FIGURE 1.

IMPDH reaction. A, mechanism of MPA inhibition. R5P, 1-β-d-ribofuranosyl 5-phosphate. B, the alignment of IMPDH-A and IMPDH-B from P. brevicompactum 23078 and Penicillium chrysogenum, IMPDH-A from A. nidulans, and IMPDH2 from Chinese hamster was mapped onto the x-ray crystal structure of the MPA complex of Chinese hamster IMPDH (Protein Data Bank code 1JR1 (8)). Dark magenta, 100% conserved; tan, 58% conserved; dark cyan, 17% conserved. MPA is shown in blue ball and stick, the IMP intermediate in gray ball and stick, K⁺ in purple, and residues within 4 Å of MPA and IMP in stick. Ala-249 is also shown because mutations at this residue confer MPA resistance.