Abstract
Farnesyl pyrophosphate synthetase (FPPS) synthesizes farnesyl pyrophosphate through successive condensations of isopentyl pyrophosphate with dimethylallyl pyrophosphate and geranyl pyrophosphate. Nitrogen-containing bisphosphonate drugs used to treat osteoclast-mediated bone resorption and tumor-induced hypercalcemia are potent inhibitors of the enzyme. Here we present crystal structures of substrate and bisphosphonate complexes of FPPS. The structures reveal how enzyme conformational changes organize conserved active site residues to exploit metal-induced ionization and substrate positioning for catalysis. The structures further demonstrate how nitrogen-containing bisphosphonates mimic a carbocation intermediate to inhibit the enzyme. Together, these FPPS complexes provide a structural template for the design of novel inhibitors that may prove useful for the treatment of osteoporosis and other clinical indications including cancer.
Highlights
Farnesyl pyrophosphate synthetase (FPPS) synthesizes farnesyl pyrophosphate through successive condensations of isopentyl pyrophosphate with dimethylallyl pyrophosphate and geranyl pyrophosphate
S. aureus FPPS—The structure of FPPS-Sa confirms the conservation of the 3-layered all ␣-helical prenyltransferase fold and reveals regions of conformational flexibility important for enzyme activity (Fig. 2A)
The 2.4-Å structure of the IPP1⁄7DMSPP ternary complex reveals the structural basis for this three-step mechanism
Summary
Farnesyl pyrophosphate synthetase (FPPS) synthesizes farnesyl pyrophosphate through successive condensations of isopentyl pyrophosphate with dimethylallyl pyrophosphate and geranyl pyrophosphate. The structures further demonstrate how nitrogen-containing bisphosphonates mimic a carbocation intermediate to inhibit the enzyme Together, these FPPS complexes provide a structural template for the design of novel inhibitors that may prove useful for the treatment of osteoporosis and other clinical indications including cancer. Post-translational modification of C-terminal CAAX sequences by covalent attachment of isoprenyl chains is crucial for intracellular localization and proper function of small GTPases such as Ras, Rac, Rho, and CDC42 [1, 2] The substrates for these modifications are the 15-carbon isoprenoid farnesyl pyrophosphate (FPP) or the 20-carbon isoprenoid geranyl-geranyl pyrophosphate synthesized by enzymes of the mevalonate pathway [3] (Fig. 1A). Because of their bone-targeting properties, bisphosphonates have found use as agents to treat tumor-induced hypercalcemia [13], Paget’s disease [14], and osteolytic metastases [15]
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