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A two metal mechanism of group I intron splicing

2005년 3월 14일 15시 59분 44초
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생명화학 - 생명Ⅱ: 화학 생물학
저자 및
Scott Strobel
Yale University, USA,
The group I intron is a self-splicing RNA that is able to remove itself from an RNA transcript while ligating the flanking exons.  Its discovery led to a paradigm shift in biology by showing that not all cellular catalysts are proteins.  We have determined the X-ray crystal structure of an intact intron in complex with both its exons.  The structure includes the nucleophile, the scissile phosphate and the leaving group.  Unlike previous intron structures, this RNA splicing intermediate also includes all the functional groups that have been implicated in catalytic metal ion coordination, including the 2'-OH of the terminal guanosine (wG) within the intron. This RNA construct is catalytically proficient within the crystal.  Thiophillic metal ion rescue experiments identified four catalytic metal ligands in the active site of the intron, including the pro-RP oxygen of the scissile phosphate, the nucleophile (U-1 O3'), the leaving group (wG O3') and the O2' of wG.  These were proposed to be coordinated to three distinct catalytic metal ions.  The structure shows direct metal coordination to all four of these ligands, though these coordinations are satisfied with only two Mg2+ ions.  The distance between the two metals is 3.95Å.  The metal to metal distance and the nature of the metals' coordination to the nucleophile, the scissile phosphate and the leaving group are equivalent to that observed within all known protein based RNA or DNA polymerases.  This suggests that the group I intron splices using a two metal ion mechanism for phosphoryltransfer that is conserved and has been utilized throughout macromolecular evolution.