View source for 4lnd


==Crystal structure of human apurinic/apyrimidinic endonuclease 1 with essential Mg2+ cofactor==
<StructureSection load='4lnd' size='340' side='right'caption='[[4lnd]], [[Resolution|resolution]] 1.92&Aring;' scene=''>
== Structural highlights ==
<table><tr><td colspan='2'>[[4lnd]] is a 3 chain structure with sequence from [https://en.wikipedia.org/wiki/Homo_sapiens Homo sapiens]. Full crystallographic information is available from [http://oca.weizmann.ac.il/oca-bin/ocashort?id=4LND OCA]. For a <b>guided tour on the structure components</b> use [https://proteopedia.org/fgij/fg.htm?mol=4LND FirstGlance]. <br>
</td></tr><tr id='method'><td class="sblockLbl"><b>[[Empirical_models|Method:]]</b></td><td class="sblockDat" id="methodDat">X-ray diffraction, [[Resolution|Resolution]] 1.92&#8491;</td></tr>
<tr id='ligand'><td class="sblockLbl"><b>[[Ligand|Ligands:]]</b></td><td class="sblockDat" id="ligandDat"><scene name='pdbligand=MG:MAGNESIUM+ION'>MG</scene></td></tr>
<tr id='resources'><td class="sblockLbl"><b>Resources:</b></td><td class="sblockDat"><span class='plainlinks'>[https://proteopedia.org/fgij/fg.htm?mol=4lnd FirstGlance], [http://oca.weizmann.ac.il/oca-bin/ocaids?id=4lnd OCA], [https://pdbe.org/4lnd PDBe], [https://www.rcsb.org/pdb/explore.do?structureId=4lnd RCSB], [https://www.ebi.ac.uk/pdbsum/4lnd PDBsum], [https://prosat.h-its.org/prosat/prosatexe?pdbcode=4lnd ProSAT]</span></td></tr>
</table>
== Function ==
[https://www.uniprot.org/uniprot/APEX1_HUMAN APEX1_HUMAN] Multifunctional protein that plays a central role in the cellular response to oxidative stress. The two major activities of APEX1 in DNA repair and redox regulation of transcriptional factors. Functions as a apurinic/apyrimidinic (AP) endodeoxyribonuclease in the DNA base excision repair (BER) pathway of DNA lesions induced by oxidative and alkylating agents. Initiates repair of AP sites in DNA by catalyzing hydrolytic incision of the phosphodiester backbone immediately adjacent to the damage, generating a single-strand break with 5'-deoxyribose phosphate and 3'-hydroxyl ends. Does also incise at AP sites in the DNA strand of DNA/RNA hybrids, single-stranded DNA regions of R-loop structures, and single-stranded RNA molecules. Has a 3'-5' exoribonuclease activity on mismatched deoxyribonucleotides at the 3' termini of nicked or gapped DNA molecules during short-patch BER. Possesses a DNA 3' phosphodiesterase activity capable of removing lesions (such as phosphoglycolate) blocking the 3' side of DNA strand breaks. May also play a role in the epigenetic regulation of gene expression by participating in DNA demethylation. Acts as a loading factor for POLB onto non-incised AP sites in DNA and stimulates the 5'-terminal deoxyribose 5'-phosphate (dRp) excision activity of POLB. Plays a role in the protection from granzymes-mediated cellular repair leading to cell death. Also involved in the DNA cleavage step of class switch recombination (CSR). On the other hand, APEX1 also exerts reversible nuclear redox activity to regulate DNA binding affinity and transcriptional activity of transcriptional factors by controlling the redox status of their DNA-binding domain, such as the FOS/JUN AP-1 complex after exposure to IR. Involved in calcium-dependent down-regulation of parathyroid hormone (PTH) expression by binding to negative calcium response elements (nCaREs). Together with HNRNPL or the dimer XRCC5/XRCC6, associates with nCaRE, acting as an activator of transcriptional