1a73
From Proteopedia
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INTRON-ENCODED ENDONUCLEASE I-PPOI COMPLEXED WITH DNA
Overview
Homing endonucleases are a diverse collection of proteins that are encoded, by genes with mobile, self-splicing introns. They have also been, identified in self-splicing inteins (protein introns). These enzymes, promote the movement of the DNA sequences that encode them from one, chromosome location to another; they do this by making a site-specific, double-strand break at a target site in an allele that lacks the, corresponding mobile intron. The target sites recognized by these small, endonucleases are generally long (14-44 base pairs). Four families of, homing endonucleases have been identified, including the LAGLIDADG, the, His-Cys box, the GIY-YIG and the H-N-H endonucleases. The first identified, His-Cys box homing endonuclease was I-PpoI from the slime mould Physarum, polycephalum. Its gene resides in one of only a few nuclear introns known, to exhibit genetic mobility. Here we report the structure of the I-PpoI, homing endonuclease bound to homing-site DNA determined to 1.8 A, resolution. I-PpoI displays an elongated fold of dimensions 25 x 35 x 80, A, with mixed alpha/beta topology. Each I-PpoI monomer contains three, antiparallel beta-sheets flanked by two long alpha-helices and a long, carboxy-terminal tail, and is stabilized by two bound zinc ions 15 A, apart. The enzyme possesses a new zinc-bound fold and endonuclease active, site. The structure has been determined in both uncleaved substrate and, cleaved product complexes.
About this Structure
1A73 is a Single protein structure of sequence from Physarum polycephalum with ZN and MG as ligands. Full crystallographic information is available from OCA.
Reference
DNA binding and cleavage by the nuclear intron-encoded homing endonuclease I-PpoI., Flick KE, Jurica MS, Monnat RJ Jr, Stoddard BL, Nature. 1998 Jul 2;394(6688):96-101. PMID:9665136
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