   2.7.7.31 | high-resolution X-ray structures that mimic the pre-catalytic state, the post-catalytic state and a competent state that can be transformed into the two other ones. Zn2+ (or Co2+) in Metal A site changes coordination from octahedral to tetrahedral after the chemical step, which explains the known higher affinity of Tdt for the primer strand when these ions are present, and metal A has to leave to allow the translocation of the primer strand and to clear the active site. Except for Zn2+, the sugar puckering of the primer strand 3' terminus changes from C2'-endo to C3'-endo during catalysis. Metal A is the last component that binds to the active site to complete its productive assembly |
