Figure 4.

Solution structure of CbpA R domains. (A) Secondary ¹³C_α chemical shift values for CbpA-R2 showing the three α-helices. Resonances for residues marked by red asterisks are unassigned. (B) Superposed ensemble of 20 lowest-energy structures of CbpA-R2 obtained from solution NMR data; the backbone and select hydrophobic residues (in brown color) at the two α-helix/α-helix interfaces are illustrated. Helix 1 is colored red, Helix 2 blue and Helix 3 green. The location of the YPT motif is noted. (C) End-on view of the three α-helices of domain R2, colored as in (B). (D) Contour maps of electrostatic potentials (±1kt; red, negative potential; blue, positive potential) for CbpA-R2 (left) and homology model of CbpA-R1 (right) generated using GRASP (Nicholls et al, 1991). The α-helices are colored as in (B). Tyr 358 and 363 (magenta; labeled ‘tyrosine fork'), Pro 359 (yellow) and Thr 360 and 362 (orange) are also illustrated. The C_α atoms of other conserved residues are illustrated as colored spheres (Lys 346, Arg 356 and Lys 364 (blue); Glu 352, Asp 354 and Glu 372 (red); Gln 350 and Thr 365 (gray); Ala 347, Ile 368, Ile 370, Ala 371, Val 375, Val 377, Ala 80 and Leu 382 (yellow)). (E) Close-up view of conserved residues in loop between Helix 1 and Helix 2 of CbpA-R2 that protrude into a region of neutral electrostatic potential. Key residues are illustrated as in (D).