repression. Stimulates the YBX1-mediated MDR1 promoter activity, when acetylated at Lys-6 and Lys-7, leading to drug resistance. Acts also as an endoribonuclease involved in the control of single-stranded RNA metabolism. Plays a role in regulating MYC mRNA turnover by preferentially cleaving in between UA and CA dinucleotides of the MYC coding region determinant (CRD). In association with NMD1, plays a role in the rRNA quality control process during cell cycle progression. Associates, together with YBX1, on the MDR1 promoter. Together with NPM1, associates with rRNA. Binds DNA and RNA.<ref>PMID:1719477</ref> <ref>PMID:12524539</ref> <ref>PMID:8355688</ref> <ref>PMID:8621488</ref> <ref>PMID:8932375</ref> <ref>PMID:9108029</ref> <ref>PMID:9207062</ref> <ref>PMID:9804799</ref> <ref>PMID:9560228</ref> <ref>PMID:10023679</ref> <ref>PMID:11118054</ref> <ref>PMID:11452037</ref> <ref>PMID:11832948</ref> <ref>PMID:11809897</ref> <ref>PMID:16617147</ref> <ref>PMID:18439621</ref> <ref>PMID:18809583</ref> <ref>PMID:18179823</ref> <ref>PMID:18579163</ref> <ref>PMID:19188445</ref> <ref>PMID:19401441</ref> <ref>PMID:19934257</ref> <ref>PMID:20699270</ref> <ref>PMID:21496894</ref> <ref>PMID:21762700</ref> 
<div style="background-color:#fffaf0;">
== Publication Abstract from PubMed ==
Apurinic/apyrimidinic endonuclease 1 (APE1) mediates the repair of abasic sites and other DNA lesions and is essential for base-excision repair and strand-break repair pathways. APE1 hydrolyzes the phosphodiester bond at abasic sites, producing 5'-deoxyribose phosphate and the 3'-OH primer needed for repair synthesis. It also has additional repair activities, including the removal of 3'-blocking groups. APE1 is a powerful enzyme that absolutely requires Mg(2+), but the stoichiometry and catalytic function of the divalent cation remain unresolved for APE1 and for other enzymes in the DNase I superfamily. Previously reported structures of DNA-free APE1 contained either Sm(3+) or Pb(2+) in the active site. However, these are poor surrogates for Mg(2+) because Sm(3+) is not a cofactor and Pb(2+) inhibits APE1, and their coordination geometry is expected to differ from that of Mg(2+). A crystal structure of human APE1 was solved at 1.92 A resolution with a single Mg(2+) ion in the active site. The structure reveals ideal octahedral coordination of Mg(2+) via two carboxylate groups and four water molecules. One residue that coordinates Mg(2+) directly and two that bind inner-sphere water molecules are strictly conserved in the DNase I superfamily. This structure, together with a recent structure of the enzyme-product complex, inform on the stoichiometry and the role of Mg(2+) in APE1-catalyzed reactions.

Structure of human apurinic/apyrimidinic endonuclease 1 with the essential Mg(2+) cofactor.,Manvilla BA, Pozharski E, Toth EA, Drohat AC Acta Crystallogr D Biol Crystallogr. 2013 Dec;69(Pt 12):2555-62. doi:, 10.1107/S0907444913027042. Epub 2013 Nov 19. PMID:24311596<ref>PMID:24311596</ref>

From MEDLINE&reg;/PubMed&reg;, a database of the U.S. National Library of Medicine.<br>
</div>
<div class="pdbe-citations 4lnd" style="background-color:#fffaf0;"></div>

==See Also==
*[[Apurinic/apyrimidinic endonuclease 3D structures|Apurinic/apyrimidinic endonuclease 3D structures]]
== References ==
<references/>
__TOC__
</StructureSection>
[[Category: Homo sapiens]]
[[Category: Large Structures]]
[[Category: Drohat AC]]
[[Category: Manvilla BA]]
[[Category: Pozharski E]]
[[Category: Toth EA]]