Lytic enzymes nucleases

Kinases activate a large group of lytic enzymes by phosphorylation. Lytic enzymes are localized mainly in the cytosol [133]. Their activation requires an acidic pH [134-136]. Thus proteases [137], and nucleases [138,139] are activated which start cell degradation of proteins and nucleic acids. 

In contrast to the lack of detailed structural information for the 3, 5 -cyclic nucleotide phosphodiesterase, staphylococcal (or micrococcal) nuclease (SNase), an extracellular nuclease produced by Staphylococcus aureus, is well characterized. SNase is an extraordinarily efficient catalyst for the endo- and exonucleo-lytic hydrolysis of single-stranded DNA and RNA, with the rate acceleration for DNA being approximately 10 relative to the uncatalyzed rate the final products of the reaction are 3 -mononucleotides. The sequence of 149 amino acids that constitute the enzyme has been determined both by classical degradation procedures and by sequence analysis of the cloned gene. A highly refined 1.65-A X-ray structure determined in the presence of Ca and the competitive inhibitor thymidine 3, 5 -bisphosphate (pdTp) was recently completed (87) this structure differs only slightly from a less refined 1.5-A structure that was reported in 1979... 

Multidimensional NMR spectroscopy provides an alternative method for 3-D structure determination. In fact, this NMR technique is unique in the sense that protein structures can be determined in a solution and noncrystalline state (69, 70). Although still limited in capability, 4-D NMR techniques, in which a 3-D measurement based on N spectra is extended into a fourth dimension by spectra, have been successfully applied to the 153-aa interleukin lj8 (71), providing further insights into the dynamics and folding of the protein molecule. Probing crystalline enzymes by NMR spectroscopy seems to support the claim that crystal structures are representative of the solution structures for most functional purposes. Nevertheless, some differences have been noted when detailed microenvironments are studied. For instance, the pK of His-57 in the catalytic triad of a-lytic protease in crystal is 7.9, nearly one unit higher than that in solution (72). Certain regional sequences may be more flexible and disordered in solution than in the crystal, as has been shown by staphylococcal nuclease (73). 

The nuclease from a marine bacteria Alteromonas espejiana (Bal31) is an extracellular nuclease with wide-ranging substrate specificities. The Alteromonas nuclease is commonly known as Bal31 nuclease, nuclease Bal31, or more simply Bal31. The enzyme catalyzes the degradation of ssDNA both endo- and exonucleo-lytically and of linear dsDNA exonucleolytically from 3 termini generating mostly blunt ends. Products are predominantly 5 -mononucleotides. 

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