1hd7: Difference between revisions

The major human abasic endonuclease, Ape1, is an essential DNA repair, enzyme that initiates the removal of apurinic/apyrimidinic sites from DNA, excises 3' replication-blocking moieties, and modulates the DNA binding, activity of several transcriptional regulators. We have determined the, X-ray structure of the full-length human Ape1 enzyme in two new crystal, forms, one at neutral and one at acidic pH. The new structures are, generally similar to the previously determined structure of a truncated, Ape1 protein, but differ in the conformation of several loop regions and, in spans of residues with weak electron density. While only one, active-site metal ion is present in the structure determined at low pH, the structure determined from a crystal grown at the pH optimum of Ape1, nuclease activity, pH 7.5, has two metal ions bound 5 A apart in the, active site. Enzyme kinetic data indicate that at least two metal-binding, sites are functionally important, since Ca(2+) exhibits complex, stimulatory and inhibitory effects on the Mg(2+)-dependent catalysis of, Ape1, even though Ca(2+) itself does not serve as a cofactor. In, conjunction, the structural and kinetic data suggest that Ape1 catalyzes, hydrolysis of the DNA backbone through a two metal ion-mediated mechanism.

1HD7 is a [http://en.wikipedia.org/wiki/Single_protein Single protein] structure of sequence from [http://en.wikipedia.org/wiki/Homo_sapiens Homo sapiens] with PB as [http://en.wikipedia.org/wiki/ligand ligand]. Active as [http://en.wikipedia.org/wiki/DNA-(apurinic_or_apyrimidinic_site)_lyase DNA-(apurinic or apyrimidinic site) lyase], with EC number [http://www.brenda-enzymes.info/php/result_flat.php4?ecno=4.2.99.18 4.2.99.18] Structure known Active Site: PB1. Full crystallographic information is available from [http://ispc.weizmann.ac.il/oca-bin/ocashort?id=1HD7 OCA].  

''Page seeded by [http://ispc.weizmann.ac.il/oca OCA ] on Mon Nov  5 15:10:26 2007''