Figure 5
Subunit interactions between monomers A and D. (a) The structure of helix α1 and its adjacent loop regions in monomers A and D is shown as a ribbon diagram. The structure of NylCp2-G122 (monomer A, green; monomer D, yellow) is superimposed on the structure of NylCp2 (monomer A, dark green; monomer D, orange). (b) The relationship between the α1 helices in monomers A and D is illustrated. a1, distance between position 112 (monomer A) and position 122 (monomer D) at Cα; a2, distance between position 122 (monomer A) and position 112 (monomer D); b1, distance between position 115 (monomer A) and position 118 (monomer D) at Cα; b2, distance between position 118 (monomer A) and position 115 (monomer D). (c,d). The structure of NylCp2 (c) and the NylCp2-G122 mutant (d) at the A/D monomer interface is shown as a stereo diagram. The side chains of Asp122, Gly122, and Lys159 (monomer A), as well as Glu115 and Tyr156 (monomer D), are shown as stick diagrams in 2Fo-Fc electron density maps. The contour level of the electron density map is 1σ. Possible hydrogen bonds and contacts between two atoms are indicated as dotted lines with the distances listed in Å. (e) The index of symmetry (a2/a1 and b2/b1) is plotted against the protein stability (melting temperature: Tm) estimated from CD analysis of NylCp2 (wild-type) and NylCp2-R122, K122, V122, and G122-mutants. (f) The distance from Lys159-NH3+ (located on helix α2 in monomer A) to Glu115-Oε1− (located on helix α1 in monomer D) is plotted against the Tm.
