Engagement of EBOV NP634 by sdAb ZC. (a) NP634 is shown in sky blue color with interface residues colored yellow, while sdAb interface residues are colored as follows: CDR1, orange; CDR2, green; CDR3, magenta; FR2, red; and FR3, salmon. (b) Top: antibody’s eye view of the epitope on EBOV NP634. Bottom: NP’s eye view of the sdAb paratope. Arrows indicate some of the major complementarities that are visible: yellow, M670 to the sdAb recess; green, CDR2 F52 to the NP basin. (c) Overlay of the sdAb ZC CDRs and FR2, aligned with the NP634’s eye view as cartoons with the bound/unbound color scheme as follows; CDR1, orange/beige; CDR2, green/yellow; CDR3, magenta/pink; FR2, red/salmon. EBOV, Zaire ebolavirus; sdAb, single-domain antibody; ZC, NP, nucleoprotein; FR2, framework 2.