Fig. 3.

The x-ray crystal structure of the MBP–monobody MBP-74 fusion protein. (A) A helical rod of the fusion proteins formed in the crystal along crystallographic 4₁-screw axis. Four symmetry-related copies of the fusion protein are shown in different colors, and the MBP and monobody portions are shown in lighter and darker shades, respectively. A schematic representation of the packing is also shown. (B) The binding complex of MBP (white) and monobody (blue) with the MBP fusion partner (cyan). A close-up image of the linker region with electron density is also shown. (C) The binding complex rotated ≈90° along the vertical axis with respect to that shown in B. (D) The epitope shown on the MBP surface. Red, orange, and yellow surfaces indicate those for atoms within 3.2, 4.0, and 5.0 Å of monobody atoms, respectively. (E) Epitope mapped by NMR spectroscopy. Red, yellow, and white spheres indicate the Cα atom positions for residues whose NMR signals are strongly affected, weakly affected, and not affected, respectively. (F) A comparison of the backbone conformation of the recognition loops between monobody MBP-74 and wild-type FNfn10 (PDB ID code 1FNF). The BC, DE, and FG loops of the monobody are shown in cyan, yellow, and green, respectively, and those of wild-type FNfn10 are shown in tan. Residue numbers are also shown.