The theories for substrate recognition in enzyme catalysis have evolved from lock-key to induced fit, then conformational selection, and conformational selection followed by induced fit. However, the prevalence and consensus of these theories require further examination. Here we use cryogenic electron microscopy and African swine fever virus type 2 topoisomerase (AsfvTop2) to demonstrate substrate binding theories in a joint and ordered manner: catalytic selection by the enzyme, conformational selection by the substrates, then induced fit. The apo-AsfvTop2 pre-exists in six conformers that comply with the two-gate mechanism directing DNA passage and release in the Top2 catalytic cycle. The structures of AsfvTop2-DNA-inhibitor complexes show that substantial induced-fit changes occur locally from the closed apo-conformer that however is too far-fetched for the open apo-conformer. Furthermore, the ATPase domain of AsfvTop2 in the MgAMP-PNP-bound crystal structures coexist in reduced and oxidized forms involving a disulfide bond, which can regulate the AsfvTop2 function.

酶催化中的底物识别理论已经从锁钥匙发展到诱导拟合，然后是构象选择，再到构象选择再诱导拟合。然而，这些理论的普遍性和共识需要进一步检验。在这里，我们使用低温电子显微镜和非洲猪瘟病毒2型拓扑异构酶（Asfv Top2）以联合有序的方式展示底物结合理论：酶的催化选择，底物的构象选择，然后诱导拟合。apo - Asfv Top2 预先存在于六种构象异构体中，这些构象异构体符合在 Top2 催化循环中指导 DNA 通过和释放的双门机制。Asfv Top2-DNA-抑制剂复合物的结构表明，封闭的apo构象在局部发生了显着的诱导拟合变化，但这对于开放的apo构象来说太过牵强。此外，MgAMP-PNP 结合晶体结构中Asfv Top2的 ATPase 结构域以涉及二硫键的还原和氧化形式共存，可以调节Asfv Top2 功能。