Structural constraints on protein self-processing in L-aspartate-α-decarboxylase
Structural constraints on protein self-processing in L-aspartate-α-decarboxylase
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DOI：
10.1093/emboj/cdg575
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发表时间：
2003-12-01
期刊：
影响因子：
11.4
通讯作者：
Blundell, TL
中科院分区：
文献类型：
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作者：
Schmitzberger, F;Kilkenny, ML;Blundell, TL
天冬氨酸脱羧酶被翻译为前蛋白，在Gly 24-Ser 25处进行分子内自切割。我们已经确定了一个未加工的天然前体的晶体结构，除了Ala 24插入，Ala 26插入和Gly 24->Ser，His 11->Ala，Ser 25->Ala，Ser 25->Cys和Ser 25->Thr突变体。裂解位点的比较分析揭示了特定的构象约束，支配自我加工，并表明，相当大的重排必须发生。我们认为，Thr 57 Ogamma和水分子形成一个“含氧阴离子孔”，可能稳定拟议的氧恶唑烷中间体。Thr 57和该水分子可能是能够支持酸碱催化的催化残基。裂解位点之前的环中的构象自由度似乎在反应中起决定性作用。这里提出的自加工的分子机制强调了氧恶唑烷中间体稳定化的重要性。结构特征的比较表明，显着的相似性，在其他的自我加工系统，并建议，模型的切割位点的这种酶的基础上的Ser-->Ala或Ser-->Thr突变体单独可能会导致错误的解释机制。
Aspartate decarboxylase, which is translated as a pro-protein, undergoes intramolecular self-cleavage at Gly24-Ser25. We have determined the crystal structures of an unprocessed native precursor, in addition to Ala24 insertion, Ala26 insertion and Gly24-->Ser, His11-->Ala, Ser25-->Ala, Ser25-->Cys and Ser25-->Thr mutants. Comparative analyses of the cleavage site reveal specific conformational constraints that govern self-processing and demonstrate that considerable rearrangement must occur. We suggest that Thr57 Ogamma and a water molecule form an 'oxyanion hole' that likely stabilizes the proposed oxyoxazolidine intermediate. Thr57 and this water molecule are probable catalytic residues able to support acid-base catalysis. The conformational freedom in the loop preceding the cleavage site appears to play a determining role in the reaction. The molecular mechanism of self-processing, presented here, emphasizes the importance of stabilization of the oxyoxazolidine intermediate. Comparison of the structural features shows significant similarity to those in other self-processing systems, and suggests that models of the cleavage site of such enzymes based on Ser-->Ala or Ser-->Thr mutants alone may lead to erroneous interpretations of the mechanism.