Structure of the exonuclease domain of Lassa NP in complex with 8 bases of dsRNA.

A ribbon model of the immunosuppressive domain of Lassa NP is illustrated in green, with active site D, E, D, D, and H side chains drawn in red. We have arbitrarily modeled the digested strand as the purines and the non-digested strand as the pyrimidines. The substrate (purine) strand is colored purple and its 3′ terminal residue, G8, binds into the active site. The complementary, non-substrate (pyrimidine) strand is colored yellow, and its 5′ terminal residue is C1. One of the two divalent cations required for the exonuclease activity bound in the active site is modeled here as Mg. The second active site divalent cation is not bound due to required mutation of E391 to alanine to prevent digestion of the crystallized dsRNA.