Exonuclease snake venom

Using phosphotriester methods, dinucleoside (3 - 50-monophosphates containing 6-methyl-2,-deoxyuridine at the 3 - or 5 -end have been prepared.44 N.m.r. spectroscopy indicates that this nucleoside possesses the syn conformation in these compounds, and, on treatment with snake venom phosphodiesterase, d(m6UpT) is degraded, while d(Apm6U) is not, indicating that this enzyme, a 3 -exonuclease, requires the anti conformation to be present in the substrate. Two modified nucleo-side-5 -monophosphates, (20) and (21), which are resistant to 5 -nucleotidase, have been isolated from tRNA snake venom hydrolysates.45 A synthesis of (20) has been reported.46... 

When the Tg lesions is opened by ammonolysis, the resulting product (ureidoisobutyric acid) inhibits snake venom phosphodiesterase, A exonuclease and the Klenow (exo ) fragment (Matray et al. 1995 see also Greenberg and Matray 1997). It is, however, removed by E. coli Fpg and Nth proteins (Jurado et al. 1998). 

Determination of the stereochemical course of the reactions catalyzed by the exonucleases from snake venom and bovine spleen and by Staphylococcal nuclease is in progress. 

Snake Venom Phosphodiesterase An exonuclease is an enzyme that sequentially cleaves nucleotides from the end of a polynucleotide strand. Snake venom phosphodiesterase, which hydrolyzes nucleotides from the 3 end of any oligonucleotide with a free 3 -hydroxyl group, cleaves between the 3 hydroxyl of the ribose or deoxyribose and the phosphoryl group of the next nucleotide. It acts on single-stranded DNA or RNA and has no base specificity. This enzyme was used in sequence... 

The mutagenic ribonucleotide rPTP (87) has been used in an in vitro retroviral replication model. After four rounds of replication the mutation frequency was raised to 3.8 x 10 per nucleotide, with C U and U C mutations observed. It was suggested that such an analogue could induce mutations in a retroviral target beyond its error threshold. The tricyclic cytosine analogues phenoxazine and 9-(2-aminoethoxy)-phenoxazine (g-clamp, see (141)) have been incorporated into ODNs to study their effect with exonuclease. It was found that a single substitution at the 3 -terminus afforded complete protection of the ODN with snake venom phosphodiesterase. ... 

Snake venom phosphodiesterase and polynucleotide phos-phorylase. Snake venom diesterase is an exonuclease that hydrolyzes both DNA and RNA it can be isolated from the venom of many poisonous snakes. It attacks sequentially from the 3 -OH end and yields 5 -phosphates. Polynucleotide phosphorylase (PNPase) has a similar mode of action. As the name indicates, it is a phosphorylase and not a... 

Spleen (and micrococcal) phosphodiesterase. These exonucleases act on DNA and RNA in a direction that is the reverse of snake venom phosphodiesterase, i.e., they start from the 5 -OH and yield sequentially 3 -phosphates. They... 

The boranophosphate internucleotide linkage in dimer 2 is quite stable toward cleavage by exonucleases. Enzymatic hydrolysis studies were performed on TpT in vitro (normal dinucleotide), and a mixture of R and S boronated diastereomers of TpBT 2 to ascertain the in vitro exonuclease resistance of the intemucleotide linkage (12). Under conditions where normal dithymidylyl phosphate is >97% cleaved, dimer 2 is >92% stable to both calf spleen and snake venom phosphodiesterase. The boronation confers considerable resistance to these two particular exonucleases. The extent of protection shows that both the R and S chiral forms exhibit nuclease resistance. These experiments are now being repeated for the R and S stereoisomers of the dimer, which we have separated by HPLC. In summary, the P—BH3 group possesses sufficient hydrolytic stability to survive use in biological systems. 

B. Phosphodiesterase. Snake venoms commonly contain enzymes that hydrolyze phosphodiester bonds. There are two types of phosphodiesterase one is an exonuclease and the second is an endonuclease. 

Snake venom exonucleases can hydrolyze almost any type of polynucleotide of any chain length. The type of bases, linkages, and sugars do not have much effect on the rate of hydrolysis. Thus, the enzyme hydrolyzes RNA, DNA, synthetic polynucleotides, and native or denatured DNA. 

Frequently, the presence of ATPase in snake venoms is described. However, it is clear that the hydrolysis of ATP is due to the action of an exonuclease rather than the separate enzyme, ATPase. 

The ATPase of most biological systems hydrolyzes the a-phosphate producing ADP + Pj. When ATP is used as a substrate, snake venom exonuclease hydrolyzes it to AMP and PP (pyrophosphate). However, when ATP is mixed with snake venom, it is hydrolyzed to adenosine, Pj and PP because snake venom contains an additional enzyme, 5 -nucleotidase. This can be summarized as follows ... 

The enzyme NADase should not be confused with nucleotide pyrophosphatase. The products of nucleotide pyrophosphatase are nicotinamide mononucleotide and 5 -AMP. In snake venoms, there is no separate nucleotide pyrosphosphatase, but the action is due to snake venom exonuclease (phosphodiesterase). 

Venom has long been known to be a good source of several enzymes that hydrolyze esters of phosphoric acid. It is not possible to discuss venom exonuclease without mentioning other enzymes of this group. An effort will be made, however, to limit the discussion of other phosphatases to the bare essentials and key references. The surveys of different species of snake with respect to these enzymes are fairly numerous (1-9) and allow several conclusions to be drawn. 

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