Structure of the ForT/PRPP complex uncovers the mechanism of C-C bond formation in C-nucleotide antibiotic biosynthesis

C-C bond formation is at the heart of anabolism and organic chemistry, but relatively few enzymatic strategies for catalyzing this reaction are known. The enzyme ForT catalyzes C-C bond formation between 5-phosphoribosyl-1-pyrophosphate (PRPP) and 4-amino-1H-pyrazole-3,5-dicarboxylate to make a key intermediate in the biosynthesis of the C-nucleotide formycin A 5-phosphate; we now report the 2.5 [A] resolution structure of the ForT/PRPP complex and thus locate the active site. Site-directed mutagenesis has identified those residues critical for PRPP recognition and catalysis. Structural conservation with GHMP kinases suggests that stabilization of the negatively charged pyrophosphate leaving group is crucial for catalysis in ForT. A mechanism for this new class of C-C bond forming enzymes is proposed. Entry for the Table of Contents O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=180 SRC="FIGDIR/small/009662v1_ufig1.gif" ALT="Figure 1"> View larger version (12K): org.highwire.dtl.DTLVardef@1817d54org.highwire.dtl.DTLVardef@4b3558org.highwire.dtl.DTLVardef@19b248eorg.highwire.dtl.DTLVardef@7d0c62_HPS_FORMAT_FIGEXP M_FIG C_FIG A new class of enzymes catalyse C-C bond formation by irreversible CO2 and pyrophosphate production.