Fig. 5. Comparison of wild-type and mutant R-E salt-bridge Kar3 motor domains. Wild-type Kar3 (PDB 1F9T) (Yun et al., 2001) superposed with (A) the E631A (EA) mutant structure (PDB 1F9W) (Yun et al., 2001) or (B) the R598A (RA) mutant structure (PDB 1F9V) (Yun et al., 2001). Blue regions represent areas of least change with <0.5 Å difference between main-chain atoms. Gray areas show differences of 0.5-1.0 Å, after which the color changes to orange (for wild type) or red (for the mutants), becoming solid at 2.0 Å structural difference. Yellow elements are present in the wild-type structure, but not the EA mutant. Green elements are observed in the RA mutant, but not wild-type Kar3. The ADP and Mg²⁺ from wild-type Kar3 are also shown. The arrow in (A) indicates the position of the switch I loop, which becomes disordered in the EA and RA mutants. The arrow in (B) indicates loop 11 and the N-terminus of helix 4, the relay helix, which become ordered upon mutation of R598. The -helix preceding switch I also undergoes a substantial movement in the RA mutant.