Fig. 7. (A) A model of one monomer of M. trossulus cMDH, based on the structure of the pig ortholog (PDB accession number 4MDH). All residues that differ between the M. trossulus and the M. galloprovincialis or M. californianus orthologs are labeled; the non-conservative mutation at position 114 is shown in dark spacefill. Representative active site residues are shown in light spacefill, and the highly mobile catalytic loop, which must move by10 Å during catalysis, is black. (B) A magnified view of mutant V114N, showing the relationship of that residue to the catalytic loop (black), as well as the hydrogen bond that may form between the amide nitrogen of the asparagine side chain and the carbonyl oxygen of 143Y on the neighboring helix 1F. Models were visualized with VMD (Humphrey et al., 1996).