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首页> 外文期刊>Biochemistry >Photocrosslinking Detects a Compact,Active Structure of the Hammerhead Ribozyme
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Photocrosslinking Detects a Compact,Active Structure of the Hammerhead Ribozyme

机译：光交联检测锤头核酶的紧凑，活性结构

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摘要

The hammerhead ribozyme has been intensively studied for approximately 15 years,but its cleavage mechanism is not yet understood.Crystal structures reveal a Y-shaped molecule in which the cleavage site is not ideally aligned for an S_N2 reaction and no RNA functional groups are positioned appropriately to perform the roles of acid and base or other functions in the catalysis.If the ribozyme folds to a more compact structure in the transition state,it probably does so only transiently.We have used photocrosslinking as a tool to trap hammerhead ribozyme-substrate complexes in various stages of folding.Results suggest that the two substrate residues flanking the cleavage site approach and stack upon two guanosines(G8 and G12)in domain 2,moving 10-15 A closer to domain 2 than they appear in the crystal structure.Most crosslinks obtained with the nucleotide analogues positioned in the ribozyme core are catalytically inactive;however,one cobalt(III)hexaammine-dependent crosslink of an unmodified ribozyme retains catalytic activity and confirms the close stacking of cleavage site residue C17 with nucleotide G8 in domain 2.These findings suggest that residues involved in the chemistry of hammerhead catalysis are likely located in that region containing G8 and G12.
机译：锤头状核酶已进行了大约15年的深入研究，但其裂解机理尚不明确。晶体结构显示Y形分子，其裂解位点与S_N2反应的排列不理想，并且没有适当定位RNA官能团核糖核酸在过渡状态下折叠成更紧密的结构，可能只是暂时发生。我们使用光交联作为捕获锤头状核酶-底物复合物的工具结果表明，位于切割位点两侧的两个底物残基接近并堆叠在结构域2中的两个鸟苷（G8和G12）上，比结构中的结构更靠近结构域2 10-15 A.用位于核酶核心的核苷酸类似物获得的交联是催化失活的;但是，一个未修饰的钴（III）六氨依赖的交联fied核酶保留了催化活性并证实了裂解位点残基C17与结构域2中的核苷酸G8紧密堆积。这些发现表明，锤头催化化学过程中涉及的残基可能位于包含G8和G12的区域。

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