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. 2020 Sep 29;12(10):1109. doi: 10.3390/v12101109

Figure 4.

Figure 4

Schematic representation of the task specialization of each ZK upon binding to NA. The NA fragment is in red, NC ZKs are in cyan (ZK1) and green (ZK2), NC Nter and Cter tails are in grey and purple, respectively, and the inter-ZK linker is in orange. In the NA-free form of NC, interactions between the more rigid part of the linker and ZK1 are represented with dashed lines in green. In addition, within the linker, the Gly35 dynamic hinge is shown (see paragraph 3.2 and Figure 3). This dynamic hinge is not retained in NA-bound forms of NC, Gly35 being directly involved in the guanine recognition within ZK2 (see Figure 2C). (A) Situation 1, with two accessible guanines. The ZK1-linker interactions render ZK1 less accessible than ZK2. Thus, ZK2 binds first to an accessible guanine, and ZK1 binds the remaining guanine. The stem is not destabilized. (B) Situation 2, with only one accessible guanine. Similarly, ZK2 binds first to the unique accessible guanine, and ZK1 remains free to contact the stem via its large hydrophobic platform. The stem is destabilized (in dark blue).