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Bifunctional 8-oxoguanine-DNA glycosylase (OGG1), a crucial DNA-repair enzyme, removes from DNA 8-oxo-7,8-dihydroguanine (8-oxoG) with following cleavage of the arising apurinic/apyrimidinic (AP) site. The major enzyme in eukaryotic cells that catalyzes the cleavage of AP sites is AP endonuclease 1 (APE1). Alternatively, AP sites can be cleaved by tyrosyl-DNA phosphodiesterase 1 (TDP1) to initiate APE1-independent repair, thus expanding the ability of the base excision repair (BER) process. Poly(ADP-ribose) polymerase 1 (PARP1) is a regulatory protein of DNA repair. PARP2 is also activated in response to DNA damage and can be regarded as the BER participant. Here we analyze PARP1 and PARP2 interactions with DNA intermediates of the initial stages of the BER process (8-oxoG and AP-site containing DNA) and their interplay with the proteins recognizing and processing these DNA structures focusing on OGG1. OGG1 as well as PARP1 and PARP2 form covalent complex with AP site-containing DNA without borohydride reduction. AP site incision by APE1 or TDP1 removal of protein adducts but not proteins’ PARylation prevent DNA-protein crosslinks.

Abstract: Brain tissues from Alzheimer's disease (AD) patients show increased levels of oxidative DNA damage and 7,8-dihydro-8-oxoguanine (8-oxoG) accumulation. In humans, the base excision repair protein 8-oxoguanine-DNA glycosylase (OGG1) is the major enzyme that recognizes and excises the mutagenic DNA base lesion 8-oxoG. Recently, two polymorphisms of OGG1, A53T and A288V, have been identified in brain tissues of AD patients, but little is known about how these polymorphisms may contribute to AD. We characterized the A53T and A288V polymorphic variants and detected a significant reduction in the catalytic activity for both proteins in vitro and in cells. Additionally, the A53T polymorphism has decreased substrate binding, whereas the A288V polymorphism has reduced AP lyase activity. Both variants have decreased binding to known OGG1 binding partners PARP-1 and XRCC1. We found that OGG1−/− cells expressing A53T and A288V OGG1 were significantly more sensitive to DNA damage and had significantly decreased survival. Our results provide both biochemical and cellular evidence that A53T and A288V polymorphic proteins have deficiencies in catalytic and protein-binding activities that could be related to the increase in oxidative damage to DNA found in AD brains. [Copyright &y& Elsevier]

Specific and nonspecific DNA complex formation with human uracil-DNA glycosylase, 8-oxoguanine-DNA glycosylase, and apurine/apyrimidine endonuclease, as well as with E. coli 8-oxoguanine-DNA glycosylase and RecA protein was analyzed using the method of stepwise increase in DNA-ligand complexity. It is shown that high affinity of these enzymes to any DNA (10-10 M) is provided by a large number of weak additive contacts mainly with DNA internucleoside phosphate groups and in a less degree with bases of nucleotide links 'covered' by protein globules. Enzyme interactions with specific DNA links are comparable in efficiency with weak unspecific contacts and provide only for one-two orders of affinity (10-10 M), but these contacts are extremely important at stages of DNA and enzyme structural adaptation and catalysis proper. Only in the case of specific DNA individual for each enzyme alterations in DNA structure provide for efficient adjustment of reacting enzyme atoms and DNA orbitals with accuracy up to 10-15° and, as a result, for high reaction rate. Upon transition from nonspecific to specific DNA, reaction rate ( k) increases by 4-8 orders of magnitude. Thus, stages of DNA and enzyme structural adaptation as well as catalysis proper are the basis of specificity of repair enzymes. [ABSTRACT FROM AUTHOR]

