Velankar S S, Soultanas P, Dillingham M S, Subramanya H S, Wigley D B
Sir William Dunn School of Pathology, University of Oxford, United Kingdom.
Cell. 1999 Apr 2;97(1):75-84. doi: 10.1016/s0092-8674(00)80716-3.
We have determined two different structures of PcrA DNA helicase complexed with the same single strand tailed DNA duplex, providing snapshots of different steps on the catalytic pathway. One of the structures is of a complex with a nonhydrolyzable analog of ATP and is thus a "substrate" complex. The other structure contains a bound sulphate ion that sits in a position equivalent to that occupied by the phosphate ion produced after ATP hydrolysis, thereby mimicking a "product" complex. In both complexes, the protein is monomeric. Large and distinct conformational changes occur on binding DNA and the nucleotide cofactor. Taken together, these structures provide evidence against an "active rolling" model for helicase action but are instead consistent with an "inchworm" mechanism.
我们确定了与同一种单链带尾DNA双链体复合的PcrA DNA解旋酶的两种不同结构，提供了催化途径中不同步骤的快照。其中一种结构是与ATP的不可水解类似物形成的复合物，因此是一种“底物”复合物。另一种结构包含一个结合的硫酸根离子，其位置与ATP水解后产生的磷酸根离子所占据的位置相当，从而模拟了一种“产物”复合物。在这两种复合物中，蛋白质均为单体。结合DNA和核苷酸辅因子时会发生巨大且明显的构象变化。综上所述，这些结构提供了反对解旋酶作用的“主动滚动”模型的证据，而是与“尺蠖”机制一致。
