- Blobaum AL, Xu S, Rowlinson SW, Duggan KC, Banerjee S, Kudalkar SN, Birmingham WR, Ghebreselasie K, Marnett LJ. Action at a Distance: Mutations of Peripheral Residues Transform Rapid Reversible Inhibitors to Slow, Tight Binders of Cyclooxygenase-2. The Journal of biological chemistry. 2015 Mar 30. PMID: 25825493 [PubMed].
Cyclooxygenase enzymes (COX-1 and COX-2) catalyze the conversion of arachidonic acid (AA) to prostaglandin (PG)G2. The inhibitory activity of rapid, reversible COX inhibitors (ibuprofen, naproxen, mefenamic acid, and lumiracoxib) demonstrated a significant increase in potency and time-dependence of inhibition against double tryptophan mCOX-2 mutants at the 89/90 and 89/119 positions. In contrast, the slow, time-dependent COX inhibitors (diclofenac, indomethacin, and flurbiprofen) were unaffected by those mutations. Further mutagenesis studies suggested that mutation at position 89 was principally responsible for the changes in inhibitory potency of rapid, reversible inhibitors, while mutation at position 90 may exert some effect on the potency of COX-2-selective diarylheterocycle inhibitors; no effect was observed with mutation at position 119. Several crystal structures with or without NSAIDs indicated that placement of a bulky residue at position 89 caused a closure of a gap at the lobby, and alteration of histidine to tryptophan at position 90 changed the electrostatic profile of the side-pocket of COX-2. Thus, these two residues, especially Val-89 at the lobby region, are crucial for the entrance and exit of some NSAIDs from the COX active site.