited form as Protein Data Bank file 3H6M: [2]. As seen in the ribbon diagram above, the nuclease molecule has 3 long alpha helices and a 5-stranded, barrel-shaped beta sheet, in an arrangement known as the OB-fold (for oligonucleotide-binding fold) as classified in the SCOP database.

Applications

• Hydrolysis of nucleic acids in crude cell-free extracts.
• Sequencing of RNA.
• Preparation of rabbit reticulocytes lysates
• Studies of chromatin structure.
• Remove nucleic acids from protein preparation allowing for folding and structure-function studies.
• Research on the mechanism of protein folding.

References

1. ^ Heins JN, Suriano JR, Taniuchi H, Anfinsen CB (1967). "Characterization of a nuclease produced by Staphylococcus aureus". J. Biol. Chem. 242 (5): 1016–20. PMID 6020427. 
2. ^ Cusumano CL, Taniuchi H, Anfinsen CB (1968). "Staphylococcal nuclease (Foggi strain). I. Order of cyanogen bromide fragments and a "fourth" histidine residue". J. Biol. Chem. 243 (18): 4769–77. PMID 5687719. 
3. ^ Arnone A, Bier J, et al. (1971). "A High Resolution Structure of an Inhibitor Complex of the Extracellular Nuclease of Staphylococcus aureus: I. Experimental Procedures and Chain Tracing". J. Biol. Chem. 246: 2303–2316. 

• http://www.fermentas.com/catalog/modifyingenzymes/nucleasemicrococcal.htm

• http://www.worthington-biochem.com/NFCP/default.html

• http://www.fermentas.com/pdf/msds/en0181_eu.pdf#search=%22micrococcal%20nuclease%22 - A material and safety data sheet for the product

External links

• MeSH Micrococcal+Nuclease
• EC 3.1.31.1