8-oxoG

Question 1

• How frequently is 8-oxoG formed

Answer 1

o In steady state, there are 2 -3 8-oxoG lesions per 10^6 guanines
o Ogg1 -/- MEF show 2-fold increasein 8-oxoG lesions
o 10 fold increase in response to oxidative stress

o Estimated 100-500 oxidations of G a day
o AP Sites are estimated to occur 2000-10,000 times *spontaneous de-pyrmidiation and de-puration

o Tissue dependent

Question 2

• What is the half life of the 8-oxoG lesion

Answer 2

o Once OGG1 has found the 8-oxoG lesion, the half life is 11 minutes

Question 3

• How is 8-oxoG formed by hydroxy radical

Answer 3

o Hydroxyl radical attacks C8 to form a ketone

Question 4

• Why is guanine the most likely to be oxidized?

Answer 4

o Lower oxidative potential of all the DNA and RNA bases (what is the 2nd??)
o Hypothesized  electron transfer from one base to another over distances of 37 angstroms due to pie stacking interaction between the bases  5’G of a 5’GG’3 doublet is most likely to be oxidized

Question 5

• Consequences of 8-oxoG lesions

Answer 5

o GC to AT transverse mutations
 Can occur during transcription, causing mutant mRNAs
o 8-oxoG dose not impair replication or transcription machinery (but may stall or pause) but oxidized versions of 8-oxoG (hydantoins) and AP sites (intermediates can)
o Interfere with telomere replication

Question 6

• Does the chromatin effect 8-oxoG repair

Answer 6

o At the level of the nucleosome:
 one report showed that 2 uracil glycosylases UNG2 and SMUG1 efficiency was decreased 3- to 9-fold when the uracil containing DNA is wrapped around the nucleosome core particle
 another reported that inhibition of glycosylase was more pronounced when the uracil faced towards the histones
 Another report provided evidence that SWI/SNF (chromatin remodlers) can increase BER activity on 8-oxoG lesion wrapped around a nucleosome
o Chromatin level  BER activity it known to be reduced in these areas, likely due to in accessibility

Question 7

MUTYH function

Answer 7

removes 8-oxoG when adenine in inapproporiaelty paired

Question 8

NEIL 1,2,3

Answer 8

DNA glycosylases and have been shown to efficiently repair spiroimin-odihydantoin (Sp) and guanidinohydantoin (Gh) in addition to other lesions includingthymine glycol, 2,6-diamino-4-hydroxy-5-formamidopyrimidine (FapyG) and 4,6-diamino-5-formamidopyrimidine (FapyA) [