Fig 3.

Comparison of the 270-loop in different NAs. (A) Superimposed 270-loops of VN04N1 (orange), N2 (blue), and N3 (yellow). The 270-loop of N1 is much closer to the 240-loop. (B) Y273 in VN04N1 forms hydrogen bonds with Y252, Q249, and A270, which produces a tight turn in the 270-loop. (C) Q273 and A272 in N2 hydrogen bond to Y316 and S314, respectively, thus pulling the 270-loop in N2 to turn in the opposite direction of the N1 loop. (D) Q273 in N3 hydrogen bonds with Y252, K270, Y316, and I272 and K271′ hydrogen bonds with T314.