Abstract: Human 8-oxoguanine–DNA glycosylase OGG1 is an enzyme that removes abundant oxidative lesion 8-oxoguanine (8-oxoG) from DNA. Excision of 8-oxoG by OGG1 is inhibited by the abasic DNA reaction product and is stimulated by AP endonuclease APEX1. Besides 8-oxoG, OGG1 shows activity towards several other base lesions. Here we report that APEX1 efficiently stimulates OGG1 on good substrates (8-oxoadenine, 8-oxoinosine, or 6-methoxy-8-oxoguanine opposite to cytosine) but the stimulation is low or absent with poor OGG1 substrates (8-oxoadenine or 8-oxoinosine opposite to thymine; 8-oxoG or 8-aminoguanine opposite to adenine; 8-oxonebularine, 8-metoxyguanine, inosine or guanine opposite to cytosine). APEX1 significantly improves the ability of OGG1 to excise 8-aminoguanine from its naturally occurring pair with cytosine, making it possible that OGG1 repairs this lesion. Overall, APEX1 serves to improve specificity of OGG1 for its biologically relevant substrates. [Copyright &y& Elsevier]

Abstract: Human 8-oxoguanine-DNA glycosylase (OGG1) is the main human base excision protein that removes a mutagenic lesion 8-oxoguanine (8-oxoG) from DNA. Since OGG1 has DNA glycosylase and weak abasic site (AP) lyase activities and is characterized by slow product release, turnover of the enzyme acting alone is low. Recently it was shown that human AP endonuclease (APE1) enhances the activity of OGG1. This enhancement was proposed to be passive, resulting from APE1 binding to or cleavage of AP sites after OGG1 dissociation. Here we present evidence that APE1 could actively displace OGG1 from its product, directly increasing the turnover of OGG1. We have observed that APE1 forms an electrophoretically detectable complex with OGG1 cross-linked to DNA by sodium borohydride. Using oligonucleotide substrates with a single 8-oxoG residue located in their 5′-terminal, central or 3′-terminal part, we have demonstrated that OGG1 activity does not increase only for the first of these three substrates, indicating that APE1 interacts with the DNA stretch 5′ to the bound OGG1 molecule. In kinetic experiments, APE1 enhanced the product release constant but not the rate constant of base excision by OGG1. Moreover, OGG1 bound to a tetrahydrofuran analog of an abasic site stimulated the activity of APE1 on this substrate. Using a concatemeric DNA substrate, we have shown that APE1 likely displaces OGG1 in a processive mode, with OGG1 remaining on DNA but sliding away in search for a new lesion. Altogether, our data support a model in which APE1 specifically recognizes an OGG1/DNA complex, distorts a stretch of DNA 5′ to the OGG1 molecule, and actively displaces the glycosylase from the lesion. [Copyright &y& Elsevier]

Bifunctional 8-oxoguanine-DNA glycosylase (OGG1), a crucial DNA-repair enzyme, removes from DNA 8-oxo-7,8-dihydroguanine (8-oxoG) with following cleavage of the arising apurinic/apyrimidinic (AP) site. The major enzyme in eukaryotic cells that catalyzes the cleavage of AP sites is AP endonuclease 1 (APE1). Alternatively, AP sites can be cleaved by tyrosyl-DNA phosphodiesterase 1 (TDP1) to initiate APE1-independent repair, thus expanding the ability of the base excision repair (BER) process. Poly(ADP-ribose) polymerase 1 (PARP1) is a regulatory protein of DNA repair. PARP2 is also activated in response to DNA damage and can be regarded as the BER participant. Here we analyze PARP1 and PARP2 interactions with DNA intermediates of the initial stages of the BER process (8-oxoG and AP-site containing DNA) and their interplay with the proteins recognizing and processing these DNA structures focusing on OGG1. OGG1 as well as PARP1 and PARP2 form covalent complex with AP site-containing DNA without borohydride reduction. AP site incision by APE1 or TDP1 removal of protein adducts but not proteins' PARylation prevent DNA-protein crosslinks., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. The handling editor declared a shared affiliation and a past co-authorship with one of the authors OL at the time of review., (Copyright © 2021 Lebedeva, Rechkunova, Endutkin and Lavrik.)