Abstract
Osteoporosis and low bone mass are currently estimated to be a major public health risk affecting > 50% of the female population over the age of 50. Because of their bone-selective pharmacokinetics, nitrogen-containing bisphosphonates (N-BPs), currently used as clinical inhibitors of bone-resorption diseases, target osteoclast farnesyl pyrophosphate synthase (FIRPS) and inhibit protein prenylation. FIRPS, a key branchpoint of the mevalonate pathway, catalyzes the successive condensation of isopentenyl pyrophosphate with dimethylallyl pyrophosphate and geranyl pyrophosphate. To understand the molecular events involved in inhibition of FPPS by N-BPs, we used protein crystallography, enzyme kinetics, and isothermal titration calorimetry. We report here high-resolution x-ray structures of the human enzyme in complexes with risedronate and zoledronate, two of the leading N-BPs in clinical use. These agents bind to the dimethylallyl/ geranyl pyrophosphate ligand pocket and induce a conformational change. The interactions of the N-BP cyclic nitrogen with Thr-201 and Lys-200 suggest that these inhibitors achieve potency by positioning their nitrogen in the proposed carbocation-binding site. Kinetic analyses reveal that inhibition is competitive with geranyl pyrophosphate and is of a slow, tight binding character, indicating that isomerization of an initial enzyme-inhibitor complex occurs with inhibitor binding. Isothermal titration calorimetry indicates that binding of N-BPs to the apoenzyme is entropy-driven, presumably through desolvation entropy effects. These experiments reveal the molecular binding characteristics of an important pharmacological target and provide a route for further optimization of these important drugs.
Original language | English |
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Pages (from-to) | 7829-7834 |
Number of pages | 5 |
Journal | PNAS |
Volume | 103 |
Issue number | 20 |
DOIs | |
Publication status | Published - May 2006 |
Keywords
- farnesyl pyrophosphate synthase
- osteoclast
- slow, tight inhibition
- farnesyl diphosphate synthase
- trans-prenyltransferase
- bone-resorption
- in-vivo
- mevalonate pathway
- liver prenyltransferase
- isoprenoid biosynthesis
- pyrophosphate synthase
- binding energetics
- structural basis
- inhibition